chapter 12 mammalian biochronology of blancan and irvingtonian

269

Chapter 12

Mammalian Biochronology of Blancan and Irvingtonian(Pliocene and Early Pleistocene) Faunas from New Mexico

GARY S. MORGAN1 AND SPENCER G. LUCAS2

ABSTRACT

Significant mammalian faunas of Pliocene (Blancan) and early Pleistocene (early and medialIrvingtonian) age are known from the Rio Grande and Gila River valleys of New Mexico.Fossiliferous exposures of the Santa Fe Group in the Rio Grande Valley, extending from theEspanola basin in northern New Mexico to the Mesilla basin in southernmost New Mexico,have produced 21 Blancan and 6 Irvingtonian vertebrate assemblages; three Blancan faunasoccur in the Gila River Valley in the Mangas and Duncan basins in southwestern New Mexico.More than half of these faunas contain five or more species of mammals, and many haveassociated radioisotopic dates and/or magnetostratigraphy, allowing for correlation with theNorth American land-mammal biochronology. Two diverse early Blancan (4.5–3.6 Ma) faunasare known from New Mexico, the Truth or Consequences Local Fauna (LF) from the Palomasbasin and the Buckhorn LF from the Mangas basin. The former contains five species ofmammals indicative of the early Blancan: Borophagus cf. B. hilli, Notolagus lepusculus, Neo-toma quadriplicata, Jacobsomys sp., and Odocoileus brachyodontus. Associated magnetostra-tigraphic data suggest correlation with either the Nunivak or Cochiti Subchrons of the GilbertChron (4.6–4.2 Ma), which is in accord with the early Blancan age indicated by the mam-malian biochronology. The Truth or Consequences LF is similar in age to the Verde LF fromArizona, and slightly older than the Rexroad 3 and Fox Canyon faunas from Kansas. TheBuckhorn LF has 18 species of mammals, including two rodents typical of the early Blancan,Mimomys poaphagus and Repomys panacaensis. The Buckhorn LF also is similar in age tothe Verde LF and has affinities with the Panaca LF from Nevada. Although the Buckhorn andTruth or Consequences LFs have few taxa in common, the similarities of both faunas with theVerde LF suggest they are close in age.

Eight faunas from the central and southern Rio Grande Valley are medial Blancan in age(3.6–2.7 Ma), including the Pajarito and Belen faunas from the Albuquerque basin, the Arroyode la Parida LF from the Socorro basin, the Cuchillo Negro Creek and Elephant Butte LakeLFs from the Engle basin, the Palomas Creek LF from the Palomas basin, the Hatch LF fromthe Hatch-Rincon basin, and the Tonuco Mountain LF from the Jornada basin. These faunasare characterized by the presence of taxa absent from early Blancan faunas, including Geomys(Nerterogeomys) paenebursarius, Equus cumminsii, E. scotti, and Camelops, and the absenceof South American immigrant mammals found in late Blancan faunas. The Pajarito LF isdirectly associated with a pumice dated at 3.1 Ma. The Cuchillo Negro Creek and ElephantButte Lake LFs are in close stratigraphic association with a basalt flow of 2.9 Ma. Magneto-stratigraphy constrains the age of the Tonuco Mountain LF between 3.6 and 3.0 Ma.

The Mesilla A fauna from the Mesilla basin and the Pearson Mesa LF from the Duncanbasin are late Blancan in age (2.7–2.2 Ma). Both record the association of Nannippus with aSouth American immigrant, Glyptotherium from Mesilla A and Glossotherium from PearsonMesa, restricting their age to the interval after the beginning of the Great American Interchangeat about 2.7 Ma and before the extinction of Nannippus ca. 2.2 Ma. Magnetostratigraphy

1 Curator of Vertebrate Paleontology, New Mexico Museum of Natural History, 1801 Mountain Road NW, Albu-querque, NM 87104.

2 New Mexico Museum of Natural History, 1801 Mountain Road NW, Albuquerque, NM 87104.

270 NO. 279BULLETIN AMERICAN MUSEUM OF NATURAL HISTORY

further constrains the Mesilla A and Pearson Mesa faunas to the upper Gauss Chron, just priorto the Gauss/Matuyama boundary. The Mesilla B and Virden faunas occur higher in the samestratigraphic sequences as the Mesilla A and Pearson Mesa faunas, respectively, and are latestBlancan in age (2.2–1.8 Ma). Both faunas contain taxa restricted to the Blancan, including thecamels Blancocamelus and Gigantocamelus from Mesilla B, and Canis lepophagus from Vir-den. The absence of Nannippus, and of Mammuthus and other genera that first appear in theIrvingtonian, support the age.

The Tijeras Arroyo fauna from the Albuquerque basin and the Tortugas Mountain andMesilla C faunas from the Mesilla basin all possess Mammuthus and other mammals indicativeof early Irvingtonian age. The association of Mammuthus and Stegomastodon in the TortugasMountain LF indicates an age younger than 1.8 Ma, after the arrival of Mammuthus in NorthAmerica from Eurasia and before the extinction of Stegomastodon at about 1.2 Ma. The co-occurrence of Glyptotherium arizonae, Equus scotti, and the primitive mammoth M. meri-dionalis in Tijeras Arroyo and Mesilla C is typical of southwestern early Irvingtonian faunas.Fossils of M. meridionalis from Tijeras Arroyo and Mesilla C are both closely associated withdates of 1.6 Ma on pumice from the lower Bandelier tuff, making them among the oldestdated mammoths in North America. A fauna from San Antonio Mountain (SAM) Cave in theSan Luis basin of northernmost New Mexico lacks large mammals, but the presence of themicrotine rodents Mictomys kansasensis, an advanced species of Allophaiomys, Lemmiscuscurtatus, and Microtus cf. M. californicus indicates medial Irvingtonian age, between about1.0 and 0.85 Ma.

INTRODUCTION

There are 31 vertebrate fossil assemblagescurrently known from New Mexico that dateto the time interval from the early BlancanNorth American land mammal ‘‘age’’ (NAL-MA), about 4.0 Ma (early Pliocene), throughthe medial Irvingtonian NALMA, about 0.8Ma (late early Pleistocene). These faunas areconcentrated in two areas of the state, the RioGrande Valley and the Gila River Valley (fig.12.1). The Rio Grande bisects the state fromthe Colorado border on the north to the Mex-ico and Texas borders on the south, flowingthrough a series of structural basins that arepart of the Rio Grande rift system. Athrough-flowing Rio Grande apparently orig-inated sometime in the early Pliocene afterabout 5 Ma, and shortly thereafter began de-positing fluvial sediments that preserve ver-tebrate fossils. Most of the Rio Grande riftbasins contain Blancan and/or Irvingtonianvertebrate fossils, from the San Luis basin onthe Colorado border in the northernmost partof the state to the Mesilla basin on the Mex-ican border in southernmost New Mexico.The Gila River originates in the MogollonMountains in southwestern New Mexico andflows southwestward, eventually crossinginto Arizona. Blancan vertebrate faunas havebeen recovered from sediments of the GilaGroup in the Mangas basin and the Duncan

basin in the Gila River Valley in southwest-ern New Mexico (fig. 12.1). Several addi-tional Blancan faunas are known from theGila River Valley in southeastern Arizona(Galusha et al., 1984; Tomida, 1987).

Prior to the 1980s, very few of New Mex-ico’s Blancan and Irvingtonian faunas hadbeen mentioned in the literature. In their re-view of the ‘‘Pleistocene’’ mammals ofNorth America, including the Blancan, whichis now known to be entirely Pliocene, Kurtenand Anderson (1980) did not list a singleBlancan or Irvingtonian fauna from NewMexico. Tedford (1981) summarized all ofNew Mexico’s Blancan and Irvingtonian fau-nas known at that time, including 12 Blancanfaunas and 1 Irvingtonian fauna. DespiteTedford’s (1981) paper, no sites from NewMexico were mentioned in the review ofNorth American Blancan and Irvingtonianfaunas in Lundelius et al. (1987). Repenning(1987) mentioned the early Blancan Truth orConsequences Local Fauna (LF) in his re-view of late Cenozoic microtine rodents fromNorth America. We summarize all studies onNew Mexico Blancan and Irvingtonian fau-nas published since Tedford (1981) throughthe end of 2000, and include much new un-published data.

MATERIALS AND METHODSRichard Tedford’s 1981 paper on the bio-

chronology of late Cenozoic mammalian fau-

2003 271MORGAN AND LUCAS: BLANCAN AND IRVINGTONIAN MAMMALS

nas from New Mexico provided the impetusfor our long-term project to collect, docu-ment, and describe all Blancan and Irving-tonian vertebrate faunas from New Mexico.Beginning in the mid-1980s and continuingto the present, paleontologists from the NewMexico Museum of Natural History and theUniversity of New Mexico have been in-volved in a program to locate new faunas ofBlancan and Irvingtonian age throughoutNew Mexico and to recollect faunas of thisage discussed by Tedford (1981). Many newBlancan and Irvingtonian faunas have beendiscovered in New Mexico in the past 15years (Lucas and Oakes, 1986; Repenningand May, 1986; Morgan et al., 1998; Morganand Lucas, 1999, 2000a; Rogers et al., 2000),and extensive new fossil material has beenadded to many of the faunas described inTedford’s 1981 paper (Vanderhill, 1986;Tomida, 1987; Lucas et al., 1993; Morgan etal., 1997; Morgan and Lucas, 1999, 2000a,2000b). Combining the information in Ted-ford’s 1981 paper, which was based on fos-sils in the collections of the Frick Laboratoryat the American Museum of Natural History,and data obtained through our fieldwork, wecan now provide a fairly detailed review ofthe Blancan and Irvingtonian fossil record ofNew Mexico.

The present paper summarizes the histor-ical, faunal, stratigraphic, and geochronolog-ic data for all known Blancan and Irvington-ian mammalian faunas from New Mexico.Faunal lists for sites containing four or moretaxa of mammals are provided in tables 12.1and 12.2, including 15 Blancan faunas and 4Irvingtonian faunas. Numerous additionalsites with fewer than four mammals are dis-cussed in the text. We follow Woodburne(1987: xiv) for the definitions of fauna andlocal fauna. Thus, a fauna is ‘‘an assemblageof fossil vertebrates of specific taxonomiccomposition obtained from a number of geo-graphically diverse sites.’’ A local fauna is‘‘an assemblage of fossil vertebrates of spe-cific taxonomic composition recovered fromone or a few sites that are closely spacedstratigraphically and geographically.’’ Wefollow Woodburne and Swisher (1995) foruse of the age terms early, medial, and latefor subdivisions of epochs (e.g., early Plio-cene) and NALMAs (e.g., medial Blancan).

Space does not permit us to exhaustivelyreview all of the 31 currently known NewMexico Blancan and Irvingtonian faunas andsites. Detailed documentation (e.g., cataloguenumbers, morphological descriptions, andmeasurements) is not provided for specimensdescribed in previous papers. Documentationis provided for selected fossils not previouslymentioned in the literature. We give brief de-scriptions of certain fossils that are of criticalimportance to mammalian biochronology.This paper should be considered a status re-port because we are actively involved infieldwork on Blancan and Irvingtonian fau-nas throughout New Mexico. In particular,comprehensive faunal papers are planned inthe near future for the Arroyo de la Parida,Truth or Consequences, and Pearson MesaLocal Faunas, and the late Blancan and earlyIrvingtonian faunas from the Mesilla basin.

There are three major collections of Blan-can and Irvingtonian vertebrate fossils fromNew Mexico. The New Mexico Museum ofNatural History and Science (NMMNH) inAlbuquerque and the Frick Collection (F:AM) of the American Museum of NaturalHistory (AMNH) in New York both containsubstantial collections of Blancan and Irving-tonian fossils from throughout the state. TheMuseum of Arid Land Biology at the Uni-versity of Texas at El Paso (UTEP) has largecollections from the Mesilla basin in south-ern New Mexico. Other New Mexico Blan-can and Irvingtonian fossils consulted duringthis study include specimens from the Ge-ology Museum in the Department of Earthand Planetary Sciences at the University ofNew Mexico (UNM) in Albuquerque, theNew Mexico State University Museum(NMSUM) in Las Cruces, the University ofArizona Laboratory of Paleontology (UALP)in Tucson, and the United States GeologicalSurvey Collection (USGS) in Denver. Sitenumbers (preceded by NMMNH L-) listedthroughout the paper refer to NMMNH fossillocalities. Field notes, map coordinates, andother information on these sites are on file inthe Paleontology Collection at the NMMNH.

PREVIOUS WORK

Pliocene (Blancan) fossils were first re-ported from New Mexico by Needham


←

Fig. 12.1. Map of New Mexico showing the location of all late Hemphillian, Blancan, and Irving-tonian fossil sites. The structural basins are named and indicated by stippling. Sites are numbered fromnorth to south in the Rio Grande Valley (sites 1–29), followed by sites in the Gila River Valley (sites30–33). Site names and ages are listed here. See text for more detailed information on individual sites.1, San Antonio Mountain (SAM) Cave, medial Irvingtonian; 2, Puye Formation site, late Hemphillian;3, Ancha sites, late Blancan; 4, Santo Domingo, late Blancan; 5, Western Mobile, early Irvingtonian;6, Loma Colorado de Abajo, early/medial Blancan; 7, Mountainview, Blancan; 8, Tijeras Arroyo, earlyIrvingtonian; 9, Pajarito, medial Blancan; 10, Isleta, Blancan; 11, Los Lunas, Blancan; 12, Belen, medialBlancan; 13, Mesas Mojinas, Blancan; 14, Veguita, Blancan; 15, Sevilleta, Blancan; 16, Arroyo de laParida, medial Blancan; 17, Fite Ranch, early Irvingtonian; 18, Silver Canyon, Blancan; 19, ElephantButte Lake, medial Blancan; 20, Cuchillo Negro Creek, medial Blancan; 21, Truth or Consequences,early Blancan; 22, Palomas Creek, medial Blancan; 23, Hatch, medial Blancan; 24, Rincon Arroyo, lateBlancan/early Irvingtonian; 25, Tonuco Mountain, medial Blancan; 26, Tortugas Mountain, early Ir-vingtonian; 27, Mesilla A, late Blancan; 28, Mesilla B, latest Blancan; 29, Mesilla C, early Irvingtonian;30, Buckhorn, early Blancan; 31, Walnut Canyon, latest Hemphillian; 32, Pearson Mesa, late Blancan;33, Virden, latest Blancan. Map modified from Tedford (1981).

(1936), who described a pair of mandibles ofthe gomphotheriid proboscidean Rhynchoth-erium and a lower molar of the horse Plesip-pus from Santa Fe Group deposits in Arroyode la Parida, northeast of Socorro in SocorroCounty. Plesippus is now generally regardedas a primitive subgenus of Equus, and is typ-ical of Blancan faunas. Needham also re-ported several fossil turkey (Meleagris)bones from a pumice deposit of probable ear-ly Irvingtonian age in an exposure along theRio Grande near San Antonio, also in So-corro County. Denny (1940) identified Equusand the gomphotheriid proboscidean Stego-mastodon from Santa Fe Group depositsnorth of the Rio Salado on land now withinthe Sevilleta National Wildlife Refuge in thesouthernmost Albuquerque basin in northernSocorro County. Between 1926 and 1953,collectors working for the Frick Laboratoryaccumulated significant samples of Blancanand Irvingtonian vertebrates from various lo-calities throughout New Mexico. Very few ofthese specimens were published until 1981,when Tedford summarized the mammalianbiochronology of the late Cenozoic basins ofNew Mexico. Between 1926 and 1929, Jo-seph Rak collected fossil vertebrates on theSanto Domingo Reservation in the northernAlbuquerque basin, from Hot Springs (nowTruth or Consequences), Palomas Creek, andother sites west of Elephant Butte Lake inthe Engle and Palomas basins, and from theMesilla basin south of Las Cruces. CharlesFalkenbach collected fossils with Rak in

1928 from Hot Springs and in 1929 from theMesilla basin. Ted Galusha collected fossilsin 1946 from the northern edge of the IsletaReservation in southern Bernalillo County.George Pearce made collections in the Mes-illa basin in 1949 and near Buckhorn in theMangas basin in 1953.

Tedford (1981) was the first paleontologistto summarize the data on New MexicanBlancan and Irvingtonian faunas, primarilybased on the previously unpublished materialin the Frick Collection at the AMNH. Ted-ford provided a biostratigraphic frameworkfor all subsequent work on New MexicoBlancan and Irvingtonian faunas, which hasincluded additional work on many of the fau-nas he discussed, as well as the discovery ofnew faunas. Repenning and May (1986) pro-vided a faunal list, brief taxonomic descrip-tions, and magnetostratigraphy for the earlyBlancan Truth or Consequences LF from thePalomas Formation in the Palomas basinnear Truth or Consequences in Sierra Coun-ty. Lucas and Oakes (1986) described themedial Blancan Cuchillo Negro Creek LFfrom the Engle basin, also from the PalomasFormation in Sierra County. In his doctoraldissertation, Vanderhill (1986) presented adetailed review of the vertebrate paleontolo-gy, magnetostratigraphy, and lithostratigra-phy of late Blancan through early Irvington-ian faunas in the Mesilla basin south of LasCruces in Dona Ana County. Tomida (1987)provided a faunal list and magnetostratigra-phy for the late Blancan Pearson Mesa LF

274 NO. 279BULLETIN AMERICAN MUSEUM OF NATURAL HISTORYT

AB

LE

12.1

Fau

nal

Lis

tof

Bla

nca

nM

amm

als

from

New

Mex

ico

The

Bla

ncan

faun

asar

eli

sted

acro

ssth

eto

pof

the

tabl

ew

ith

asu

pers

crip

tle

tter

that

corr

espo

nds

toa

refe

renc

eor

refe

renc

esat

the

end

ofth

eta

ble

from

whi

chth

efa

unal

list

sw

ere

take

n.T

hefa

unas

are

list

edin

orde

rfr

omth

eol

dest

onth

ele

ftto

the

youn

gest

onth

eri

ght.

The

pres

ence

ofa

spec

ies

ina

faun

ais

indi

cate

dby

‘‘X

’’an

dit

sab

senc

eby

‘‘—

’’.

Spe

cies

list

edas

‘‘X

?’’

wer

ete

ntat

ivel

yid

enti

fied

(e.g

.,id

enti

fied

wit

h‘‘

cf.’’

or‘‘

?’’)

inth

eor

igin

alpu

blic

atio

ns.

Tax

am

arke

dw

ith

anas

teri

sk(*

)ar

eba

sed

onid

enti

fica

tion

sof

spec

imen

sco

llec

ted

afte

rth

eor

igin

alpa

per

onth

esi

tew

aspu

blis

hed.

Onl

yfa

unas

wit

hfo

uror

mor

eta

xaof

mam

-m

als

are

incl

uded

inth

ista

ble.

Sm

alle

rfi

nds

ofim

port

ant

Bla

ncan

taxa

are

disc

usse

din

the

text

.T

here

are

thre

edi

stin

ctbi

ostr

atig

raph

icle

vels

inth

eM

esil

laba

sin

acco

rdin

gto

Van

derh

ill

(198

6);

the

mam

mal

sfr

omhi

sF

auna

Aof

late

Bla

ncan

age

and

Fau

naB

ofla

test

Bla

ncan

age

are

list

edbe

low

.F

auna

Cof

earl

yIr

ving

toni

anag

eis

list

edin

tabl

e12

.2.

2003 275MORGAN AND LUCAS: BLANCAN AND IRVINGTONIAN MAMMALST

AB

LE

12.1

(Con

tinu

ed)

276 NO. 279BULLETIN AMERICAN MUSEUM OF NATURAL HISTORYT

AB

LE

12.1

(Con

tinu

ed)

2003 277MORGAN AND LUCAS: BLANCAN AND IRVINGTONIAN MAMMALST

AB

LE

12.1

(Con

tinu

ed)


TABLE 12.2Faunal List of Irvingtonian Mammals from New Mexico

Irvingtonian faunas are listed across the top of the table with a superscript letter that corresponds to references atthe end of the table. Tijeras Arroyo, Tortugas Mountain, and Mesilla Basin Fauna C are early Irvingtonian in age,

and SAM Cave is medial Irvingtonian. The presence of a species in a fauna is indicated by ‘‘X’’ and its absence by‘‘—’’. Species listed as ‘‘X?’’ were tentatively identified (e.g., identified with ‘‘cf.’’ or ‘‘?’’) in original publications.Taxa marked with an asterisk (*) are based on identifications of specimens collected after the original paper on thesite was published. Only faunas with four or more mammal taxa are included. Smaller finds of important Irving-

tonian taxa are discussed in the text.


TABLE 12.2(Continued)


from the Gila Group in the Duncan basin inHidalgo County. Lucas et al. (1993) re-viewed late Blancan and early Irvingtonianvertebrate faunas from Tijeras Arroyo in theAlbuquerque basin near Albuquerque in Ber-nalillo County. Lucas and Morgan (1996) re-ported the gomphothere Rhynchotherium fal-coneri, and briefly summarized the remain-der of the mammalian fauna, from the medialBlancan Arroyo de la Parida LF from the So-corro basin in Socorro County. Morgan et al.(1997) described the latest Hemphillian Wal-nut Canyon LF and the early Blancan Buck-horn LF from the Gila Group in the Mangasbasin in Grant County. Morgan et al. (1998)reviewed the medial Blancan Tonuco Moun-tain LF from the Camp Rice Formation inthe Jornada basin north of Las Cruces inDona Ana County. Hawley et al. (1969) andLucas et al. (1999, 2000) discussed early Ir-vingtonian proboscideans and horses fromgravel pits in the vicinity of Tortugas Moun-tain east of Las Cruces in the northern partof the Mesilla basin. Morgan and Lucas(1999, 2000a) reviewed 10 Blancan and 2Irvingtonian faunas from the Albuquerquebasin. Morgan and Lucas (2000b) described2 late Blancan faunas from Pearson Mesa inthe Duncan basin. Rogers et al. (2000) de-scribed the Irvingtonian vertebrate faunafrom San Antonio Mountain (SAM) Cavefrom the San Luis basin in northernmostNew Mexico.

CHRONOLOGY

We follow Berggren et al. (1995) forplacement of the Miocene/Pliocene and Pli-ocene/Pleistocene boundaries and their sub-divisions, and for the boundaries of the geo-magnetic chrons and subchrons. The Mio-cene/Pliocene boundary is 5.32 Ma, and thePliocene/Pleistocene boundary is locatednear the top of the Olduvai Subchron at 1.81Ma. The Pliocene is subdivided into the earlyand late Pliocene, with the boundary betweenthese subdivisions placed at the boundarybeween the Gilbert and Gauss Chrons at 3.58Ma. The Pleistocene is subdivided into theearly, medial, and late Pleistocene. Theboundary between the early and medialPleistocene is the boundary beween the Ma-tuyama and Brunhes Chrons at 0.78 Ma. The

beginning of the late Pleistocene at 0.13 Mais defined by the onset of the last (Sanga-monian) interglacial.

Lindsay et al. (1984) and Tedford et al.(1987) placed the boundary between theHemphillian and Blancan NALMAs in theearly Pliocene at about 4.5 Ma. Lundelius etal. (1987) stated that this boundary was notwell dated, but fell in the interval of about4.4 to 4.0 Ma. Repenning (1987) consideredthe Hemphillian/Blancan boundary to besomewhat earlier (about 4.8 Ma) based onthe arrival from the Old World of the im-migrant microtine rodents Mimomys and Ne-braskomys. The end of the Hemphillian ischaracterized by a major extinction event, in-cluding the disappearance of the familiesRhinocerotidae and Protoceratidae, the hors-es Hipparion, Neohipparion, Pseudhippa-rion, Astrohippus, and Dinohippus, and thecarnivores Agriotherium, Machairodus, andPlesiogulo.

Lindsay et al. (1984) discussed severalmammalian genera that appeared at the be-ginning of the Blancan, including the volePliophenacomys and the pocket gopher Geo-mys, and also listed a number of genera thatappeared in a relatively short interval in theearly Blancan at about 3.7 Ma (their Trigon-ictis appearance datum), including: the rab-bits Nekrolagus and Pratilepus; the rodentsNeotoma and Pliopotamys; the carnivoresChasmaporthetes, Trigonictis, and Ursus; thepeccary Platygonus; the camel Camelops;and the deer Bretzia. Lundelius et al. (1987),Tedford et al. (1987), and Woodburne andSwisher (1995) defined the beginning of theBlancan using most of the same genera men-tioned by Lindsay et al. (1984) and Repen-ning (1987), in particular Old World immi-grants such as Mimomys, Nebraskomys,Chasmaporthetes, Trigonictis, Ursus, Bret-zia, and Odocoileus. However, according tosome authors (e.g., Lindsay et al., 1984; Cas-siliano, 1999), the earliest occurrences of cer-tain of these genera are actually well abovethe Hemphillian/Blancan boundary, spanningan interval in the early Blancan betweenabout 4.5 and 3.7 Ma. Cassiliano (1999) sug-gested that the first appearance of Sigmodonin the Anza-Borrego Desert sequence insouthern California at about 4.3 Ma may ap-proximate the Hemphillian/Blancan bound-


ary. Mou (1999) documented the earliest ap-pearance of Blancan mammals from the Pan-aca LF in Nevada at about 4.95 Ma. Theabove discussion indicates that the Hemphil-lian/Blancan boundary is not well dated, butcan be placed in the time range of about 4.9to 4.3 Ma.

Tedford (1981) divided the Blancan intothree intervals: early Blancan (4.5–3.7 Ma),medial Blancan (3.7–2.5 Ma), and late Blan-can (2.5–1.5 Ma). Repenning (1987) dividedthe Blancan into five intervals (Blancan I–V)based on the biochronology of microtine (5arvicoline) rodents. Repenning’s system isdependent on the presence of microtines in afauna to determine its age, so in many casesit has limited utility. Only one Blancan faunafrom New Mexico, the Buckhorn LF inGrant County (Morgan et al., 1997), containsmicrotine rodents. Woodburne and Swisher(1995) recognized only two subdivisions ofthe Blancan, early Blancan (4.9–2.7 Ma) andlate Blancan (2.7–1.8 Ma), with the bound-ary between the early and late Blancan cor-responding to the beginning of the GreatAmerican Interchange at about 2.7 Ma. Ted-ford’s (1981) subdivisions of the Blancan arethe most useful for New Mexico faunas, withslight modifications as follows: early Blan-can (4.5–3.6 Ma)—upper boundary corre-sponds to the Gilbert/Gauss boundary andthe Trigonictis appearance datum of Lindsayet al. (1984); medial Blancan (3.6–2.7 Ma)—upper boundary corresponds to the beginningof the Great American Interchange, which isjust slightly below the Gauss/Matuyamaboundary; late Blancan (2.7–1.8 Ma)—upperboundary corresponds to the Plio-Pleistoceneboundary, the top of the Olduvai Subchron,and the first appearance of Mammuthus.

Lundelius et al. (1987) documented a tran-sitional interval between the Blancan and Ir-vingtonian, from about 2.2 to 1.8 Ma. Mostcharacteristic Blancan mammalian genera,such as Borophagus, Hypolagus, Paenemar-mota, Equus (Plesippus), Nannippus, andRhynchotherium, became extinct by about2.2 Ma (the Nannippus extinction datum ofLindsay et al., 1984). Lundelius et al. definedthe Irvingtonian on the first appearance ofLepus, Microtus, Smilodon, Equus (Equus),Euceratherium, and Mammuthus, most ofwhich did not appear until after 1.8 Ma. Cas-

siliano (1999) evaluated the biostratigraphicrecord for most of these genera and conclud-ed that none were suitable for defining theBlancan/Irvingtonian boundary. He tenta-tively placed the Blancan/Irvingtonianboundary in the latest Pliocene between 2.15and 1.95 Ma. The first appearance of Mam-muthus is often used to define the Irvington-ian; however, all well-dated mammoths fromNorth America are younger than 1.8 Ma (Lu-cas, 1995, 1996; Cassiliano, 1999), and arethus slightly younger than the Plio-Pleisto-cene boundary.

The first appearance of immigrants fromoutside of North America is generally con-sidered to be of utmost importance in estab-lishing boundaries between North Americanland-mammal ages (Lundelius et al., 1987;Woodburne, 1996). Thus, the appearance ofMammuthus would seem to be the most log-ical time to establish the Blancan/Irvington-ian boundary, roughly corresponding to thePliocene/Pleistocene boundary at about 1.8Ma. Mammuthus may not be the ideal genusto define the beginning of the Irvingtonian(e.g., Cassiliano, 1999), but mammoths dooccur in all three early Irvingtonian faunasfrom New Mexico. For purposes of our dis-cussion, we will use the first appearance ofMammuthus to define the beginning of theIrvingtonian at about 1.8 Ma. Lundelius etal. (1987) used a three-part subdivision of theIrvingtonian: early Irvingtonian (1.8–1.0Ma), medial Irvingtonian (1.0–0.6 Ma), andlate Irvingtonian (0.6–0.3 Ma). The bound-ary between the Irvingtonian and Ranchola-brean corresponds to the first appearance ofBison at about 0.3 Ma. Repenning (1987)subdivided the Irvingtonian into two inter-vals (Irvingtonian I and II) based on micro-tine biochronology, and placed the boundarybetween the Irvingtonian and Rancholabreanslightly earlier, at 0.4 Ma. We follow Lun-delius et al. (1987) in recognizing the early,medial, and late Irvingtonian, and the place-ment of the Irvingtonian/Rancholabreanboundary at 0.3 Ma.

BLANCAN AND IRVINGTONIANVERTEBRATE FAUNAS FROM

NEW MEXICOThere are 24 Blancan and 7 Irvingtonian

vertebrate fossil assemblages currently


known from New Mexico (fig. 12.1). Theserange from sites with a single species ofmammal to 26 species of mammals in SAMCave. All 31 of these assemblages are dis-cussed below, but only those faunas withfour or more species of mammals (15 Blan-can and 4 Irvingtonian faunas) are listed intables 12.1 and 12.2. Twenty-eight of theseassemblages (21 Blancan and 7 Irvingtonian)are in the Rio Grande Valley and 3 Blancanfaunas are in the Gila River Valley in south-western New Mexico. The discussion of fau-nas generally proceeds from north to south,with the Rio Grande Valley sites followed bythe Gila River Valley sites. All sites men-tioned in the text and the structural basins inwhich they occur are indicated on the mapin figure 12.1.

SAN LUIS BASIN

SAN ANTONIO MOUNTAIN (SAM) CAVE:San Antonio Mountain (SAM) Cave is lo-cated in the San Luis basin about 10 kmsouth of the Colorado border and 7 km north-west of San Antonio Mountain in Rio ArribaCounty in northernmost New Mexico (fig.12.1, site 1). Several factors distinguish SAMCave from all other Blancan and Irvington-ian localities in New Mexico, in particular,its mode of occurrence and high elevation(Rogers et al., 2000). SAM Cave is a lavatube formed in the Pliocene Servilleta Basalt,and the fossils occur in locally derived cavesediments. All other sites discussed in thispaper are derived from alluvial, fluvial, orlacustrine sediments associated with the an-cestral Rio Grande or Gila Rivers. SAMCave is also considerably higher in elevation(2737 m) than any other Blancan or Irving-tonian site in New Mexico. Eleven localizedsites within SAM Cave have produced ver-tebrate fossils, 10 of which are medial Ir-vingtonian in age (NMMNH sites L-4385–4390, 4392–4395) and 1 of which is Ran-cholabrean (NMMNH site L-4381). Amongthe medial Irvingtonian sites, there appearsto be a range of ages from about 1.0 Ma tojust after the Matuyama/Brunhes boundary at0.78 Ma (Rogers et al., 2000). In table 12.2and in the following discussion, we have ar-bitrarily combined the nine medial Irvington-ian sites in Rogers et al. (2000, table 2) that

date to the late Matuyama Chron, after theJaramillo Subchron and before the Matuya-ma/Brunhes boundary (between about 1.0and 0.78 Ma). A 10th fauna (NMMNH siteL-4385) occurs in normally magnetized sed-iments of the Brunhes Chron, but is not in-cluded here because it contains no species ofmammals not found in the older sites.

The combined vertebrate assemblage fromthe nine medial Irvingtonian sites in SAMCave includes a minimum of 41 species (fau-nal list from Rogers et al., 2000, completelist of mammals in table 2): one species oftrout; 2 species of amphibians, tiger sala-mander (Ambystoma tigrinum), and chorusfrog (Pseudacris triseriata); 3 reptiles,horned lizard (Phrynosoma douglassii), rat-tlesnake (Crotalus viridis), and garter snake(Thamnophis elegans); 9 birds, short-earedowl (Asio cf. A. flammeus), least grebe(Tachybaptus cf. T. dominicus), vireo (Vireosp.), chickadee (Parus sp.), junco (Juncosp.), savannah sparrow (Passerculus cf. P.sandwichensis), sparrow (Ammodramus),and 2 wood warblers (Family Parulidae); and26 species of mammals, including a shrew, abat, 5 carnivores, 2 lagomorphs, and 17 ro-dents. The SAM Cave vertebrate assemblageis dominated by small species, and thus it isvery difficult to make comparisons with oth-er New Mexico Irvingtonian faunas, whichare composed primarily of large mammals.Therefore, comparisons are mostly with Ir-vingtonian small mammal faunas outside ofNew Mexico, in particular, Hansen Bluff, lo-cated about 40 km northeast of SAM Cavein southern Colorado (Rogers et al., 1992).The only larger mammals in SAM Cave arethe badger Taxidea taxus and the wolf Canisrufus. However, the identification of C. rufusfrom Sam Cave is questionable, and it ismore likely to be the Irvingtonian wolf C.armbrusteri (see Berta, 1995).

The age of the SAM Cave vertebrate as-semblage is determined primarily by the bio-chronology of its extensive microtine (5 ar-vicoline) rodent fauna (Rogers et al., 2000).The presence of the microtines Mictomyskansasenis, Allophaiomys, Lemmiscus cur-tatus, and Microtus cf. M. californicus helpsdate the oldest sites in SAM Cave. The firstappearance of M. kansasenis is in the lateearly Irvingtonian Sappa Fauna of Nebraska


(1.3 Ma; Martin and Schultz, 1985). Thepresence of an advanced unnamed species ofAllophaiomys indicates an age greater than0.85 Ma, based on comparisons with thenearby Hansen Bluff fauna (Repenning,1992; Rogers et al., 2000). SAM Cave ap-parently documents the evolution of thesagebrush vole Lemmiscus from Allophaiom-ys between about 1.0 and 0.85 Ma (Rogerset al., 2000). The occurrence of Microtus cf.M. californicus indicates that the fauna isyounger than the beginning of the JaramilloSubchron (1.07 Ma; Repenning, 1992). Thered-backed vole Clethrionomys first appearsin two SAM Cave sites that date from 0.85Ma to just above the Matuyama/Brunhesboundary. The occurrences of Clethrionomysand Lemmiscus in SAM Cave represent theoldest records of these genera in NorthAmerica (Rogers et al., 2000).

The presence of Mictomys kansasenis, Al-lophaiomys, Lemmiscus curtatus, and Micro-tus cf. M. californicus in SAM Cave indi-cates an age range between about 1.0 Ma and0.85 Ma (Rogers et al., 2000), which placesthis fauna in the early part of the medial Ir-vingtonian. A slightly younger medial Ir-vingtonian site in SAM Cave contains Cleth-rionomys, and is between 0.85 and 0.78 Main age. SAM Cave is younger than other Ir-vingtonian faunas known from New Mexico,including Tijeras Arroyo, Tortugas Moun-tain, and Mesilla Basin Fauna C, all of whichare early Irvingtonian.

ESPANOLA BASIN

ANCHA SITES: Blancan mammals areknown from two sites in the southernmostEspanola basin southwest of Santa Fe in San-ta Fe County (fig. 1, site 3). These two sitesrepresent the northernmost occurrences ofBlancan mammals in New Mexico. A vol-caniclastic unit correlative with the AnchaFormation, exposed in an abandoned cinderquarry near the Santa Fe Airport (NMMNHsite L-3116), preserves a trackway(NMMNH 25583) of a large camelid, eitherCamelops or one of the giant Blancan camels(e.g., Gigantocamelus). The camel tracks oc-cur in a fine-grained volcaniclastic depositthat is part of the Cerros del Rio volcanicfield, dated to between 2.8 and 2.3 Ma (Kon-

ing et al., 2001). In 1999, at a second siteabout 10 km farther south and about 2 kmwest of Turquoise Hill (NMMNH site L-4321), Dan Koning collected a mandiblewith p4–m3 (NMMNH 30493) of the prairiedog Cynomys in a sandy unit about 6 m be-low the local top of the Ancha Formation. Ina review of the fossil history of prairie dogs,Goodwin (1995) noted that the earliest fossilrecord of the genus Cynomys is late Blancan.The mandible from the Ancha Formationmost closely resembles the extinct species C.hibbardi from the late Blancan White RockLF in Kansas (Eshelman, 1975).

ALBUQUERQUE BASIN

The Albuquerque basin has often been di-vided into two separate basins or subbasins,with the northern third called the Santo Do-mingo basin and the southern two-thirdscalled the Albuquerque-Belen basin (e.g.,Tedford, 1981). We follow a more recenttrend, which is to combine these basins andrefer to them as the Albuquerque basin. Wearbitrarily divide the Albuquerque basin intonorthern and southern portions, with the di-viding line being the boundary between Ber-nalillo and Valencia counties. The Plioceneand Pleistocene stratigraphic units in the Al-buquerque basin that are known to containBlancan and Irvingtonian vertebrate fossilsinclude the Ceja and Loma Barbon membersof the Arroyo Ojito Formation of Connell etal. (1999) and the Sierra Ladrones Forma-tion. The stratigraphy of Pliocene and Pleis-tocene geologic units in the Albuquerque ba-sin is currently in a state of flux, and thus itis likely that some of the stratigraphic namesrecognized here may change in the next fewyears.

SANTO DOMINGO: The Santo Domingo LF(fig. 12.1, site 4) was derived from axial rivergravels of the Sierra Ladrones Formation(Smith and Kuhle, 1998), east of the RioGrande near the Santo Domingo Pueblo inSandoval County (Tedford, 1981). Tedfordidentified the horses Equus calobatus and E.scotti from the Santo Domingo fauna, bothof which are known from the late Blancanand early Irvingtonian. Recent examinationof fossils from Santo Domingo in the FrickCollection revealed two additional taxa, the


small three-toed horse Nannippus peninsu-latus and the large peccary Platygonus cf. P.bicalcaratus, both of which are indicative ofBlancan faunas. The presence of Nannippussuggests an age of 2.2 Ma or older. Tedfordnoted that these deposits are interbeddedwith the Santa Ana Mesa basalts, dated at2.67 Ma and 2.41 Ma (Smith and Kuhle,1998), and are overlain by the lower Ban-delier Tuff dated at 1.61 Ma (Izett and Ob-radovich, 1994). The biostratigraphic andgeochronologic constraints indicate an agebetween 2.7 and 2.2 Ma for the Santo Do-mingo LF.

WESTERN MOBILE: Two species of mam-mals are known from the Western Mobilegravel pit (NMMNH Site L-1546; fig. 12.1,site 5), located about 3 km northeast of Ber-nalillo in Sandoval County (Lucas et al.,1993; Morgan and Lucas, 2000a). These fos-sils, including glyptodont scutes and a pro-boscidean tusk fragment, were collected asfloat and thus lack precise stratigraphic prov-enance, although they were almost certainlyderived from the Sierra Ladrones Formation.The most diagnostic fossils from the WesternMobile site are five well-preserved interiorcarapacial osteoderms of the glyptodontGlyptotherium arizonae. These osteodermsare identified as G. arizonae on the basis oftheir large size, comparatively great thick-ness, and small, flat central figure (Gilletteand Ray, 1981). G. arizonae also occurs inthe early Irvingtonian Tijeras Arroyo fauna,located about 30 km south (see below). Mostother published records of G. arizonae fromthe southwestern United States are early Ir-vingtonian in age, including Gilliland andRock Creek in Texas, Holloman inOklahoma (Gillette and Ray, 1981), andMesilla Basin Fauna C from the Mesilla ba-sin in southernmost New Mexico (Vander-hill, 1986). This glyptodont is also knownfrom two latest Blancan sites in New Mexi-co, Mesilla Basin Fauna B and the VirdenLF in the Duncan basin in the southwesternpart of the state (Morgan and Lucas, 2000b).The Western Mobile glyptodont scutes arealso significant because the location of thegravel pit at about 358209 North latitude rep-resents one of the northernmost records forthe genus Glyptotherium in North America(Gillette and Ray, 1981).

LOMA COLORADO DE ABAJO: Loma Colo-rado de Abajo is a prominent hill within thecity limits of Rio Rancho in Sandoval Coun-ty, about 20 km northwest of Albuquerque inthe northern Albuquerque basin (fig. 12.1,site 6). Between 1990 and 1996, Paul Knightcollected several skulls of small rodents fromindurated, fine-grained reddish sandstonesnear the base of the exposed section on thesouth-facing escarpment of Loma Coloradode Abajo (NMMNH Site L-1462). The fos-siliferous level is in the Loma Barbon Mem-ber in the upper part of the Arroyo Ojito For-mation of Connell et al. (1999), about 8 mbelow the base of the overlying Ceja Mem-ber of the same formation. The Loma Colo-rado de Abajo LF consists of just three taxa(Morgan and Lucas, 1999, 2000a), a smallland tortoise and two genera of rodents,Spermophilus and Geomys. The same stra-tum from which the rodent fossils were col-lected also contains numerous ichnofossilsthat appear to be rodent burrows. The LomaColorado de Abajo LF is unique among NewMexico Blancan faunas in consisting entirelyof small burrowing vertebrates.

A ground squirrel of the genus Spermo-philus is represented in the Loma Coloradode Abajo LF by a partial skull with P4 froma small species in the size range of living S.tridecemlineatus. It is considerably smallerthan Spermophilus cf. S. bensoni from theBlancan of southeastern Arizona (Tomida,1987), a species tentatively identified fromthe early Blancan Buckhorn LF in south-western New Mexico (Morgan et al., 1997).The Loma Colorado Spermophilus skull isalso smaller than S. pattersoni and S. ma-tachicensis from the late Hemphillian Ye-pomera Fauna in northern Mexico (Wilson,1949; Lindsay and Jacobs, 1985). Threespecimens from Loma Colorado de Abajoare provisionally referred to the primitivepocket gopher, Geomys (Nerterogeomys) mi-nor, including a nearly complete skull, a ros-trum with a complete dentition, and an eden-tulous left mandible. The two skulls are iden-tified as Geomys on the basis of their bisul-cate upper incisors, unrooted cheek teeth,and absence of enamel on the posterior sur-face of P4. Earlier pre-Blancan geomyidssuch as Pliogeomys have rooted cheek teeth.The fragmentary mandible lacks cheek teeth,


but can be identified as a member of the ex-tinct subgenus Geomys (Nerterogeomys) bythe placement of the mental foramen ventralto the masseteric crest (Tomida, 1987). Geo-mys (Nerterogeomys) first appears in the ear-ly Blancan and becomes extinct in the earlyIrvingtonian. The Loma Colorado pocket go-pher skulls are smaller than most describedskulls of Geomys (Nerterogeomys), and com-pare most closely to the small species, G.minor, known from the early Blancan Rex-road Fauna in Kansas and Verde LF in Ari-zona, and the medial Blancan Beck RanchLF in Texas and Benson Fauna in Arizona(Hibbard, 1967; Dalquest, 1978; Czaplewski,1990). Repenning and May (1986) reportedG. minor from the early Blancan Truth orConsequences LF from the Palomas Forma-tion in Sierra County in central New Mexico.The Loma Colorado mandible is smaller thanpocket gopher mandibles from the Pajaritoand Belen faunas in the Albuquerque basinreferred to G. (Nerterogeomys) paenebursar-ius (see Morgan and Lucas, 2000a). Thesmaller species of G. (Nerterogeomys) thatare most similar in size to the Loma Colo-rado Geomys (e.g., G. minor) are restrictedto the Blancan, whereas the species that sur-vive into the Irvingtonian (e.g., G. anzensis,G. garbanii, and G. persimilis) are larger.

The age of the Loma Colorado de AbajoLF is probably early or medial Blancan.Small species of Geomys (Nerterogeomys),such as G. minor, are typical of faunas ofthis age. Also, the medial to late Blancan(older than 2.2 Ma) Mountainview LF isknown from the Ceja Member of the ArroyoOjito Formation in Tijeras Arroyo, a unit thatoverlies the Loma Barbon Member. TheLoma Colorado de Abajo LF is stratigraph-ically below and thus older than the Blancanfauna from Tijeras Arroyo. However, thesetwo faunas have no taxa in common, so moredetailed biostratigraphic comparisons are notpossible.

MOUNTAINVIEW: Most of the vertebratefossils from Tijeras Arroyo, located justsouth of the Albuquerque International Air-port in Bernalillo County, are derived fromthe Sierra Ladrones Formation and are earlyIrvingtonian in age (Lucas et al., 1993; seebelow). However, one locality (NMMNHSite L-1458) at the base of the exposed strati-

graphic section in Tijeras Arroyo (fig. 12.1,site 7) has produced two species that are in-dicative of a Blancan age. This site is herenamed the Mountainview Local Fauna toeliminate any confusion with the younger Ti-jeras Arroyo Irvingtonian sites. The fossilsfrom the Mountainview site were derivedfrom a sandstone comprising unit 1 in thestratigraphic section of Lucas et al. (1993).The lowermost part of the section in TijerasArroyo, including unit 1, was referred to theCeja Member of the Arroyo Ojito Formationby Connell et al. (1999).

Lucas et al. (1993) referred a partial man-dible with p3 from Mountainview to the rab-bit Hypolagus cf. H. gidleyi. This rabbit isfound in late Hemphillian and Blancan fau-nas, but is unknown from the Irvingtonian(White, 1987). The horse Equus cf. E. cum-minsii was identified from this site based ona partial skull with a nearly complete denti-tion and several associated postcranial ele-ments (Lucas et al., 1993). E. cumminsii oc-curs in several medial and late Blancan sitesin Texas, but is unknown from the Irvington-ian (Kurten and Anderson, 1980). There aretwo other Blancan records of E. cumminsiifrom New Mexico, the medial Blancan Ar-royo de la Parida LF in Socorro County(Tedford, 1981; Lucas and Morgan, 1996)and the late Blancan Pearson Mesa LF in Hi-dalgo County (Morgan and Lucas, 2000b).

Both mammals from the Mountainviewsite in the lower portion of the Tijeras Arroyosection, Hypolagus cf. H. gidleyi and Equuscf. E. cumminsii, are typical of Blancan fau-nas, and do not occur in the Irvingtonian.The extinction in the late Pliocene of severalcharacteristic Blancan genera (the Nannippusextinction event of Lindsay et al. 1984), in-cluding Hypolagus, indicates that the Moun-tainview site is older than 2.2 Ma. Equus cf.E. cumminsii is absent from early Blancanfaunas (Kurten and Anderson, 1980). Thesetwo species suggest that Mountainview ismedial to late Blancan in age (between 3.6and 2.2 Ma). The absence of Guaje Pumicefrom the Ceja Member of the Arroyo OjitoFormation in the lower part of the TijerasArroyo section indicates that these beds pre-date deposition of the Bandelier Tuff at 1.6Ma (Lucas et al., 1993).

TIJERAS ARROYO: Ten localities in Tijeras


Arroyo (fig. 12.1, site 8) have produced asignificant vertebrate fauna (table 12.2) ofearly Irvingtonian age (Lucas et al., 1993;Morgan and Lucas, 2000a). More than 75 mof the Sierra Ladrones Formation is exposedin Tijeras Arroyo, consisting of sandstones,pumiceous sandstones, and gravels, with mi-nor amounts of mudstone and diatomite.These sediments represent axial river depos-its of an ancestral Rio Grande. The most im-portant lithological marker in these beds isthe presence of reworked Guaje Pumice de-rived from the Bandelier Tuff, Ar/Ar datedat 1.61 Ma (Izett and Obradovich, 1994), inthe units associated with an Irvingtonian fau-na (units 6–8 of Lucas et al., 1993). An ex-tensive flora of leaves and pollen from a lo-calized volcanic ash bed was collected in theTijeras Arroyo section (NMMNH Site L-1445). The Tijeras Arroyo flora indicates thatthe cottonwood forest or bosque currentlyfound along the banks of the Rio Grande inNew Mexico dates back to the early Pleis-tocene (Knight et al., 1996).

The land tortoise Hesperotestudo and fivespecies of mammals, including Glyptother-ium cf. G. arizonae, Equus scotti, Equus sp.,Camelops sp., and Mammuthus meridionalisoccur together in the Tijeras Arroyo sectionabove the Mountainview Blancan site dis-cussed above (Lucas et al., 1993; Morganand Lucas, 2000a). These species constitutea fairly typical fauna of early Irvingtonianage. Three additional species of mammals, asmall species of Equus, the llama Hemiauch-enia macrocephala and the mammoth Mam-muthus imperator, occur somewhat higher inthe Tijeras Arroyo section than the remainderof the fauna, but probably are Irvingtonianage as well.

A caudal osteoderm of a glyptodont fromTijeras Arroyo (Lucas et al., 1993) probablyis not diagnostic at the species level, al-though this specimen almost certainly rep-resents Glyptotherium arizonae. Tentative re-ferral of this osteoderm to G. arizonae is rea-sonable as its association with Mammuthusrules out a Blancan age, and the Ranchola-brean G. floridanum is restricted to the At-lantic and Gulf coastal plains (Gillette andRay, 1981). The large horse Equus scotti isthe most common mammal in the Tijeras Ar-royo Irvingtonian fauna, represented by man-

dibles, isolated teeth, and postcranials (Lucaset al., 1993; Morgan and Lucas, 2000a). E.scotti is the typical large horse in late Blan-can and early Irvingtonian faunas in thesouthwestern United States (Hibbard andDalquest, 1966), and occurs in medial Blan-can through early Irvingtonian faunas inNew Mexico (Tedford, 1981; Morgan et al.,1998). A complete equid metacarpal from Ti-jeras Arroyo is more slender than metacar-pals of E. scotti, and represents a second,smaller species of Equus (Hibbard and Dal-quest, 1966; Harris and Porter, 1980). A par-tial skull of a small Equus occurs higher inthe Tijeras Arroyo section.

Lucas and Effinger (1991) and Lucas et al.(1993) referred a mandible with left and rightm3 from Tijeras Arroyo to the primitivemammoth Mammuthus meridionalis on thebasis of its low plate count and extremelythick enamel. This is one of only two recordsof mammoths from New Mexico referred toM. meridionalis, indicating that this fauna isalmost certainly early Irvingtonian. The oth-er record consists of several partial teeth, ten-tatively referred to M. meridionalis, from anearly Irvingtonian fauna in the Mesilla basin(Vanderhill, 1986). Lucas et al. (1993) re-ferred a left M3 in a maxillary fragment fromTijeras Arroyo to the mammoth Mammuthusimperator. The teeth of M. imperator aremore advanced than M. meridionalis in hav-ing a higher plate count, higher lamellar fre-quency, and thinner enamel. The M. impe-rator specimen was found about 12 m higherin the section than the remainder of the Ti-jeras Arroyo fauna, and thus is somewhatyounger, although an Irvingtonian age is stilllikely (Lucas et al., 1993).

The presence of mammoths in unit 6 andabove clearly establishes an Irvingtonian agefor the upper part of the Tijeras Arroyo sec-tion, as Mammuthus is one of the defininggenera for the Irvingtonian NALMA. Thefirst appearance of Mammuthus in the NewWorld occurred sometime in the early Pleis-tocene (early Irvingtonian) between about1.8 and 1.6 Ma. The mammoth jaws fromTijeras Arroyo represent one of the oldestwell-documented records of Mammuthusfrom North America, based on an Ar/Ar dateof 1.61 Ma on Guaje Pumice from the SierraLadrones Formation in Tijeras Arroyo (Lu-


cas et al., 1993; Izett and Obradovich, 1994;Lucas, 1995, 1996). Although the pumicedate provides a maximum age for this site,evidence from other pumice deposits of ex-actly the same age farther south in the RioGrande Valley (Mack et al., 1996, 1998) in-dicates that the pumice is very close in ageto the fossils. The association of M. meri-dionalis with Glyptotherium arizonae andEquus scotti is indicative of an early Irving-tonian age for the Tijeras Arroyo fauna. Cor-relative early Irvingtonian faunas include theTortugas Mountain LF (Lucas et al., 1999,2000) and Mesilla Basin Fauna C (Vander-hill, 1986) from the Mesilla basin in southernNew Mexico, Gilliland in Texas (Hibbardand Dalquest, 1966), and Holloman inOklahoma (Dalquest, 1977).

PAJARITO: The Pajarito LF is located alongthe eastern escarpment of the Rio Puerco insouthern Bernalillo County, extending fromthe Pajarito land grant to the northern end ofthe Isleta Reservation (fig. 12.1, site 9). Thissite was discovered in 1946 by Ted Galusha,Frick Laboratory, who collected a small sam-ple of vertebrate fossils from just south ofthe northern boundary of the Isleta Reser-vation. According to Galusha’s field notes(copy kindly provided by Richard Tedford),he found fossils in two distinct units, a lowerunit with ‘‘potato-shaped’’ concretions and apinkish sandy unit about 5 m higher in thesection. We recently collected additional fos-sils from these same two units on the Pajaritoland grant just north of the Isleta Reservationboundary. Maldonado and Atencio (1998)placed both the concretionary bed and thepink sand in their ‘‘silt, sand, and clay lith-ofacies of the Isleta Reservation.’’ A pumicethat occurs between the two fossil-bearingunits has been Ar/Ar dated at 3.12 6 0.10Ma (Maldonado et al., 1999). Tedford (1981)called this the Laguna site and attributed itto the Ceja Member, which was recentlyplaced in the Arroyo Ojito Formation (Con-nell et al., 1999). Morgan and Lucas (2000a)renamed the Laguna site the Pajarito LF toeliminate any confusion regarding its loca-tion.

The Pajarito LF consists of eight speciesof vertebrates: a turtle, a bird, and six speciesof mammals, including three rodents, twocamels, and a deer (table 12.1). The most

diagnostic fossils are two pocket gophermandibles referred to the extinct subgenusGeomys (Nerterogeomys). The Pajarito man-dibles are similar in size and morphology toa Geomys mandible from the Belen Fauna(see below), all three of which are tentativelyreferred to Geomys (Nerterogeomys) paene-bursarius, a species originally describedfrom the late Blancan Hudspeth LF and RedLight LF in southwestern Texas (Strain,1966; Akersten, 1972). A humerus of theground squirrel Spermophilus and two rodentjaws with incisors but lacking cheek teeth arealso known from the Pajarito LF. The rodentjaws represent a smaller species than Geomysor Spermophilus, but cannot be identifiedfurther pending the discovery of specimenswith cheek teeth. The camelids from Pajaritorepresent two species, including an M3 re-ferred to the common Blancan llama, Hem-iauchenia cf. H. blancoensis, and a carpalfrom a larger camel, probably Camelops. Anunidentified cervid is represented by a partialantler. Fossils occur in both the concretion-ary bed, which is just below the pumice dat-ed at 3.12 Ma (Maldonado et al., 1999), andin the pink sand, which is just above the dat-ed pumice. One of the two Geomys mandi-bles was collected from the concretionarybed and the other from the pink sand. Thesetwo specimens are indistinguishable, sug-gesting that these two units are similar inage. The radioisotopic date of 3.1 Ma indi-cates a medial Blancan age for the PajaritoLF. This age is in agreement with the evo-lutionary grade of the Geomys mandibles andwith the absence of South American immi-grant mammals, which first appear in NorthAmerican faunas about 2.7 Ma. This siteholds significant potential for new discover-ies, as only a small amount of the exposedoutcrop has been explored for fossils.

ISLETA: In 1999, Dave Love collected anearly complete metacarpal of a small ca-melid on the east side of the Rio Grande,about 3 km northeast of the Isleta Pueblo(fig. 12.1, site 10), from strata that are prob-ably correlative with the Arroyo Ojito For-mation of Connell et al. (1999). The fossilwas derived from a unit stratigraphically be-low the pumice-bearing sands of the SierraLadrones Formation that contain early Ir-vingtonian mammals in Tijeras Arroyo, lo-


cated about 10 km to the north. This speci-men is referable to the genus Hemiauchenia,but is considerably smaller than metacarpalsof the typical Blancan species, H. blancoen-sis, known from several other Blancan faunasin New Mexico (e.g., a complete metacarpalfrom the medial Blancan Tonuco MountainLF), as well as the type locality, the BlancoLF in Texas (Dalquest, 1975). A small andapparently undescribed species of Hemiauch-enia, mostly represented by isolated postcra-nial elements, is found in New Mexico fau-nas ranging in age from early to late Blancan.Based on its stratigraphic position, the smallHemiauchenia metacarpal from Isleta isprobably either medial or late Blancan inage.

LOS LUNAS: The Los Lunas site (fig. 12.1,site 11) is located in strata of the Arroyo Oji-to Formation that underlie the Los Lunasvolcano, about 7 km west of Los Lunas inValencia County (Tedford, 1981). A mandi-ble of the giant marmot Paenemarmota, a ge-nus found in Hemphillian and Blancan fau-nas in western North America (Kurten andAnderson, 1980; Zakrzewski, 1998), wascollected at this site. The large size of theLos Lunas mandible suggests referral to P.barbouri, a species that occurs from the earlythrough the late Blancan (Morgan and Lucas,2000a). A K/Ar date of 1.1–1.3 Ma on theandesite of the Los Lunas volcano (Bachmanand Mehnert, 1978), which overlies the stratathat yielded the Paenemarmota jaw, providesa minimum age for the Los Lunas site (Ted-ford, 1981).

Several postcranial bones of a large camelwere collected from the Arroyo Ojito For-mation a few kilometers northwest of the Pa-enemarmota site, about 1 km north of NewMexico Route 6 (NMMNH Site L-3738;Morgan and Lucas, 2000a). These speci-mens, including a partial distal radio-ulnaand a magnum, probably represent a largeCamelops. A large undescribed species ofCamelops occurs in several medial and lateBlancan faunas elsewhere in New Mexico(Vanderhill, 1986; Morgan et al., 1998).

BELEN: Beginning south of the Los Lunasvolcano and extending south of Belen intonorthern Socorro County, badlands repre-senting the Arroyo Ojito Formation of Con-nell et al. (1999) are well exposed in an east-

facing escarpment just west of InterstateHighway 25 and several kilometers west ofthe Rio Grande. The NMMNH has two col-lections of Blancan vertebrates from south-west of Belen in Valencia County (fig. 12.1,site 12). In 1992, Bill Wood collected ver-tebrate fossils about 5 km southwest of Belen(NMMNH Site L-3778). Fossils from thissite include lower jaws of the gomphotheriidproboscidean Stegomastodon mirificus andpostcranial elements of Equus. ChristopherWhittle and several students collected fossilsfrom conglomeratic sandstone and slightlyindurated sandstone about 2 km southwest ofBelen (NMMNH Site L-3737), about 4 kmnorth of site L-3778. Fossils from this siteinclude a snake, the mole Scalopus, Geomys,Equus, and a small antilocaprid. Because ofthe close proximity of sites L-3737 and 3778southwest of Belen and their occurrence insimilar strata referred to the Arroyo OjitoFormation, the fossils from these two sitesare combined as the Belen Fauna (Morganand Lucas, 2000a).

The Belen Fauna (Morgan and Lucas,2000a) is composed of five species of mam-mals, including Scalopus (Hesperoscalops)cf. S. blancoensis, Geomys (Neterogeomys)cf. G. paenebursarius, Equus cf. E. caloba-tus, a small antilocaprid, and Stegomastodonmirificus. A dentary with m1–m3 from theBelen Fauna is the first mole (family Talpi-dae) ever reported from New Mexico, recentor fossil (Morgan and Lucas, 1999, 2000a).This mole is referred to Scalopus (Hesperos-calops), an extinct subgenus of Scalopus re-stricted to the Blancan. Three species of S.(Hesperoscalops) have been described, S. se-wardensis from the very early Blancan SawRock Canyon LF in Kansas, S. rexroadi fromthe early Blancan Rexroad and Fox Canyonfaunas in Kansas and the medial BlancanBeck Ranch LF in Texas, and S. blancoensisfrom the late Blancan Blanco LF in Texas(Hibbard, 1953; Dalquest, 1975, 1978; Kur-ten and Anderson, 1980). The Belen dentaryis tentatively referred to S. blancoensis basedon its similarity to that species in size andmorphological features. A dentary with acomplete dentition from Belen is identifiedas the extinct pocket gopher subgenus Geo-mys (Nerterogeomys). The morphology andsize of this mandible are similar to the spe-


cies G. (N.) paenebursarius, also identifiedfrom the Pajarito LF, and first described fromthe late Blancan Hudspeth and Red LightLFs of southwestern Texas (Strain, 1966;Akersten, 1972).

The most common fossils in the BelenFauna are postcranial elements of horses ofthe genus Equus, most of which are not di-agnostic at the species level. A nearly com-plete metatarsal is tentatively referred to thelarge, stilt-legged horse, E. calobatus, a spe-cies known from the late Blancan Santo Do-mingo LF (Tedford, 1981) and from lateBlancan and early Irvingtonian faunas in theMesilla basin (Vanderhill, 1986). A well-pre-served pair of mandibles with right and leftm2–m3 is referred to the gomphothere Ste-gomastodon mirificus. The presence of sevenlophids on m3 separates this specimen fromRhynchotherium and Cuvieronius, and thehighly complicated enamel with double tre-foiling distinguishes the teeth from the moreprimitive species S. rexroadensis.

Four mammals in the Belen Fauna are agediagnostic. The extinct subgenus Scalopus(Hesperoscalops) is restricted to the Blancanand the species S. blancoensis occurs in thelate Blancan. Geomys (Nerterogeomys) pa-enebursarius is known from two late Blan-can faunas in southwestern Texas (Strain,1966; Akersten, 1972), and the medial Blan-can Pajarito LF in the northern Albuquerquebasin (Tedford, 1981; Morgan and Lucas,2000a). Stegomastodon mirificus is knownfrom the medial Blancan through the earlyIrvingtonian, and Equus calobatus occurs inthe late Blancan and Irvingtonian (Kurtenand Anderson, 1980). The age of the BelenFauna is either medial or late Blancan. S.blancoensis and E. calobatus occur in lateBlancan faunas, but are not known from themedial Blancan, whereas G. (N.) paenebur-sarius and S. mirificus first appear in the me-dial Blancan. The lack of South Americanimmigrants in the Belen Fauna suggests amedial Blancan age, although their absencecould be related to biogeographic factors.Neotropical mammals are unknown fromBlancan faunas in northern New Mexico;however, Glyptotherium occurs in two earlyIrvingtonian faunas in the Albuquerque ba-sin, Tijeras Arroyo and Western Mobile. Wetentatively place the Belen Fauna in the me-

dial Blancan (fig. 12.2) based on similaritieswith other medial Blancan faunas (e.g., Pa-jarito) from the Arroyo Ojito Formation inthe Albuquerque basin.

MESAS MOJINAS: An astragalus of a smallcamelid (NMMNH 29936) was collected byRichard Lozinsky in 1986 from the ArroyoOjito Formation, southeast of Mesas Mojinasin the Gabaldon badlands west of Belen inValencia County (NMMNH Site L-4253; fig.12.1, site 13). In their review of the earlyHemphillian (late Miocene) Gabaldon Faunafrom the Popotosa Formation, which under-lies the Arroyo Ojito Formation, Lozinskyand Tedford (1991) referred this specimen toHemiauchenia sp. and noted that it was theonly fossil recovered from post-Hemphillianstrata in the Gabaldon badlands. The Gabal-don specimen is very similar to two astragaliof a small Hemiauchenia from the earlyBlancan Buckhorn LF in southwestern NewMexico (Morgan et al., 1997). This smallspecies of Hemiauchenia is known from sev-eral other Blancan faunas in New Mexico.

VEGUITA: A site in the Arroyo Ojito For-mation about 1 km east of the Rio Puercoand 10 km northwest of Veguita in northern-most Socorro County (NMMNH Site L-2941; fig. 12.1, site 14) in the southern Al-buquerque basin has produced a partial max-illa with left P2–M3 of the large horse Equusscotti (Morgan and Lucas, 2000a). Theseteeth are characterized by their large size,fairly complicated enamel pattern of the fos-settes, elongated protocone with a lingual in-dentation, and presence of a pli caballin. E.scotti is the common large horse in NewMexico faunas ranging in age from medialBlancan through early Irvingtonian. A Blan-can age is more likely considering that mostsites from the Arroyo Ojito Formation in thesouthern portion of the Albuquerque basinproduce Blancan mammals.

SEVILLETA: Denny (1940) found Blancanfossils in sands and gravels, probably derivedfrom the Arroyo Ojito Formation, frombluffs west of the Rio Grande and just northof the Rio Salado in the southernmost por-tion of the Albuquerque basin in northernSocorro County (fig. 12.1, site 15). This siteis located on land now included within theSevilleta National Wildlife Refuge. The fau-na reported by Denny consists of the gom-


Fig

.12

.2.

Cor

rela

tion

char

tsh

owin

gth

ere

lati

veag

esof

late

Hem

phil

lian

,B

lanc

an,

and

Irvi

ngto

nian

vert

ebra

tefa

unas

from

the

nort

hern

and

cent

ral

Rio

Gra

nde

Val

ley

inN

ewM

exic

o,in

clud

ing

the

San

Lui

s,E

span

ola,

Alb

uque

rque

,S

ocor

ro,

Eng

le,

and

Pal

omas

basi

ns.T

hech

rono

logi

cal

lim

its

ofth

em

amm

alia

nfa

unas

are

indi

cate

dby

the

vert

ical

heig

htof

the

boxe

sen

clos

ing

the

faun

aor

site

nam

es.

The

lith

ostr

atig

raph

icun

itfr

omw

hich

each

faun

aor

site

was

deri

ved

isal

soin

dica

ted

wit

hin

the

box.

Mag

neto

chro

nolo

gyis

from

Ber

ggre

net

al.

(199

5).

Thr

eesy

stem

sfo

rsu

bdiv

idin

gth

eB

lanc

anN

AL

MA

are

indi

cate

dto

the

left

(Ted

ford

,19

81;

Rep

enni

ng,

1987

;W

oodb

urne

and

Sw

ishe

r,19

95).


phothere Stegomastodon mirificus and atooth of Equus. We have not been able torelocate Denny’s fossils, and thus the iden-tifications are taken from his paper and mustbe considered tentative. We recently collect-ed fossils from outcrops of the Arroyo OjitoFormation in this same general area, north ofthe Rio Salado on the La Joya Game Refuge.We found teeth and postcranial elements rep-resenting two species of Equus, E. simplici-dens and a larger horse, tentatively identifiedas E. scotti. The Sevilleta fauna is similar tothe medial Blancan Arroyo de la Parida LF,derived from the Palomas Formation about15 km farther south in the northern Socorrobasin.

SOCORRO BASIN

ARROYO DE LA PARIDA: Vertebrate fossilswere first found in Arroyo de la Parida in1935, about 6 km northeast of Socorro, So-corro County (fig. 12.1, site 16). Needham(1936) reported a complete pair of lowerjaws of the gomphotheriid proboscideanRhynchotherium and a lower molar of thehorse Plesippus (now considered a subgenusof Equus) from an exposure of sands andgravels of the Santa Fe Group on the southside of Arroyo de la Parida, about 2 km eastof its confluence with the Rio Grande. Ad-ditional vertebrate fossils were collectedfrom this same exposure by students from theNew Mexico Institute of Mining and Tech-nology (DeBrine et al., 1963). Curt Teichert,a well-known German invertebrate paleon-tologist, collected a sample of vertebrate fos-sils from the vicinity of Arroyo de la Paridain 1953, and donated these fossils to theAmerican Museum of Natural History. Theonly locality information associated withTeichert’s sample was that the fossils werecollected ‘‘about four miles north of Socorro,New Mexico.’’ Based on the general locality,preservation of the fossils, and the compo-sition of the fauna, there is little doubt thatTeichert’s fossils are from the area that yieldsthe Arroyo de la Parida LF. The fossils col-lected by Teichert were summarized by Ted-ford (1981), and include three species ofhorses, Equus simplicidens, E. cf. E. cum-minsii, and E. cf. E. scotti, the small antilo-caprid Capromeryx, and the gomphothere

Stegomastodon. Lucas and Morgan (1996)described and illustrated the mandibles ofRhynchotherium first mentioned by Need-ham, and referred them to the species R. fal-coneri, originally described from the BlancoLF in Texas. Lucas and Morgan (1996) alsosummarized the biostratigraphy of the Ar-royo de la Parida LF, including fossils col-lected in 1996 by two students from NewMexico Tech, Ed Frye and Mike O’Keeffe.We visited the Arroyo de la Parida area sev-eral times during 2000 and collected numer-ous additional fossils from 15 different sites(Morgan et al., 2000).

The Arroyo de la Parida LF is derivedfrom a 70-m sequence of sands and gravelsthat constitute the axial river (ancestral RioGrande) facies of the Palomas Formation.The strata in the vicinity of Arroyo de la Par-ida are located at the northern end of the So-corro basin, representing one of the northern-most occurrences of the Palomas Formation,which has its type area about 100 km farthersouth in Palomas Creek near Truth or Con-sequences in Sierra County (Lozinsky,1986). The Arroyo de la Parida LF is com-posed of 10 vertebrates: the land tortoiseHesperotestudo; the ground sloth Megalonyxcf. M. leptostomus; three horses, Equus cf. E.cumminsii, E. scotti, and E. simplicidens; twocamelids, a large Camelops and a smallHemiauchenia; the small antilocaprid Cap-romeryx; and two proboscideans, Rhyncho-therium falconeri and Stegomastodon sp.This is a fairly typical faunal assemblagefound in New Mexico Blancan sites, mostlyconsisting of large grazing ungulates anddominated by horses of the genus Equus.

Five mammals from the Arroyo de la Par-ida LF are restricted to the Blancan, includ-ing Megalonyx leptostomus, Equus cummin-sii, E. simplicidens, the large Camelops, andRhynchotherium falconeri. The most age-di-agnostic of these taxa is Rhynchotherium, agomphothere that became extinct in the latePliocene at about 2.2 Ma together with sev-eral other characteristic genera of Blancanmammals. The lower jaws of R. falconerifrom Arroyo de la Parida were collected nearthe top of the local section of the PalomasFormation, suggesting that the entire fauna,most of which occurs some 40 m lower inthe section, is older than 2.2 Ma. An early


Blancan age for the Arroyo de la Parida LFcan be ruled out by the presence of E. scottiand Camelops, both of which first appear inNew Mexico faunas during the medial Blan-can. The absence of South American immi-grants suggests an age greater than 2.7 Ma.Megalonyx is the only Blancan mammal ofSouth American origin that was not a partic-ipant in the Great American Interchange. Me-galonyx or its progenitor arrived from SouthAmerica in the late Miocene about 9 Ma. M.leptostomus is fairly widespread in earlythrough late Blancan faunas. The Arroyo dela Parida LF is interpreted to be medial Blan-can in age (3.6–2.7 Ma), and is similar to theCuchillo Negro Creek LF from the PalomasFormation in the Engle Basin near Truth orConsequences.

FITE RANCH: Tedford (1981) reported post-cranial bones of Equus and Camelops col-lected by George Pearce in 1953 from pum-ice-bearing sands on the Dean Fite Ranchnear San Antonio in the Socorro basin, So-corro County (fig. 12.1, site 17). Specimensin the F:AM collections from Fite Ranchconsist of an astragalus of Equus and a par-tial metatarsal of Camelops. Needham (1936)reported a partial humerus, radius, and ulnaof the turkey Meleagris, apparently from thissame locality (Tedford, 1981). Needham (p.537) described this locality as ‘‘a bed ofpumicite . . . about three and one half milesnortheast of San Antonio, Socorro County,along the east bluff of the Rio Grande. It [thebed of pumicite] is underlain by some thirtyfeet of light-colored gravel and sand and buffsilt, typical of the Santa Fe formation as de-veloped east of the Rio Grande near Socor-ro’’ (i.e., Arroyo de la Parida). Tedford notedthat the pumice-bearing sands on the FiteRanch were attributed to the Bandelier erup-tions, indicating an age of 1.6–1.2 Ma (Izettet al., 1981; Izett and Obradovich, 1994).This would suggest an early Irvingtonianage, although the fossil vertebrates from FiteRanch are not age diagnostic.

SAN MARCIAL BASIN

SILVER CANYON: Gary Morgan, MikeO’Neill, and Brenda Wilkinson collected asmall sample of fossils in 1998 from the Pal-omas Formation near Silver Canyon in the

San Marcial basin at the very northern endof Elephant Butte Lake in southern SocorroCounty (NMMNH site L-3682; fig. 12.1, site18). The Silver Canyon site consists of threetaxa of mammals, a rodent tentatively iden-tified as the wood rat Neotoma, the horse Eq-uus, and an indeterminate gomphothere. Themost common fossils are proboscidean toothand tusk fragments and postcranials, identi-fiable only as Gomphotheriidae. Equus isrepresented in the fauna by postcranial re-mains. A mandible of a fairly large rodentappears to be referable to Neotoma, althoughthe teeth are too worn for a species-levelidentification. The age of this fauna cannotbe determined on the basis of the fossil ma-terial currently known, although a Blancanage is most likely considering that all othervertebrate faunas so far known from the Pal-omas Formation are Blancan.

ENGLE BASIN

ELEPHANT BUTTE LAKE: Joseph Rak andCharles Falkenbach of the Frick Laboratorycollected fossil vertebrates in the late 1920sfrom axial river gravels of the ancestral RioGrande in the Engle and Palomas basins inthe vicinity of Hot Springs (now called Truthor Consequences) in Sierra County. Fossilsfrom the Engle basin on the western side ofElephant Butte Lake north of Truth or Con-sequences are called the Elephant Butte LakeFauna (fig. 12.1, site 19). Tedford (1981) at-tributed these strata to the Sierra LadronesFormation, but they have since been referredto the Palomas Formation (Lozinsky, 1986).The precise localities and stratigraphy ofthese fossils are not known; however, theywere certainly derived from the Palomas For-mation, and are similar in age to the nearbyCuchillo Negro Creek LF (see below). Mam-mals identified by Tedford from ElephantButte Lake are the horse Equus simplicidens,the tapir Tapirus, and the giant camel Gi-gantocamelus. Since 1981, additional fossilsreferable to the Elephant Butte Lake Faunahave been collected in the vicinity of RockCanyon on the western shore of ElephantButte Lake about 5 km north of Truth orConsequences, and include the giant tortoiseHesperotestudo, a mandible of Gigantoca-melus cf. G. spatula, and a skull of the gom-


phothere Stegomastodon cf. S. rexroadensis.E. simplicidens and Gigantocamelus are in-dicative of the Blancan, and S. rexroadensissuggests an early or medial Blancan age.Tedford considered these sites to be medialBlancan because of their close stratigraphicassociation with a basalt flow dated at 2.9 60.3 Ma from Mitchell Point on the westernside of Elephant Butte Lake (Bachman andMehnert, 1978).

CUCHILLO NEGRO CREEK: Vertebrate fossilsfrom the Palomas Formation north of Cuch-illo Negro Creek in the Engle Basin in SierraCounty (fig. 12.1, site 20) were named theCuchillo Negro Creek LF by Lucas and Oak-es (1986). Fossils were collected from theCuchillo Negro Creek area in 1983 and 1984by University of New Mexico field crewsand in 1998 and 1999 by NMMNH fieldcrews. Lozinsky (1986) recognized two in-formal members of the Palomas Formationin this area, the axial facies consisting ofabout 30 m of sand with lenses of gravel andclay and the piedmont facies consisting ofabout 50 m of sandy silt and conglomerate.Most of the fossils were derived from theaxial facies, which was deposited by an an-cestral Rio Grande. A basalt flow dated at2.9 Ma from Mitchell Point, about 15 kmnorth of the Cuchillo Negro Creek sites, in-terfingers with the axial facies of the PalomasFormation (Lozinsky, 1986).

The Cuchillo Negro Creek LF is com-posed of 10 species (Lucas and Oakes, 1986;this report): 3 turtles, including a small landtortoise of the genus Hesperotestudo, themud turtle Kinosternon, and an aquatic mem-ber of the family Emydidae, and 7 mammals,including the borophagine canid Borophagushilli, the procyonid Bassariscus sp., the equidEquus cf. E. simplicidens, the camelids Ca-melops sp., Hemiauchenia blancoensis, andHemiauchenia small sp., and the gompho-theriid proboscidean Stegomastodon re-xroadensis.

A nearly complete dentary with i2–3, c,and p2–m2 identified as Borophagus diver-sidens by Lucas and Oakes (1986) was re-ferred to B. hilli by Wang et al. (1999). Al-though most Borophagus fossils from theearly Blancan were referred to B. diversidensby previous authors, these specimens aremore similar in size and morphology to the

late Hemphillian and early Blancan speciesB. hilli. The larger and more highly derivedspecies B. diversidens appears in the late ear-ly Blancan and survives until the late Blan-can (Wang et al., 1999). An edentulous man-dible from Cuchillo Negro Creek representsthe first New Mexico Pliocene record of theringtail Bassariscus. The only Blancan spe-cies of Bassariscus, B. casei from the earlyBlancan Rexroad Fauna in Kansas, is distin-guished from the extant B. astutus on the ba-sis of dental characters that cannot be ob-served in the Cuchillo Negro Creek jaw.

Lucas and Oakes (1986) identified the pal-ate of a horse from the Cuchillo Negro CreekLF as Equus simplicidens. Two associatedupper molars found in 1998 match the orig-inal dental sample. Although these teeth haveseveral features that differ somewhat fromtypical E. simplicidens (e.g., fairly compli-cated fossettes and slight lingual indentationof the protocone), this species is the onlyBlancan Equus that is similar in morphologyand size to the teeth from Cuchillo NegroCreek. There are three taxa of camelids fromCuchillo Negro Creek. The typical largeBlancan llama Hemiauchenia blancoensiswas reported previously (Lucas and Oakes,1986). A small species of Hemiauchenia isknown from an adult distal tibia. This ap-parently undescribed species of llama occursin six Blancan faunas in New Mexico. Alarge undescribed species of Camelops, rep-resented by a large proximal phalanx fromCuchillo Negro Creek, occurs in several oth-er Blancan faunas in New Mexico (Morganet al., 1998).

A proboscidean is represented at CuchilloNegro Creek by a pair of mandibles withheavily worn m3s (Lucas and Oakes, 1986)and by a recently collected partial m3 in me-dium wear. The mandibles have a short,straight symphysis lacking tusks. The m3s ofthese two specimens are similar in size anddental features, including the presence of sixlophids and a simple trefoil pattern. Thecombination of six lophids on the m3 and theabsence of lower tusks excludes all otherBlancan genera of proboscideans except Ste-gomastodon. The smaller number of lophidson m3 and simple trefoiling distinguish theCuchillo Negro Creek teeth from the moreadvanced species S. mirificus, and suggest re-


ferral to the early to medial Blancan S. rex-roadensis.

Lucas and Oakes (1986) proposed a me-dial Blancan age (about 3.0 Ma) for theCuchillo Negro Creek LF, based on biostra-tigraphy and correlation with the 2.9 MaMitchell Point basalt. They suggested thatthe Cuchillo Negro Creek LF is similar to theRexroad Fauna in Kansas and the BensonFauna in Arizona. The presence of Came-lops, a genus that supposedly did not appearuntil after 3.7 Ma (Lindsay et al., 1984), isindicative of a medial Blancan age, and Ste-gomastodon rexroadensis occurs in both ear-ly and medial Blancan faunas. The absenceof South American immigrant mammals in-dicates a pre-late Blancan age (older than 2.7Ma). The presence of Borophagus hilli sug-gests an early Blancan age according toWang et al. (1999), although this same spe-cies occurs in the medial Blancan HagermanFauna in Idaho. A more precise age deter-mination for the Cuchillo Negro Creek LFmust await the discovery of additional age-diagnostic taxa, or other data such as mag-netostratigraphy. In the near future, we in-tend to determine the relative stratigraphicposition of this fauna compared to the betterknown early Blancan Truth or ConsequencesLF, located about 5 km farther south.

PALOMAS BASIN

TRUTH OR CONSEQUENCES: The Truth orConsequences LF is derived from fine-grained sediments of the Palomas Formationin a roadcut on Interstate 25 about 2 kmsouth of Truth or Consequences in SierraCounty (Repenning and May, 1986; fig. 12.1,site 21). The site was discovered by ArthurHarris of the University of Texas at El Pasoand then worked in the early 1980s byCharles Repenning and Steven May of theU.S. Geological Survey in Denver. GaryMorgan, Paul Sealey, and Spencer Lucas be-gan work at this site in 1997 and have addednumerous taxa to the fauna, including bothlarge and small species (table 12.1). Repen-ning and May recovered most of their fossilsby excavation, whereas the more recentNMMNH collections have been obtained pri-marily through screenwashing.

The stratigraphic section that includes the

Truth or Consequences LF is composed ofabout 20 m of poorly consolidated sand andpebbly sand, with two interbedded mudstonelayers, referred to the Palomas Formation.Most of the vertebrate fossils occur in green-ish to reddish mudstones in the lower thirdof the roadcut. The preservation of fossils inthese mudstones is excellent, and includesnumerous mandibles, maxillae, and partialskulls of both small and large mammals. Werecently recovered fossils of aquatic species,including a duck and two partial shells ofemydid turtles, in fine sand at the base of thelocal section. Fine-grained units are uncom-mon and discontinuous within the axial riverfacies of the Palomas Formation, which isdominated by sands and gravels.

The Truth or Consequences LF, as origi-nally described by Repenning and May(1986), consisted of 13 species: 4 reptiles,including the mud turtle Kinosternon, thebox turtle Terrapene, the fence lizard Sce-loporus, and the coachwhip snake Mastico-phis; and 9 mammals, including the rabbitsHypolagus vetus and Notolagus lepusculus,the pocket gopher Geomys (Nerterogeomys)minor, the cotton rat Sigmodon, the rice ratcf. Oryzomys, the wood rat Neotoma quad-riplicata, the horse Equus (Plesippus), thedeer Odocoileus brachyodontus, and thegomphothere Stegomastodon. Recent addi-tions to the fauna include an aquatic emydidturtle, another snake, a duck and a galliformbird, and six mammals—a shrew, the moleScalopus, a small sciurid, the large canidBorophagus cf. B. hilli, the peccary Platy-gonus cf. P. bicalcaratus, and the small an-tilocaprid Capromeryx. The Truth or Conse-quences LF is now composed of 23 species,including 15 mammals (table 12.1), makingit one of the most diverse Blancan vertebratefaunas from New Mexico.

Many of the mammals from the Truth orConsequences LF are age diagnostic, severalof which suggest an early Blancan age. Re-penning and May (1986) referred the smallrabbit to Notolagus lepusculus, a speciesnamed by Hibbard (1939) from the late earlyBlancan Rexroad 3 Fauna of Kansas (Blan-can II of Repenning, 1987). The larger rabbitwas identified as Hypolagus vetus, a speciesknown from the Hemphillian through themedial Blancan (White, 1987). The pocket


gopher was referred to the small speciesGeomys (Nerterogeomys) minor, describedfrom Rexroad 3 (Hibbard, 1950, 1967). Theprimitive wood rat Neotoma (Paraneotoma)quadriplicata is intermediate in size betweenthe oldest species of pack rat, N. (P.) saw-rockensis from the very early Blancan SawRock Canyon LF in Kansas, and N. (P.)quadriplicata from Rexroad 3 (Hibbard,1941, 1967). Repenning and May (1986) ten-tatively referred a small sigmodontine rodentto the extant genus Oryzomys. Czaplewski(1987) noted that the Oryzomys from Truthor Consequences was similar to his new ge-nus Jacobsomys from the early Blancan(about 4 Ma) Verde LF in Arizona, but wassmaller than the Verde species J. verdensis.The Sigmodon from Truth or Consequences,referred here to S. medius, may represent oneof the earliest records of this genus. Cza-plewski (1987) also recorded S. medius fromthe Verde LF.

The Truth or Consequences LF consistsprimarily of microvertebrates. Because of therarity of large mammals, it is difficult tomake biostratigraphic comparisons with oth-er New Mexico Blancan faunas, most ofwhich are composed of large vertebrates. Thecervid Odocoileus brachyodontus, identifiedfrom Truth or Consequences by a maxillaryfragment and antler, was first described fromthe early Blancan Fox Canyon Fauna of Kan-sas (Oelrich, 1953). Odocoileus appears inthe early Blancan as an immigrant from theOld World. It is one of the genera whose firstappearance helps to define the beginning ofthe Blancan (e.g., Woodburne and Swisher,1995). The rostrum of a large peccary is sim-ilar to the large species Platygonus bicalcar-atus. Although the genus Platygonus sup-posedly appeared at the beginning of the me-dial Blancan at about 3.6 Ma (Lindsay et al.,1984), an occurrence in the early Blancanwould not be surprising. A p2 of Borophagusis similar in size and morphology to the p2of B. hilli from Cuchillo Negro Creek, a spe-cies known elsewhere from the late Hem-phillian and early Blancan (Wang et al.,1999). Fossils of Equus (Plesippus), Cap-romeryx, and Stegomastodon are too incom-plete for further identification. Nannippusand camelids are both absent from the Truthor Consequences LF.

Repenning and May (1986) suggested anearly Blancan age (between 4.2 and 4.0 Ma,early Blancan II of Repenning, 1987) for theTruth or Consequences LF based on bothbiostratigraphy and magnetostratigraphy. Re-penning and May (1986) correlated the Truthor Consequences magnetostratigraphic sec-tion of 11 normally magnetized samplesfrom three levels to the Nunivak Subchronof the Gilbert Chron, primarily on the basisof the similarity of its fauna with other fau-nas from the Nunivak or the next oldest nor-mal subchron in the Gilbert (Sidufjall), anda more primitive aspect than faunas (e.g.,Rexroad 3) derived from the next youngestnormal subchron in the Gilbert (Cochiti).They gave an age range of 4.20–4.05 Ma forthe Nunivak, but the age of this subchron hassince been revised downward to 4.62–4.48Ma (Berggren et al., 1995). The correlationof the Truth or Consequences magnetostrati-graphic section to the Nunivak Subchronshould be considered tentative since it wasbased on a few samples through a limitedstratigraphic section (Mack et al., 1993). Weintend to measure a longer stratigraphic sec-tion of the Palomas Formation through theTruth or Consequences LF, in hopes of de-termining the stratigraphic position of thisfauna relative to three other nearby Blancanfaunas from the Palomas Formation, Cuchi-llo Negro Creek and Elephant Butte Lake tothe north and Palomas Creek to the south.We anticipate that a more detailed magneto-stratigraphic section eventually will be takenthrough this section.

PALOMAS CREEK: Joseph Rak and CharlesFalkenbach collected fossil vertebrates in1927 and 1928 from exposures of the distalpiedmont facies of the Palomas Formationsouthwest of Hot Springs (5 Truth or Con-sequences) in Palomas Creek, Sierra County(Tedford, 1981; fig. 12.1, site 22). PalomasCreek is the type area of the Palomas gravel,now called the Palomas Formation (Lozin-sky, 1986). The Palomas Creek LF is in thePalomas basin about 8–10 km southwest ofthe Truth or Consequences LF. PalomasCreek has a fairly diverse Blancan faunacomposed of nine species (table 12.1, afterTedford, 1981): the tortoise Hesperotestudoand eight mammals, including the pocket go-pher Geomys (Geomys); the cotton rat Sig-


modon medius; the horses Nannippus pen-insulatus, Equus simplicidens, and E. cf. E.cumminsii; a peccary; a large Camelops; andthe mastodont Mammut raki. Nannippus, E.simplicidens, E. cumminsii, and the large Ca-melops are characteristic of New MexicoBlancan faunas. The absence of South Amer-ican immigrants suggests a pre-late Blancanage. The type mandible of Mammut (5 Mas-todon) raki (Frick, 1933) from PalomasCreek is one of the few known BlancanMammut, and the only one referred to a spe-cies other than M. americanum, the typicalPleistocene mastodon (Lucas and Morgan,1999).

Magnetostratigraphy and radioisotopicdates provide additional geochronologic datapertaining to the age of Palomas Formationin the Palomas basin (Mack et al., 1993,1998). K/Ar dates on basalts in the Palomasbasin include a flow dated at 4.5 6 0.1 Main the western part of the basin that is eitherbelow or within the lowermost Palomas For-mation and a flow dated at 3.1 6 0.1 Mainterbedded with alluvial fan conglomeratesof the Palomas Formation in the eastern partof the basin (Seager et al., 1984; Mack et al.,1998). A magnetostratigraphic section in thePalomas Formation from Palomas Creeksampled mostly reversely magnetized stratareferred to the Matuyama Chron, but includ-ed about 10 m of normally magnetized stratareferred to the Gauss Chron at the bottom ofthe section (Mack et al., 1993). The precisestratigraphic position of the Palomas Creekfossils is unknown, but the paleomagneticdata strongly suggest the fauna was derivedfrom low in the section. The combination ofmagnetostratigraphy and biostratigraphy in-dicates a medial Blancan (3.6–2.7 Ma) agefor the Palomas Creek LF.

HATCH-RINCON BASIN

HATCH: Blancan and early Irvingtonianfossils occur in the Camp Rice Formation insouthern New Mexico, from Hatch and Rin-con Arroyo in the Hatch-Rincon basin innorthern Dona Ana County south through theJornada and Mesilla basins and into Texas.Hawley (1978) mentioned the presence ofBlancan fossils from the vicinity of Hatch,but did not list any taxa. Paul Sealey and

NMMNH field crews collected vertebratefossils in 1990 and 1998 from the Camp RiceFormation about 5 km west of Hatch (fig.12.1, site 23). The Camp Rice Formation isunconformably underlain by Miocene redbeds of the Rincon Valley Formation in thevicinity of Hatch. This is similar to a strati-graphic section about 30 km southeast ofHatch in the Jornada basin near TonucoMountain, where the Tonuco Mountain LFwas collected (Morgan et al., 1998). Theonly fossil previously reported from Hatch isa partial skeleton of the long-nosed snakeRhinocheilus (Lucas et al., 1995).

On the basis of fossils in the NMMNHcollection, the Hatch LF is composed of 12species: the land tortoises Gopherus andHesperotestudo, the mud turtle Kinosternon,Rhinocheilus, and eight species of mammals(table 12.1) including two unidentified rab-bits, the pocket gopher Geomys (Nerterogeo-mys) cf. G. (N.) paenebursarius, the badgerTaxidea, a small cat probably of the genusLynx, the horse Equus, the camelid Hem-iauchenia cf. H. blancoensis, and the smallantilocaprid Capromeryx. Land tortoises arethe most abundant members of the Hatchfauna. Specimens of mammals are less com-mon, particularly ungulates. Equus is repre-sented by fragmentary teeth, Hemiaucheniaby postcranial remains, and Capromeryx bya single tooth. Two leporids are present basedon two distal femora of very different size.Taxidea is identified from a distal radius.Badgers are known from two other NewMexico Blancan faunas, Buckhorn and Ton-uco Mountain (Morgan et al., 1997, 1998).The small cat is represented by a maxillaryfragment with a partial P4 (NMMNH 25308)that compares well in size and other featuresto Lynx rexroadensis, known from late Hem-phillian and Blancan faunas (MacFadden andGaliano, 1981). Two pocket gopher mandi-bles (NMMNH 25324, 25329) from Hatchare similar to mandibles referred to Geomys(Nerterogeomys) paenebursarius from theBelen and Pajarito Faunas in the Albuquer-que basin (Morgan and Lucas, 2000a).

The age of the Hatch LF is somewhat un-certain because most of the mammalian taxaare not identifiable below the generic level.A medial Blancan age is suggested by thefaunal and stratigraphic similarity to the


nearby Tonuco Mountain LF (Morgan et al.,1998). A pre-late Blancan age is indicated bythe lack of South American immigrant mam-mals that appeared in faunas after 2.7 Ma. Amagnetostratigraphic section in the CampRice Formation at Hatch Siphon, located sev-eral kilometers west of the badlands that pro-duced the Hatch LF, samples essentially theentire Gauss Chron, including both the Ka-ena and Mammoth Subchrons (Mack et al.,1993). The lowermost part of the sectiondoes not cross the Gilbert/Gauss boundaryand is thus younger than 3.6 Ma, whereas theupper 10 m samples the Matuyama Chron.The Hatch Siphon section is similar to themagnetostratigraphic section for Cedar Hillthat contains the medial Blancan TonucoMountain LF (Mack et al., 1993; Morgan etal., 1998; see below), further supporting amedial Blancan age for the Hatch LF.

RINCON ARROYO: Several fragmentaryteeth and partial metapodials of Equus werecollected from the Camp Rice Formation inRincon Arroyo by Paul Knight and PaulSealey. Rincon Arroyo is in the Hatch-Rin-con basin in northern Dona Ana Countyabout 10 km east of Hatch (fig. 12.1, site 24).The most significant aspect of Rincon Ar-royo is the detailed geochonologic data avail-able for the stratigraphic section, includingmagnetostratigraphy (Mack et al., 1993) anda dated pumice-clast conglomerate (Mack etal., 1998). The lower half (about 50 m) ofthe Rincon Arroyo section is in the GaussChron and the upper portion (also about 50m) is in the Matuyama Chron, and includesthe Reunion, Olduvai, and Jaramillo sub-chrons (Mack et al., 1993). Between the Ol-duvai and Jaramillo subchrons in the upperpart of the section is a pumice-clast conglom-erate dated at 1.60 Ma, which correlates withthe lower Bandelier eruption (Mack et al.,1998). The Rincon Arroyo section crossesthe Blancan/Irvingtonian boundary at the topof the Olduvai Subchron in the upper thirdof the section. Unfortunately, Rincon Arroyois not particularly fossiliferous, and the fewfossils recovered so far are not age diagnos-tic. Future field work in Rincon Arroyohopefully will yield additional mammal fos-sils from this well-dated section.

JORNADA BASIN

TONUCO MOUNTAIN: The Tonuco MountainLF is a medial Blancan vertebrate assem-blage from the Cedar Hill area southeast ofTonuco Mountain (also called San DiegoMountain) in northern Dona Ana County,southern New Mexico (Morgan et al., 1998;fig. 12.1, site 25). The fossils are derivedfrom the axial river facies of the Camp RiceFormation in the western Jornada Basin. Thestratigraphic section of the Camp Rice For-mation at Cedar Hill consists of about 50 mof sandstone and conglomerate, with a minorcomponent of sandy mudstone, and is un-conformably underlain by Miocene red bedsof the Rincon Valley Formation (Morgan etal., 1998).

The Tonuco Mountain LF is composed of16 species: the mud turtle Kinosternon, theland tortoises Gopherus and Hesperotestudo,a duck, and 12 mammals including an inde-terminate rabbit; the badger Taxidea; thecoyote-like canid Canis lepophagus; the bor-ophagine canid Borophagus sp.; the horsesNannippus peninsulatus, Equus simplicidens,and E. scotti; the peccary Platygonus cf. P.bicalcaratus; the camelids Camelops, Hem-iauchenia blancoensis, and a small Hem-iauchenia; and the gomphothere Cuvieron-ius. Among these taxa, Borophagus, C. le-pophagus, N. peninsulatus, E. simplicidens,P. bicalcaratus, and H. blancoensis are in-dicative of the Blancan, and several of thesetaxa help to further limit the age of this faunawithin the Blancan. E. simplicidens is absentfrom very early Blancan faunas, Platygonusand Camelops supposedly do not appear untilthe beginning of the medial Blancan (Lind-say et al., 1984), and most Blancan recordsof Nannippus in the southwestern UnitedStates predate the Gauss/Matuyama magneticreversal at 2.6 Ma. The absence of SouthAmerican immigrants suggests the fauna isolder than 2.7 Ma, the earliest date for theonset of the Great American Interchange.The biostratigraphic data restrict the age ofthe Tonuco Mountain LF to the medial Blan-can (between 3.6 and 2.7 Ma). A magneto-stratigraphic study of the Camp Rice For-mation at Cedar Hill helps to further con-strain the age of this fauna (Mack et al.,1993). The entire Cedar Hill section is within


the Gauss Chron (younger than 3.6 Ma), andthe fossiliferous interval is below the top ofthe Kaena Subchron (older than 3.0 Ma). Thecombination of biostratigraphic and magne-tostratigraphic data limit the age of the Ton-uco Mountain LF to the medial Blancan, be-tween 3.6 and 3.0 Ma.

MESILLA BASIN

Two Blancan and two early Irvingtonianvertebrate faunas occur in the Camp RiceFormation in the Mesilla Basin, Dona AnaCounty, southern New Mexico (Tedford,1981; Vanderhill, 1986; Lucas et al., 1999,2000). In his doctoral dissertation, Vanderhill(1986) referred to these faunas as Faunule A(late Blancan), Faunule B (latest Blancan/earliest Irvingtonian), and Faunule C (earlyIrvingtonian) of the Mesilla basin, but didnot apply formal names to them. We followthe letter designations of Vanderhill (1986)for the faunas from the southern Mesilla ba-sin, from Chamberino south to the Mexicanborder near Santa Teresa; however, we usethe terms Mesilla Basin Fauna A, B, and C(shortened to Mesilla A, B, and C) to con-form to the nomenclature as discussed aboveunder Methods (i.e., the Mesilla basin ver-tebrate assemblages fit the definition of fau-nas, rather than faunules or local faunas).The three faunas from the southern Mesillabasin are stratigraphically superposed anddiffer in age, as documented by both biostra-tigraphy and magnetostratigraphy (Vander-hill, 1986), and thus should eventually be as-signed formal names to eliminate confusion.The Tortugas Mountain LF includes two ear-ly Irvingtonian sites in the northern Mesillabasin (Lucas et al., 1999, 2000) that wereincluded in Fauna (5 Faunule) C by Van-derhill (1986). Mesilla Basin Fauna C is hererestricted to the early Irvingtonian faunafrom the southern Mesilla basin.

Vertebrate fossils were first collected inthe southern Mesilla basin in 1929 by JosephRak of the Frick Laboratory. George Pearce,also of the Frick Laboratory, returned to thesouthern Mesilla basin in 1949 and accu-mulated a sizeable collection, including a gi-ant tortoise shell, several glyptodont shells,and a nearly complete tapir skeleton. Ted-ford’s (1981) summary of the Mesilla basin

fauna was based on the Frick fossils (F:AM)now housed in the AMNH. The largest col-lection of fossils from the Mesilla basin wasamassed from the 1950s through the 1980sby William Strain, Arthur Harris, and theirstudents at the University of Texas at El Paso(UTEP). The UTEP and F:AM collectionsformed the basis for the detailed review ofthe vertebrate paleontology, lithostratigraphy,and magnetostratigraphy of the Mesilla basinfaunas by Vanderhill (1986) in his doctoraldissertation. Beginning in 1999, field crewsfrom the NMMNH began collecting fossilsfrom the Camp Rice Formation in the vicin-ity of Chamberino and La Union in thesouthern Mesilla Basin, and discovered a mi-crovertebrate site near Chamberino in the lat-est Blancan portion of the Camp Rice For-mation. The discussion of the southern Mes-illa Basin faunas is primarily abstracted fromVanderhill’s (1986) unpublished dissertation,with additional data from recent field work.

TORTUGAS MOUNTAIN: Vertebrate fossilshave been known for 40 years from gravelpits in the northern Mesilla Basin (Ruhe,1962; Hawley et al., 1969). The TortugasMountain LF includes fossils collected fromtwo gravel pits near Tortugas Mountain, sev-eral kilometers east of Las Cruces in DonaAna County (Lucas et al., 1999, 2000; fig.12.1, site 26). These pits expose axial riversands and gravels of an ancestral Rio Grandein the upper part of the Camp Rice Forma-tion. A palate of Stegomastodon, two man-dibles of Cuvieronius, and isolated teeth ofMammuthus were collected from a gravel piton the northwestern side of Tortugas Moun-tain (NMMNH site L-3537). A palate of Cu-vieronius, a Mammuthus tooth, and severalteeth and postcranial elements of Equus werefound from about the same stratigraphic levelin the Inman Gravel Pit (NMMNH site L-3649), about 3 km north of Tortugas Moun-tain (Hawley et al., 1969; Tedford, 1981;Vanderhill, 1986; Lucas et al., 1999, 2000).

With the exception of several Equus fos-sils figured in Hawley et al. (1969) that wecannot locate, the Tortugas Mountain LFconsists of three species of proboscideans(Lucas et al., 1999, 2000), the gomphotheresCuvieronius tropicus and Stegomastodonmirificus and the mammoth Mammuthus im-perator. Tortugas Mountain is only the sec-


Fig

.12

.3.

Cor

rela

tion

char

tsh

owin

gth

ere

lati

veag

esof

late

Hem

phil

lian

,B

lanc

an,

and

Irvi

ngto

nian

vert

ebra

tefa

unas

from

the

sout

hern

Rio

Gra

nde

Val

ley

and

Gil

aR

iver

Val

ley

inN

ewM

exic

o,in

clud

ing

the

Hat

ch-R

inco

n,Jo

rnad

a,M

esil

la,

Man

gas,

and

Dun

can

basi

ns.

Oth

erno

tes

asfo

rfi

gure

12.2

.


ond site that records the co-occurrence ofCuvieronius, Stegomastodon, and Mammu-thus, the other being the early IrvingtonianGilliland LF from the Seymour Formation inTexas (Hibbard and Dalquest, 1966). Cuvi-eronius is not particularly age diagnostic inNorth America, as this genus first appears inthe Blancan and survives until the early Ran-cholabrean (Morgan and Hulbert, 1995).However, the association of Stegomastodonand Mammuthus is important biochronolog-ically because these two genera have only alimited period of overlap in the early Irving-tonian, after the arrival of Mammuthus acrossthe Bering Land Bridge from Eurasia (about1.6 Ma) and before the extinction of Stego-mastodon (about 1.2 Ma). The presence ofMammuthus clearly establishes an Irvington-ian age for the Tortugas Mountain LF. At pre-sent there are no confirmed records of mam-moths in North America older than 1.6 Ma(Lucas, 1995, 1996; Cassiliano, 1999). Themammoth teeth from the Tortugas MountainLF, identified as M. imperator by Lucas et al.(1999, 2000), are very similar to mammothteeth from other early Irvingtonian sites, in-cluding M. haroldcooki from Gilliland, Texas(Hibbard and Dalquest, 1966) and Holloman,Oklahoma (Dalquest, 1977) and M. hayifrom Leisey Shell Pit, Florida (Webb andDudley, 1995). The youngest well-dated re-cord of Stegomastodon mirificus is from TuleCanyon in the Texas Panhandle, where thisspecies is associated with mammoths andseveral species of horses in a volcanic ash atthe base of the Tule Formation dated at be-tween 1.3 and 1.2 Ma (Izett, 1977; Tedford,1981; Madden, 1983). An age between 1.6and 1.2 Ma is indicated for the TortugasMountain LF based on the association ofMammuthus and Stegomastodon.

MESILLA BASIN FAUNA A: There are threevertebrate faunas from the Camp Rice For-mation in the southern Mesilla basin, fromChamberino south to Santa Teresa near theborder with Mexico (Vanderhill, 1986). Fau-nas A and B are late Blancan in age, andFauna C is early Irvingtonian. Mesilla BasinFauna A (hereafter shortened to Mesilla A)is the oldest and least well known of thethree southern Mesilla basin faunas, probablybecause exposures of the lower part of thesection are less extensive than in the upper

part of the sequence (Vanderhill, 1986; fig.12.1, site 27). The vertebrate assemblagefrom Mesilla A is composed of only six spe-cies (table 12.1; from Vanderhill, 1986): thecatfish Ictalurus, the softshell turtle Apalone(5 Trionyx), the glyptodont Glyptotherium,the horses Nannippus peninsulatus and Eq-uus cf. E. calobatus, and the llama Hem-iauchenia blancoensis. The presence ofGlyptotherium confirms a late Blancan oryounger age (younger than 2.7 Ma) for thisfauna, as the first appearance of South Amer-ican immigrants, including Glyptotherium, inNorth American faunas defines the beginningof the late Blancan. The presence of Nannip-pus indicates an age greater than 2.2 Ma.

Magnetostratigraphic data for the CampRice Formation strata from which the Mes-illa A fauna was derived further restrict itsage (Vanderhill, 1986). Mesilla A occurs innormally magnetized sediments in the upperGauss Chron between the Kaena Subchron(3.04 Ma) and the Gauss/Matuyama bound-ary (2.58 Ma). Mesilla A is one of only sixsouthwestern Blancan faunas that documentsthe presence in the upper Gauss Chron (be-tween 3.0 and 2.6 Ma) of South Americanimmigrant mammals. Although 2.7 Ma is of-ten cited as the first appearance datum forSouth American immigrants in North Amer-ica, and is used here as the boundary be-tween the medial and late Blancan, the tim-ing of the first appearance in southwesternBlancan faunas of mammals that participatedin the Great American Interchange is notfirmly established, but occurred sometimebetween 3.0 and 2.6 Ma. There are no con-firmed records of Interchange mammals inBlancan faunas north of Mexico that predatethe Kaena Subchron at 3.04 Ma. However,several new records of South American im-migrants from central Mexico appear to beearly Blancan (Miller and Carranza-Casta-neda, 2001, 2002).

MESILLA BASIN FAUNA B: Mesilla BasinFauna B (hereafter shortened to Mesilla B)is the most diverse late Blancan fauna inNew Mexico (fig. 12.1, site 28). Vanderhill(1986: table 1) listed 16 species from MesillaB: two turtles, the aquatic emydid Trachemysand the land tortoise Hesperotestudo; and 14mammals including Glyptotherium arizonae,the mylodont gound sloth Paramylodon cf.


P. harlani, the rabbits Aluralagus virginiaeand a larger Lepus or Sylvilagus, the smallcat cf. Lynx rufus, the sabercat Smilodongracilis, the horses Equus cf. E. calobatusand E. scotti, the large tapir Tapirus haysii,the camelids Blancocamelus meadei, Gigan-tocamelus cf. G. spatula, and Camelops, thedeer Odocoileus, and the gomphothere Cu-vieronius. Our recent fieldwork in the CampRice Formation near La Union has addedfour species of large mammals to the MesillaB fauna (table 12.1).

We recently discovered a new microver-tebrate site near Chamberino in the southernMesilla basin (NMMNH site L-2971), fromthe same stratigraphic level as Vanderhill’sMesilla B. This site occurs stratigraphicallyabout 5 m below the lowest occurrence ofMammuthus in the Chamberino section. TheChamberino microsite is being activelyscreenwashed at the present time. Prelimi-nary identifications add at least 11 species tothe Mesilla B fauna: two snakes, a lizard, asmall passerine bird, and seven mammals in-cluding the mole Scalopus, the ground squir-rel Spermophilus, the pocket gopher Geomys,the heteromyid rodent Dipodomys, the cottonrat Sigmodon, the grasshopper mouse Ony-chomys, and the skunk Spilogale. CombiningVanderhill’s Faunule B with our Chamberinosite, the Mesilla B fauna now has 25 speciesof mammals, making it the most diverseBlancan mammal fauna in New Mexico.

Mesilla B has a diverse assemblage ofmammals, but only a few taxa are age di-agnostic. Many species occur in both lateBlancan and early Irvingtonian and youngerfaunas. Vanderhill (1986) correlated MesillaB with the transitional interval between theBlancan and Irvingtonian (2.2–1.8 Ma). Twogenera typical of the Blancan, the giant cam-els Blancocamelus and Gigantocamelus, oc-cur in Mesilla B. The presence of the SouthAmerican immigrant xenarthrans Glyptoth-erium arizonae and Paramylodon cf. P. har-lani confirms that Mesilla B is late Blancanor younger. G. arizonae is supposedly re-stricted to early Irvingtonian sites elsewherein the southwest (Gillette and Ray, 1981).However, the type locality of G. arizonae,Curtis Ranch in the San Pedro Valley of Ar-izona, although considered earliest Irvington-ian by most workers (e.g., Lundelius et al.,

1987; Repenning, 1987), is best regarded aslatest Blancan owing to the absence of Mam-muthus and other typical Irvingtonian genera(Lindsay et al., 1990). There are also lateBlancan records of G. arizonae from Florida(Morgan and Hulbert, 1995). The rabbit Al-uralagus virginiae appears to be restricted toBlancan/Irvingtonian transitional faunas. Theonly other faunas where A. virginiae hasbeen identified (referred to Hypolagus virgi-niae by Tomida, 1987), Curtis Ranch and theSan Simon Power Line, both in southern Ar-izona, are similar in age to Mesilla B. Smi-lodon gracilis and Tapirus haysii are typicalof early Irvingtonian faunas, but both areknown from the late Blancan. Previoussouthwestern records of S. gracilis are re-stricted to the early Irvingtonian, but this sa-bercat occurs in several Florida late Blancanfaunas (Berta, 1987; Morgan and Hulbert,1995). T. haysii is known from late Blancanfaunas in Texas and Colorado (Strain, 1966;Hager, 1974; Hulbert, 1995).

Magnetostratigraphic data for Mesilla B(Vanderhill, 1986) indicate that the zone con-taining this fauna spans the time period fromthe Gauss/Matuyama boundary to the Oldu-vai Subchron (between about 2.6 and 1.8Ma). Faunal evidence suggests that MesillaB falls in the younger half of this interval,as typical Blancan taxa that went extinct byabout 2.2 Ma (Hypolagus, Nannippus, andRhynchotherium) are absent from this fauna.Pending the discovery of additional age-di-agnostic taxa in the Mesilla B fauna, partic-ularly among small mammals, this fauna ishere considered to be latest Blancan (latestPliocene) in age, between 2.2 and 1.8 Ma.

MESILLA BASIN FAUNA C: The uppermostportion of the Camp Rice Formation in thesouthern Mesilla basin (fig. 12.1, site 29)contains Mammuthus, and is thus Irvington-ian or younger in age. Mesilla Basin FaunaC (hereafter shortened to Mesilla C) is cor-relative with the early Irvingtonian TortugasMountain LF near Las Cruces (Lucas et al.,1999, 2000) in the northern Mesilla basin.Among Irvingtonian faunas in New Mexico,Mesilla C has the most diverse sample oflarge vertebrates (table 1, from Vanderhill,1986), consisting of 17 species: the land tor-toises Gopherus and Hesperotestudo and 15species of mammals, including Glyptother-


ium arizonae; Paramylodon harlani; the me-galonychid ground sloth Megalonyx wheatle-yi; the beaver Castor canadensis; the wolfCanis armbrusteri; a smaller coyote-like Ca-nis sp.; the bobcat Lynx rufus; three horses,Equus cf. E. calobatus, E. scotti, and a largeEquus, Camelops cf. C. hesternus; the cervidNavahoceros lascrucensis; the deer Odoco-ileus; the gomphothere Cuvieronius tropicus;and the mammoth Mammuthus cf. M. meri-dionalis.

The first appearance of Mammuthus inNorth America as an immigrant from Eurasiaoccurred sometime around 1.6 Ma (Lucas,1995, 1996; Cassiliano, 1999). The primitivemammoth Mammuthus meridionalis, identi-fied from Mesilla C (Vanderhill, 1986), oc-curs only in early Irvingtonian faunas, and isquickly replaced by (or evolved into) moreadvanced mammoths variously referred to M.haroldcooki, M. hayi, and M. imperator,which are also present in the early Irvington-ian. Although Glyptotherium arizonae is sup-posedly restricted to early Irvingtonian fau-nas in the southwestern United States (Gil-lette and Ray, 1981), fossils referred to thisspecies from Mesilla B and Virden appear tobe latest Blancan. The large wolflike canidCanis armbrusteri is found only in Irving-tonian faunas, with the oldest record of thisspecies from the early Irvingtonian LeiseyShell Pit LF in Florida (Berta, 1995). Theliving beaver Castor canadensis is restrictedto Irvingtonian and younger faunas in NorthAmerica. A supposed late Blancan record ofC. canadensis from the Haile 15A LF inFlorida (Robertson, 1976) is based on a fe-mur that is not diagnostic at the species level.

Mesilla C is most similar to early Irving-tonian faunas from the southern Great Plains,such as Gilliland and Rock Creek in Texas(Hibbard and Dalquest, 1966) and Hollomanin Oklahoma (Dalquest, 1977), that containGlyptotherium arizonae, Paramylodon har-lani, Equus scotti, E. calobatus, and Mam-muthus sp. Magnetostratigraphy for the in-terval that produces the Mesilla C fauna(Vanderhill, 1986) suggests correlation withthe upper Matuyama Chron, spanning thetime interval from just after the Olduvai Sub-chron (1.81 Ma) to just prior to the JaramilloSubchron (1.07 Ma). Mack et al. (1996) ob-tained Ar/Ar dates on three pumice beds

from the Camp Rice Formation near LaUnion, in the vicinity where many of the fos-sils from both Mesilla B and C were col-lected. A pumice dated at 1.59 Ma occursabout 30 m below the La Mesa surface (localtop of the Camp Rice Formation in the LaUnion section) and a pumice dated at 1.32Ma occurs about 10 m below the top of thesection (Mack et al., 1996: fig. 2). Althoughthese radioisotopic dates cannot currently beprecisely correlated with the magnetostratig-raphy and biostratigraphy, it appears that allof the Mesilla C fossils were collected fromabove the 1.59 Ma pumice date, which pro-vides a maximum age for this fauna. It islikely that some fossils assigned to MesillaC were collected from strata above the 1.32Ma pumice date. The combination of bio-stratigraphy, magnetostratigraphy, and radio-isotopic dates suggests an age between 1.6and 1.1 Ma for Mesilla C (Vanderhill, 1986;Mack et al., 1996).

MANGAS BASIN

BUCKHORN: The Buckhorn LF is derivedfrom 14 sites located between 3 and 10 kmnorthwest of Buckhorn in northern GrantCounty, southwestern New Mexico (Morganet al., 1997; fig. 12.1, site 30). The fossilsoccur in unconsolidated sands, silts, andmuds through a stratigraphic interval ofabout 20 m in the upper part of the GilaGroup in the Mangas basin. The abundanceof aquatic vertebrates in several of the Buck-horn sites, including fish, frogs, flamingos,rails, and ducks, as well as the lithology ofthe sediments, suggests a freshwater deposi-tional environment, possibly a large lake.The Buckhorn LF is the most diverse Blan-can vertebrate faunal assemblage knownfrom New Mexico, composed of 33 species,including 14 lower vertebrates and 19 mam-mals (Morgan et al., 1997). The nonmam-mals include three species of small fish, thefrog Rana, the salamander Ambystoma, twounidentified colubrid snakes, a lizard, and sixbirds—the flamingo Phoenicopterus, twoducks, a rail, the turkey cf. Meleagris, and asmall perching bird. The mammalian faunaof 19 species includes a microchiropteranbat; a rabbit; the ground squirrel Spermophi-lus cf. S. bensoni; Repomys cf. R. panacen-


sis; the vole Mimomys poaphagus, Peromys-cus sp., and Baiomys sp.; four carnivores in-cluding the badger Taxidea, a bear, a smallfeline, and a large machairodontine; twohorses, Nannippus peninsulatus and Equussimplicidens; a peccary, three camelids, Ca-melops sp., Hemiauchenia blancoensis, anda small Hemiauchenia, an indeterminate ru-minant, and Stegomastodon.

Many of the mammals from the BuckhornLF are indicative of a Blancan age, includingMimomys, Repomys cf. R. panacaensis, Nan-nippus peninsulatus, Equus simplicidens, andHemiauchenia blancoensis. Several taxa al-low for a more precise placement within theBlancan. The presence of a primitive speciesof the arvicoline rodent Mimomys and the ab-sence of Neotropical immigrants suggest apre-late Blancan age (older than 2.7 Ma).The occurrence of Equus simplicidens and alarge species of Mimomys (subgenus Ogmo-dontomys) excludes very early Blancan fau-nas. The evolutionary stage of two of theBuckhorn rodents, Mimomys (Ogmodonto-mys) poaphagus and Repomys cf. R. pana-caensis, is most consistent with a late earlyBlancan age (between about 4.2 and 3.6 Ma;Blancan II of Repenning, 1987) for theBuckhorn LF.

The Buckhorn LF and the Truth or Con-sequences LF from the central Rio GrandeValley both appear to be early Blancan in ageon the basis of comparisons with early Blan-can faunas outside of New Mexico; however,the mammalian faunas from these two siteshave virtually no age-diagnostic taxa in com-mon, particularly among the small mammals.Mimomys, the extinct ‘‘cricetid’’ genus Re-pomys, and the tiny sigmodontine Baiomysoccur in the Buckhorn LF, whereas the Truthor Consequences LF is dominated by thewood rat Neotoma, the cotton rat Sigmodon,and the small extinct sigmodontine genus Ja-cobsomys. The Buckhorn and Truth or Con-sequences faunas must have sampled differ-ent habitats or perhaps differ enough in ageto have allowed significant change in thesmall mammal fauna. Other early Blancanfaunas that are broadly correlative withBuckhorn are the Verde LF in Arizona (Cza-plewski, 1987, 1990), the Panaca LF in Ne-vada (May, 1981; Mou, 1997, 1999), and theRexroad 3 and Fox Canyon faunas from

Kansas (Hibbard, 1938, 1941, 1950, 1967;Repenning, 1987).

There are currently no radioisotopic datesor magnetostratigraphic data that would pro-vide additional information on the age of theBuckhorn LF. There are several volcanic ashbeds in the Buckhorn section, but they aretoo altered to provide accurate radioisotopicdates. The latest Hemphillian Walnut CanyonLF occurs in Gila Group strata about 25 kmsoutheast of the Buckhorn LF (Morgan et al.,1997; fig. 12.1, site 31). The latest Hemphil-lian age (earliest Pliocene; 5.0–4.5 Ma) ofthe Walnut Canyon LF provides a maximumage for the Buckhorn LF. These two faunashave no taxa in common, indicating that theHemphillian/Blancan boundary occurs some-where in the section separating them. Furtherfieldwork in the region between Buckhornand Walnut Canyon should allow a more pre-cise stratigraphic placement of these two fau-nas.

DUNCAN BASIN

PEARSON MESA: Exposures on PearsonMesa south of the Gila River in the Duncanbasin along the New Mexico-Arizona borderhave produced a diverse assemblage of lateBlancan vertebrate fossils from strata of theGila Group (fig. 12.1, sites 32, 33). Most ofPearson Mesa is located in Hidalgo Countyin southwestern New Mexico, but the north-western point of the mesa extends intoGreenlee County in southeastern Arizona.About three-fourths of the 76 NMMNH fos-sil sites located on Pearson Mesa are in NewMexico and the rest are in Arizona. Thestratigraphic section at Pearson Mesa con-sists of more than 60 m of sandstones, mud-stones, and sedimentary breccias referred tothe Gila Group. The lower 15 m of this sec-tion contains the three-toed horse Nannippuspeninsulatus and the horse Equus simplici-dens, together with rarer specimens of manyother taxa, the most significant of which isthe mylodont ground sloth Glossotherium cf.G. chapadmalense. This assemblage, thePearson Mesa LF (Tomida, 1987; Morganand Lucas, 2000b; fig. 12.1, site 32), is in-dicative of a late Blancan age. A latest Blan-can fauna, the Virden LF (fig. 12.1, site 33),


occurs in the upper 20 m of the section atPearson Mesa, and is discussed below.

The Pearson Mesa LF consists of 16 spe-cies of vertebrates: the land tortoise Gopher-us, a large and a small species of the landtortoise Hesperotestudo, the box turtle Ter-rapene, a heron, and 11 mammals, includingGlossotherium cf. G. chapadmalense; a smallcat and a larger machairodontine sabercat;the pocket gopher Geomys (Nerterogeomys)cf. G. persimilis; the horses Nannippus pen-insulatus, Equus cumminsii, E. scotti, and E.simplicidens; the peccary Platygonus bical-caratus; the camelid Hemiauchenia blan-coensis; and the gomphothere Stegomasto-don rexroadensis. The presence of Nannip-pus in the Pearson Mesa LF indicates an agegreater than 2.2 Ma, whereas Glossotheriumdoes not appear in North American faunasuntil the late Blancan, indicating an age lessthan 2.7 Ma. Other taxa from the PearsonMesa LF that provide some indication of ageinclude Geomys (N.) persimilis, Platygonusbicalcaratus, and Stegomastodon rexroad-ensis. G. (N.) persimilis occurs in medialBlancan through early Irvingtonian sites inthe southwestern United States. Tomida(1987) noted that the presence of this pocketgopher in the lower part of the Pearson Mesasection suggested placement in the upper-most Gauss Chron. Platygonus bicalcaratusapparently is restricted to medial and lateBlancan faunas, and Stegomastodon rexroad-ensis occurs in the early and medial Blancan.The mandible of Stegomastodon upon whichthis record is based (F:AM 23338) is froman imprecisely located site in the vicinity ofPearson Mesa, and is of unknown strati-graphic position. A mandible of similar mor-phology, referred to S. rexroadensis, occursin the medial Blancan Cuchillo Negro CreekLF (Lucas and Oakes, 1986). The medialBlancan Duncan Fauna is located near Dun-can, Arizona, less than 10 km northwest ofPearson Mesa (Tomida, 1987), and thus it ispossible that the S. rexroadensis mandiblewas derived from lower in the Gila Groupsection than strata that produce the PearsonMesa LF.

The association of Nannippus with Glos-sotherium provides the most significant bio-stratigraphic information regarding the age ofthe Pearson Mesa LF. The first appearance of

South American immigrants in North Amer-ican faunas, following the onset of the GreatAmerican Interchange at about 2.7 Ma, de-fines the beginning of the late Blancan. Theonly time interval during which these twogenera coexisted in southwestern faunas wasbetween 2.7 Ma (the beginning of the Inter-change) and 2.2 Ma (the Nannippus extinc-tion datum of Lindsay et al., 1984). A paleo-magnetic section from Pearson Mesa (Tom-ida, 1987) further restricts the age of the low-er portion of the section, including thePearson Mesa LF, to the upper Gauss Chron(3.0–2.6 Ma). Combining the biostratigraph-ic and magnetostratigraphic data for thePearson Mesa LF would seem to tightly con-strain the age of this fauna between 2.7 Ma(earliest appearance of Glossotherium) and2.6 Ma (Gauss/Matuyama boundary). Al-though the timing of the first arrival of SouthAmerican immigrants in North America isnot precisely known, Pearson Mesa is im-portant because it is one of only six sites inthe southwestern United States that recordsthe presence of South American Interchangemammals in the Gauss Chron, indicating anage greater than 2.6 Ma.

VIRDEN: A substantial thickness (about 30m) of Gila Group strata in the middle of thePearson Mesa section has not yet producedfossils, including a 9-m-thick breccia at thetop of this unfossiliferous interval that mayrepresent a hiatus (Morgan and Lucas,2000b). Just above this breccia, at about the45 m level in the section and continuing forabout the next 10 m, vertebrate fossils occurat several localities on Pearson Mesa. Thisfauna differs significantly from the underly-ing Pearson Mesa LF, and is here named theVirden Local Fauna for the nearby village ofVirden, New Mexico (fig. 12.1, site 33). Ex-posures in the upper portion of the PearsonMesa section are not as extensive and tendto be more vertical than lower in the section,and consequently the Virden LF is not asabundant or diverse as the Pearson Mesa LF.Nonetheless, the presence of Glyptotheriumarizonae and the absence of Nannippus inthe Virden LF indicate that this fauna isyounger than the Pearson Mesa LF, either lat-est Blancan or earliest Irvingtonian in age.The only taxa these faunas share are a largeland tortoise and Equus scotti.


The Virden LF consists of seven species:the land tortoise Hesperotestudo and sixmammals, including Glyptotherium arizonae,the coyote-like canid Canis lepophagus, Eq-uus scotti, Camelops, a small Hemiauchenia,and an indeterminate proboscidean. Theglyptodonts in the Virden LF, represented byosteoderms, a cranial fragment, and severalpostcranial elements, are referable to thelarge species G. arizonae. Glyptodonts firstappear in southwestern faunas in the earlylate Blancan (upper Gauss Chron) in sitesequivalent in age to the Pearson Mesa LF(e.g., Hudspeth and Cita Canyon in Texasand 111 Ranch in Arizona), but these occur-rences represent the smaller species G. tex-anum. Glyptodonts are unknown from thePearson Mesa LF. Although previous recordsof G. arizonae indicated that this species wasrestricted to the early Irvingtonian in thesouthwestern United States (Gillette and Ray,1981), there are now late Blancan records ofthis species from Curtis Ranch in Arizona,Mesilla B, and Virden, as well as Florida(Morgan and Hulbert, 1995).

Associated mandibles of a medium-sizedcanid, similar in size and morphology to thecoyote-sized species Canis lepophagus, werefound in association with Glyptotherium os-teoderms in the upper portion of the PearsonMesa section. C. lepophagus is restricted tothe Blancan, including the late Blancan CitaCanyon and Red Light faunas in Texas (Ak-ersten, 1972) and the late Blancan 111 Ranchfauna in Arizona (Galusha et al., 1984; Tom-ida, 1987). A pair of lower jaws from Virdenrepresents a small species of Hemiauchenia.These mandibles are from an adult with well-worn teeth, but are very small compared toother known species of Hemiauchenia, suchas the Blancan H. blancoensis and the Ir-vingtonian and Rancholabrean H. macroce-phala. A small Hemiauchenia occurs in sev-eral New Mexico Blancan faunas, includingCuchillo Negro Creek, Tonuco Mountain,and Buckhorn, as well as two early Irving-tonian sites in Florida (Morgan and Hulbert,1995). Equus scotti is one of the most com-mon horses found in southwestern early Ir-vingtonian faunas, but this species also oc-curs in medial and late Blancan sites in NewMexico.

The presence of Glyptotherium arizonae

and the absence of diagnostic Blancan indi-cators (e.g., Nannippus) suggests that theVirden LF is distinctly younger than the un-derlying Pearson Mesa LF, probably eitherlatest Blancan or earliest Irvingtonian (be-tween 2.2 and 1.6 Ma). The presence of Ca-nis lepophagus, a species unknown from theIrvingtonian, suggests that a latest Blancanage is more likely. Tomida’s (1987) PearsonMesa paleomagnetic stratigraphy does not in-clude the upper 20 m of the section (Morganand Lucas, 2000b), and thus we currentlyhave no magnetostratigraphic data for thisfauna. Paleomagnetic samples from the up-per portion of the section recently collectedby G. Mack should help clarify the age ofthe Virden LF.

BIOCHRONOLOGY ANDCORRELATION

There are 24 Blancan and 7 Irvingtoniansites in New Mexico that have produced fos-sil mammals. Four or more species of mam-mals are known from 15 of the Blancan and4 of the Irvingtonian sites (faunal lists in ta-bles 12.1 and 12.2, respectively). Throughoutthe preceding discussion, we have providedinformation on the ages of the 31 sites andthe biochronology of the individual taxa.Here we summarize the biochronology ofNew Mexico Blancan and Irvingtonian sites,with correlation to well-known faunas fromelsewhere in western North America. Thesedata are preliminary because we are still ac-tively involved in fieldwork at several of thericher sites, particularly those with diversesmall mammal faunas (e.g., Buckhorn,Chamberino, and Truth or Consequences).New taxa are still being added to the variousfaunal lists, but for most of the sites listed intables 12.1 and 12.2, enough taxa are presentto provide an accurate indication of age, atleast within the major subdivisions of the twoNALMAs (e.g., medial Blancan, early Ir-vingtonian). We also review all relevant ra-dioisotopic dates and magnetostratigraphicdata pertaining to New Mexico Blancan andIrvingtonian sites. The correlation charts infigures 12.2 and 12.3 summarize the currentstate of our knowledge on the age of the sitesdiscussed in the text. Figure 12.4 correlatesthe New Mexico Blancan and Irvingtonian


Fig

.12

.4.

Cor

rela

tion

char

tsh

owin

gth

ere

lati

veag

esof

late

Hem

phil

lian

,B

lanc

an,

and

Irvi

ngto

nian

vert

ebra

tefa

unas

from

New

Mex

ico

com

pare

dto

faun

asof

sim

ilar

age

from

Ari

zona

and

Tex

as.

Oth

erno

tes

asfo

rfi

gure

12.2

.


faunas with well-known faunas from Arizonaand Texas. Not all of the Blancan and Ir-vingtonian sites from New Mexico are in-cluded in the correlation charts. All sites list-ed in tables are included in the correlationcharts, as well as selected faunas with fewerthan four mammals that contain age-diag-nostic taxa.

With two exceptions, all Pliocene verte-brate faunas in New Mexico are Blancan,ranging in age from about 4.5 to 1.8 Ma.There is a restricted interval of time in theearliest Pliocene (between 5.3 and 4.9–4.5Ma, depending on the placement of the Hem-phillian/Blancan boundary) that is includedwithin the next older NALMA, the Hem-phillian. Most Hemphillian faunas are lateMiocene in age (9.0–5.3 Ma), including thewell-known faunas from the type area of theChamita Formation in the Espanola basin innorthern New Mexico (MacFadden, 1977;Tedford, 1981), which are late early to earlylate Hemphillian (about 7–5.5 Ma). The Wal-nut Canyon LF from the Gila Group in theMangas basin in southwestern New Mexico(Morgan et al., 1997; fig. 12.1, site 31; figs.12.3, 12.4) has two horses, Astrohippus sto-cki and Dinohippus mexicanus, that are verysimilar to horses from the latest Hemphillian(earliest Pliocene) Yepomera Fauna fromChihuahua in northern Mexico (Lance, 1950;MacFadden, 1984). The lower Puye Forma-tion in the Espanola basin (fig. 12.1, site 2)has produced a palate with most of the uppercheek teeth of D. mexicanus, indicating thatat least part of the Puye Formation is latestHemphillian in age as well (figs. 12.2, 12.4).

The Mangas Basin in southwestern NewMexico is the only place in the state wherea Blancan fauna occurs in stratigraphic su-perposition above a Hemphillian fauna. Wemeasured two stratigraphic sections in GilaGroup sediments in the Mangas Basin inGrant County (Morgan et al., 1997), a 76-msection incorporating the latest HemphillianWalnut Canyon Horse Quarry (NMMNH siteL-2922) and a 57-m section incorporatingseveral sites included in the early BlancanBuckhorn LF (in particular, the Buckhornmicrovertebrate site, NMMNH site L-2912).We have not yet been able to correlate thesetwo sections, although the Walnut Canyonfossils occur at least 50 m below the lowest

Buckhorn sites in the composite Gila Groupsection in the central Mangas basin. TheWalnut Canyon LF compares closely to theYepomera Fauna, one of the youngest knownHemphillian faunas (Lindsay et al., 1984),whereas the Buckhorn LF is early, but notearliest, Blancan. These age relationshipssuggest two possibilities: (1) there may be ahiatus in the Gila Group section or (2) theremay be an older, and as yet undiscovered,earliest Blancan fauna in the intervening un-measured section. Although separated by lessthan 1 m.y., the Walnut Canyon and Buck-horn faunas have no taxa in common, indi-cating that the major extinction event docu-mented at the Hemphillian/Blancan bound-ary (Lindsay et al., 1984; Tedford et al.,1987) occurs somewhere in the section be-tween these two sites. The horses Astrohip-pus and Dinohippus are common in the Wal-nut Canyon LF, but both disappear at the endof the Hemphillian. The microtine rodent Mi-momys, a Eurasian immigrant and one of thegenera whose first appearance in NorthAmerica defines the beginning of the Blan-can (Repenning, 1987; Tedford et al., 1987),is one of the most common mammals in theBuckhorn LF.

Repenning (1987) subdivided the Blancaninto five ‘‘subages’’ (Blancan I–V) based onmicrotine (5 arvicoline) rodent biochronol-ogy. Although Repenning’s system is veryuseful if a site contains one or preferablymore species of microtine rodents, he pro-vided only limited data for other mammalgroups. Only one Blancan fauna in NewMexico, the Buckhorn LF, contains micro-tines. Faunas dominated by large mammals,which include most Blancan faunas fromNew Mexico, are difficult to correlate usingRepenning’s microtine biochronology. Lun-delius et al. (1987) and Woodburne andSwisher (1995) used a two-part subdivisionof the Blancan: early Blancan (5 Rexroadianof Schultz et al., 1978; BL1 of Woodburneand Swisher, 1995) and late Blancan (5 Se-necan of Schultz et al., 1978; BL2 of Wood-burne and Swisher, 1995). The boundary be-tween their early and late Blancan corre-sponds to the arrival at about 2.7 Ma of im-migrant xenarthrans and caviomorph rodentsfrom South America and several microtinerodents from Eurasia. We have found it use-


ful, following Tedford (1981), to subdividethe early Blancan of Lundelius et al. (1987)and Woodburne and Swisher (1995), a timeinterval of nearly 2 Ma (between about 4.5and 2.7 Ma), into the early and medial Blan-can, with the boundary between these suba-ges corresponding to the boundary betweenthe Gilbert and Gauss Chrons at about 3.6Ma. Where possible, we correlate New Mex-ico Blancan and Irvingtonian faunas withRepenning’s microtine biochronology.

First appearances of Eurasian immigrantmammals have been used to define the be-ginning of the Blancan (between 4.9 and 4.3Ma) in North America, including: the mus-telid Trigonictis, the hyaena Chasmaporthe-tes, the bear Ursus, the microtine rodents Mi-momys and Nebraskomys, and the cervidsBretzia and Odocoileus (Lundelius et al.,1987; Tedford et al., 1987; Woodburne andSwisher, 1995). However, according to Lind-say et al. (1984), some of these first appear-ances occurred later, at about 3.7 Ma, whichthey designated the Trigonictis appearancedatum. In addition to Trigonictis, other gen-era they listed as first appearances about 3.7Ma include Chasmaporthetes, Ursus, the rab-bits Nekrolagus and Pratilepus, the pocketgopher Thomomys, the wood rat Neotoma,the muskrat Pliopotamys, the peccary Pla-tygonus, the camel Camelops, and the mas-todont Mammut.

In part, the discrepancy in the ages of thefirst occurences of certain genera used to de-fine the Blancan is related to differences ofopinion regarding the age and correlation ofthe White Bluffs LF in Washington (Gustaf-son, 1978, 1985), the earliest Blancan faunathat contains a diverse sample of both largeand small mammals. Most other very earlyBlancan faunas (e.g., Concha in Chihuahua,Mexico; Saw Rock Canyon, Kansas; andVerde, Arizona) consist predominantly ofsmall mammals (Lindsay et al., 1984; Cza-plewski, 1987, 1990; Lundelius et al., 1987;Repenning, 1987). Lindsay et al. and Lun-delius et al. considered White Bluffs to beearly Blancan (3.9–3.7 Ma; Blancan II of Re-penning, 1987), but not earliest Blancan, anda correlative of the Fox Canyon Fauna inKansas and slightly older than the HagermanFauna in Idaho. Repenning thought WhiteBluffs was considerably older (about 4.3 Ma,

Blancan I). If the White Bluffs LF is 4.3 Main age, then this fauna represents the oldestdocumented occurrence of many of the gen-era listed above, including Trigonictis, Ur-sus, Nekrolagus, Thomomys, Platygonus, andMammut. The first appearance of Neotomaappears to be in the Saw Rock Canyon LFin Kansas, which most workers (e.g., Lun-delius et al., 1987; Repenning, 1987) regardas one of the earliest Blancan faunas in NorthAmerica (early Blancan I, 4.8–4.3 Ma).Many of the genera used to define the begin-ning of the Blancan occur in the Anza-Bor-rego Desert stratigraphic sequence, but havetheir lowest occurrence well above the Hem-phillian/Blancan boundary (Cassiliano,1999). Cassiliano suggested that the loweststratigraphic occurrence of the cotton rat Sig-modon in the Anza-Borrego sequence atabout 4.3 Ma may be close to the Hemphil-lian/Blancan boundary.

Two of the most diverse Blancan faunasfrom New Mexico, the Truth or Consequenc-es LF from the Palomas Formation in the RioGrande Valley (Repenning and May, 1986)and the Buckhorn LF from the Gila Groupin the Gila River Valley (Morgan et al.,1997), are early Blancan in age. Even thoughthese two faunas have almost no age-diag-nostic mammals in common, comparisonswith Blancan faunas outside of New Mexicoindicate that the Truth or Consequences andBuckhorn faunas are similar in age (late earlyBlancan 5 Blancan II, about 4.2–3.8 Ma).

Repenning and May (1986) considered theTruth or Consequences LF to be early Blan-can based on the somewhat more primitivenature of its mammalian fauna compared tothe Fox Canyon and Rexroad 3 faunas fromKansas. The primitive wood rat Neotoma(subgenus Paraneotoma) from Truth or Con-sequences is intermediate in size between thesmaller N. sawrockensis from the earliestBlancan Saw Rock Canyon LF and the largerN. quadriplicata from early Blancan Rexroad3 (Repenning and May, 1986). The Truth orConsequences Neotoma is similar to N.vaughani from the early Blancan (Blancan II,about 4.2 Ma) Verde LF in Arizona (Cza-plewski, 1990). The small sigmodontine ro-dent Jacobsomys from Verde appears to bepresent at Truth or Consequences (Czaplew-ski, 1987). The deer from Truth or Conse-


quences, Odocoileus brachyodontus, wasfirst described from Fox Canyon (Oelrich,1953). Truth or Consequences shares threespecies of small mammals with the earlyBlancan Rexroad 3 Fauna, Notolagus lepus-culus, Geomys minor, and Sigmodon medius.G. minor and S. medius also occur in theVerde LF, which seems to have the closestfaunal similarity with Truth or Consequenc-es.

The Truth or Consequences LF occurs innormally magnetized sediments that werecorrelated with the Nunivak Subchron of theGilbert Chron (Repenning and May, 1986).These authors gave an age range of 4.20–4.05 Ma for the Nunivak, but the currentlyrecognized age range of this subchron issomewhat older, from 4.62–4.48 Ma (Berg-gren et al., 1995). A K/Ar date of 4.5 Ma ona basalt flow below or within the lowermostPalomas Formation provides a maximum agefor the Truth of Consequences LF (Seager etal., 1984; Mack et al., 1998). A more com-plete magnetostratigraphic section must beobtained for the strata of the Palomas For-mation containing the Truth or Consequencessite before this fauna can be accurately cor-related to the geomagnetic polarity time scale(GPTS). We suspect that the Truth or Con-sequences LF actually may correlate to thenext youngest normal subchron in the Gil-bert, the Cochiti, with an age range of 4.29–4.18 Ma (Berggren et al., 1995). Repenning(1987) considered Truth or Consequences tobe similar in age to Verde, somewhat youn-ger than White Bluffs, and slightly older thanRexroad 3 and Fox Canyon.

The Buckhorn LF has 18 species of mam-mals compared to 15 species from the Truthor Consequences LF; however, many of theBuckhorn taxa are not age diagnostic or areidentified only to the family or genus level(Morgan et al., 1997). The most age-diag-nostic mammals from the Buckhorn LF arethe rodents Mimomys (Ogmodontomys)poaphagus and Repomys cf. R. panacensis.The Buckhorn Mimomys is most similar toM. poaphagus from Fox Canyon and Rex-road 3 (Hibbard, 1941, 1950; Zakrzewski,1967) and Verde (Czaplewski, 1990), largerthan M. panacaensis from the Panaca LF inNevada, and differing from the latter speciesin certain dental features (Mou, 1997). A sin-

gle tooth of Repomys from Buckhorn is sim-ilar to R. panacaensis from Panaca (May,1981). The Buckhorn LF is most similar tolate early Blancan (Blancan II of Repenning,1987) faunas such as Fox Canyon, Rexroad3, and Verde, and appears to be somewhatyounger than early Blancan (Blancan I) fau-nas such as Panaca, White Bluffs, and SawRock Canyon. Repenning (1987) placed thePanaca LF in the medial Blancan (BlancanIII, about 3.3 Ma), whereas Mou (1997,1999) considered Panaca to be much older,early Blancan I (4.9–4.6 Ma). There are noother geochronologic data associated withthe Buckhorn LF that would help determineits age. The stratigraphic section that pro-duced the Buckhorn LF contains several vol-canic ash beds, but these are too highly al-tered for radioisotopic dating. In the near fu-ture, we hope to obtain magnetostratigraphicdata for the Gila Group section containingboth the early Blancan Buckhorn LF and thelatest Hemphillian Walnut Canyon LF.

Three faunas derived from the PalomasFormation in the Rio Grande Valley, Cuchi-llo Negro Creek, Elephant Butte Lake, andPalomas Creek, are considered medial Blan-can following Tedford (1981) and Lucas andOakes (1986), although the presence of thelarge canid Borophagus hilli from CuchilloNegro Creek (see discussion below) may beindicative of an early Blancan age (Wang etal., 1999). The Elephant Butte Lake andCuchillo Negro Creek faunas consist almostentirely of large mammals, and thus havefew taxa in common with the Truth or Con-sequences LF. They share two species, Equussimplicidens, found throughout much of theBlancan, and Stegomastodon rexroadensis,restricted to early and medial Blancan fau-nas. Borophagus hilli from Cuchillo NegroCreek, and tentatively identified from Truthor Consequences, occurs primarily in lateHemphillian and early Blancan faunas (e.g.,Saw Rock Canyon and White Bluffs), but isknown from at least one medial Blancan fau-na, Hagerman, Idaho (Wang et al., 1999).Tedford placed the Elephant Butte Lake sitesin the medial Blancan because of their strati-graphic association with a basalt flow fromMitchell Point at the northern end of Ele-phant Butte Lake (K/Ar date of 2.9 6 0.3Ma; Bachman and Mehnert, 1978). Lucas


and Oakes (1986) assigned the Cuchillo Ne-gro Creek LF to the medial Blancan, and cor-related this fauna with Rexroad and Benson.

The Palomas Creek LF shares one speciesof small mammal, Sigmodon medius, withthe Truth or Consequences LF, but S. mediusalso occurs in medial Blancan faunas, in-cluding the type locality, Benson, Arizona(Martin, 1979). A mandible from PalomasCreek is the only record of the extant sub-genus of Geomys known from the Blancanof New Mexico. Other mammals from thisfauna indicative of a Blancan age are Nan-nippus peninsulatus, a large Camelops, andMammut raki. The presence of Nannippusand absence of Neotropical immigrants sug-gest a pre-late Blancan age (older than 2.7Ma), whereas the presence of Camelops in-dicates a post-early Blancan (younger than3.6 Ma). Mammut is rare in the Blancan, butis known from the early Blancan WhiteBluffs LF and the medial Blancan HagermanFauna. A magnetostratigraphic section fromPalomas Creek suggests the fossils camefrom strata referred to the upper Gauss Chron(Mack et al., 1993), indicating a medialBlancan age (between 3.0 and 2.7 Ma) forthe Palomas Creek LF.

Further study of the mammalian taxa andother geochronologic data should eventuallyclarify the age relationships among the fourvertebrate faunas from the Palomas Forma-tion in the vicinity of Elephant Butte Lake,including Truth or Consequences, ElephantButte Lake, Cuchillo Negro Creek, and Pal-omas Creek. The stratigraphic sections con-taining these four faunas have not been pre-cisely correlated to one another to determinetheir relative positions within the PalomasFormation and their stratigraphic positionwith respect to relevant radioisotopic dates.We hope to obtain detailed magnetostrati-graphic sections for the individual sites con-taining Blancan faunas.

Five other sites from the Rio Grande Val-ley, Pajarito, Belen, Arroyo de la Parida,Hatch, and Tonuco Mountain (fig. 12.1), aremedial Blancan in age (3.6–2.7 Ma). In ad-dition to mammalian fossils, three have as-sociated magnetostratigraphy and/or radio-isotopic dates. The Pajarito LF is not diverse,but contains Geomys (Neterogeomys) cf. G.paenebursarius and Camelops, and is direct-

ly associated with an Ar/Ar date of 3.12 Maon pumice (Maldonado et al., 1999), estab-lishing a medial Blancan age.

Four species of mammals from the BelenLF provide an indication of age (Morgan andLucas, 2000a). A mole mandible is most sim-ilar to Scalopus (Hesperoscalops) blancoen-sis from the late Blancan Blanco LF in Texas(Dalquest, 1975). Geomys (Neterogeomys)paenebursarius also occurs in the Pajaritoand Hatch faunas, as well as in two lateBlancan faunas in southwestern Texas(Strain, 1966; Akersten, 1972). Equus calo-batus is known elsewhere in New Mexicofrom the late Blancan Santo Domingo LFand from late Blancan and early Irvingtonianfaunas in the Mesilla basin (Tedford, 1981;Vanderhill, 1986). Stegomastodon mirificusis restricted to medial Blancan through earlyIrvingtonian faunas. Two mammals from Be-len do not occur elsewhere prior to the lateBlancan (S. blancoensis and E. calobatus),whereas two other species (G. paenebursar-ius and S. mirificus) are known from medialBlancan faunas. The similarity in stratigraph-ic occurrence to the nearby Pajarito LF andthe absence of South American immigrantsindicates a medial Blancan age is more likely(between 3.1 and 2.7 Ma).

The Arroyo de la Parida LF from the Pal-omas Formation in the Socorro basin has fivespecies of mammals that are restricted to theBlancan (Morgan et al., 2000), Megalonyxleptostomus, Equus cumminsii, E. simplici-dens, a large Camelops, and Rhynchotheriumfalconeri. Early Blancan can be ruled out bythe presence of E. cumminsii, E. scotti, andCamelops, all of which first appear duringthe medial Blancan. Rhynchotherium becameextinct in the late Blancan at about 2.2 Ma.The absence of South American immigrantssuggests an age greater than 2.7 Ma. Themammalian fauna indicates a medial Blancanage (3.6–2.7 Ma) for the Arroyo de la ParidaLF. No other geochronologic data are cur-rently available for Arroyo de la Parida. Oth-er faunas from the Palomas Formation far-ther south in the Engle and Palomas basinsare either early or medial Blancan.

The Hatch LF from the Camp Rice For-mation in the Hatch-Rincon basin sharesGeomys (Nerterogeomys) paenebursariuswith the Pajarito and Belen faunas. A medial


Blancan age is further indicated by the lackof South American immigrants and the fau-nal and stratigraphic similarity to the TonucoMountain LF (Morgan et al., 1998). A mag-netostratigraphic section in the Camp RiceFormation at nearby Hatch Siphon (Mack etal., 1993) does not cross the Gilbert/Gaussboundary but samples most of the GaussChron, including both the Kaena and Mam-moth Subchrons, and is thus between 3.6 and2.6 Ma. The Hatch Siphon section is similarto the Cedar Hill magnetostratigraphic sec-tion (Mack et al., 1993) that contains theTonuco Mountain LF (Morgan et al., 1998),further supporting a medial Blancan age forthe Hatch LF (between 3.6 and 2.7 Ma).

The Tonuco Mountain LF from the CampRice Formation in the Jornada basin has sixspecies of mammals that are indicative of theBlancan: Canis lepophagus, Borophagus sp.,Nannippus peninsulatus, Equus simplicidens,Platygonus cf. P. bicalcaratus, and Hem-iauchenia blancoensis. E. simplicidens is ab-sent from very early Blancan faunas, Ca-melops and E. scotti appear in the medialBlancan, and most Blancan records of Nan-nippus predate the Gauss/Matuyama magnet-ic reversal at 2.6 Ma. The absence of SouthAmerican mammals suggests the fauna isolder than 2.7 Ma. The biostratigraphic datarestrict the age of the Tonuco Mountain LFto medial Blancan. A magnetostratigraphicsection in the Camp Rice Formation at CedarHill (Mack et al., 1993) can be directly cor-related with the Tonuco Mountain LF. TheCedar Hill section is entirely within theGauss Chron, and the fossiliferous interval isbelow the top of the Kaena Subchron (olderthan 3.0 Ma). Biostratigraphic and magne-tostratigraphic data constrain the age of theTonuco Mountain LF to the early medialBlancan (3.6–3.0 Ma).

About 10 sites in New Mexico of medialBlancan age (3.6–2.7 Ma) are among theleast well constrained by biostratigraphy inthe state. Many medial Blancan sites areidentified primarily by lack of characteristicearly or late Blancan taxa, rather than by thepresence of taxa that are diagnostic of themedial Blancan. Lindsay et al. (1984) listeda number of genera whose first appearanceat about 3.7 Ma defines the beginning ofwhat we recognize as the medial Blancan.

However, many of these taxa are either un-known from New Mexican Blancan faunas(e.g., Chasmaporthetes, Trigonicitis, Ursus)or also occur in early Blancan faunas (e.g.,Neotoma, Platygonus). Furthermore, no me-dial Blancan fauna currently known fromNew Mexico has a rich microvertebrate sam-ple, although several sites do contain smallmammals, including Geomys (Nerterogeo-mys) paenebursarius from Pajarito, Belen,and Hatch, Scalopus (Hesperoscalops) blan-coensis from Belen, and Geomys (Geomys)sp. and Sigmodon medius from PalomasCreek. A medial Blancan age can be firmlyestablished for the Pajarito, Hatch, and Ton-uco Moutain faunas from associated geo-chronologic data. Pumice Ar/Ar dated at 3.12Ma (Maldonado et al., 1999) is in direct as-sociation with the Pajarito LF. An Ar/Ar dateof exactly the same age (3.12 Ma) on a pum-ice-clast conglomerate from Hatch Siphon(Mack et al., 1998) can be correlated withthe Hatch LF. A magnetostratigraphic sectionfrom Hatch Siphon (Mack et al., 1998) canbe correlated with the Gauss Chron (3.58–2.58 Ma). A magnetostratigraphic sectionfrom Cedar Hill (Mack et al., 1993) can bedirectly correlated with the Tonuco MountainLF and indicates an age between 3.58 and3.04 Ma.

Because the medial Blancan is difficult tocharacterize biostratigraphically, an argu-ment could be made that it should be includ-ed in the early Blancan (e.g., Lundelius etal., 1987; Woodburne and Swisher, 1995).Careful study of early Blancan (e.g., WhiteBluffs) and medial Blancan (e.g., Hagerman)faunas that have extensive samples of bothlarge and small mammals, as well as asso-ciated magnetostratigraphy and radioisotopicdates, should help to clarify the faunal andtime relationships between these two inter-vals. The best solution might be to recognizeRepenning’s five Blancan microtine zones(Blancan I–V) as subdivisions of the Blancanthat are defined by their faunas of both mi-crotine rodents and other mammals. For nowwe recognize a medial Blancan interval thatcorresponds with the Gauss Chron (3.58–2.58 Ma), with the exception that the upperboundary is defined by the first appearanceof Neotropical immigrant mammals at about2.7 Ma, slightly before the end of the Gauss.


Five faunas from New Mexico are lateBlancan in age (2.7–1.8 Ma): Santo Domin-go, Mesilla Basin Faunas A and B, PearsonMesa, and Virden. Late Blancan faunas arerecognized by the first appearance of Neo-tropical immigrant mammals at about 2.7Ma. With the exception of Santo Domingo,the remaining four late Blancan faunas fromNew Mexico have one or more taxa of Neo-tropical immigrants. Repenning (1987) alsonoted several first appearances of Eurasianmicrotine rodents at about this same time(Blancan V), including the lemming generaMictomys and Synaptomys. Microtine rodentsare unknown from New Mexican late Blan-can faunas. The five late Blancan faunasfrom New Mexico appear to separate intotwo groups, three faunas (Santo Domingo,Mesilla A, and Pearson Mesa) that containNannippus, and are thus older than 2.2 Ma(early late Blancan, 2.7–2.2 Ma), and twofaunas (Mesilla B and Virden) that lack Nan-nippus, and thus appear to be younger (latestBlancan, 2.2–1.8 Ma).

The Santo Domingo LF from the SierraLadrones Formation in the Albuquerque ba-sin has four species of mammals, none ofwhich are definitively late Blancan. The pres-ence of Nannippus peninsulatus suggests thefauna is older than 2.2 Ma, whereas Equuscalobatus and E. scotti occur in medial Blan-can through early Irvingtonian faunas. Ac-cording to Tedford (1981), the strata that pro-duced the Santo Domingo LF are interbed-ded with the Santa Ana Mesa basalts, K/Ardated at 2.67 and 2.41 Ma (Smith and Kuhle,1998), and are overlain by the lower Ban-delier Tuff, Ar/Ar dated at 1.61 Ma (Izett andObradovich, 1994). The combination of bio-stratigraphy and radioisotopic dates con-strains the age of the Santo Domingo LF be-tween 2.7 and 2.2 Ma.

Mesilla Basin Fauna A from the CampRice Formation in southernmost New Mex-ico (Vanderhill, 1986) and the Pearson MesaLF from the Gila Group in southwesternNew Mexico (Morgan and Lucas, 2000b) aresimilar in age. The association of Glyptothe-rium with Nannippus in the Mesilla A faunaclearly establishes a late Blancan age, as theonly interval during which these two generacoexisted in southwestern faunas was be-tween 2.7 Ma (the beginning of the Great

American Faunal Interchange) and 2.2 Ma(the Nannippus extinction datum of Lindsayet al., 1984). Magnetostratigraphic data forMesilla A indicate correlation with the upperGauss Chron (Vanderhill, 1986), restrictingthe age of this fauna to older than 2.58 Ma.

The Pearson Mesa LF also documents theassociation of Nannippus with a Neotropicalimmigrant, the mylodont ground sloth Glos-sotherium chapadmalense. The first appear-ance of Glossotherium and Glyptotherium, aswell as several other Neotropical immigrantsdiscussed below, identifies the onset of theGreat American Interchange at about 2.7 Ma,and defines the beginning of the late Blan-can. A magnetostratigraphic section fromPearson Mesa (Tomida, 1987) further re-stricts the age of the lower portion of thesection, including the Pearson Mesa LF, tothe upper Gauss Chron (3.0–2.6 Ma). Bio-stratigraphy and magnetostratigraphy forPearson Mesa and Mesilla A seem to tightlyconstrain the ages of these faunas between2.7 Ma (earliest appearance of Neotropicalimmigrants) and 2.6 Ma (Gauss/Matuyamaboundary).

The exact timing of the onset of the GreatAmerican Interchange in North America hasnot been firmly established, although it iswell documented that the first appearance ofSouth American immigrants in the south-western United States occurred in the upperGauss Chron, sometime between the top ofthe Kaena Subchron (3.04 Ma) and theGauss/Matuyama boundary (2.58 Ma). Sixlate Blancan sites in the southwestern UnitedStates record the first appearance of SouthAmerican mammals in the upper GaussChron: 111 Ranch (Galusha et al., 1984) andWolf Ranch (Harrison, 1978) in Arizona,Pearson Mesa (Tomida, 1987; Morgan andLucas, 2000b) and Mesilla Basin Fauna A(Vanderhill, 1986) in New Mexico, and CitaCanyon (Lindsay et al., 1976) and Hudspeth(Strain, 1966; Vanderhill, 1986) in Texas. At111 Ranch, the best documented of these sixfaunas (Galusha et al., 1984), Neotropicalmammals appear in the uppermost Gauss,and thus the date of 2.7 Ma has often beencited as the first appearance datum for Neo-tropical immigrants in North America (e.g.,Woodburne and Swisher, 1995), as well asthe boundary between the early and late


Blancan (or medial and late Blancan as usedhere). The first appearance datum for twogenera of Neotropical xenarthrans (Glypto-therium and Glossotherium) and two generaof Neotropical caviomorph rodents (Neocho-erus and Erethizon) is within the upperGauss Chron, including: Glossotherium atPearson Mesa and Cita Canyon; Glyptothe-rium at Cita Canyon, Hudspeth, Mesilla A,and 111 Ranch; the capybara Neochoerus at111 Ranch; and the porcupine Erethizon atWolf Ranch. Several other sites documentthe occurrence of Neotropical immigrants inthe early Matuyama Chron (2.6–2.2 Ma), in-cluding the Blanco LF in Texas (Dalquest,1975; Lindsay et al., 1976, 1984) and theAnza-Borrego Desert in California (Opdykeet al., 1977; Cassiliano, 1999). Two addition-al genera of Neotropical xenarthrans, the ar-madillo Dasypus and the pamapthere Hol-mesina, as well as Glossotherium and Neo-choerus, occur in the early Matuyama Chronin the Macasphalt Shell Pit LF in southernFlorida (Morgan and Ridgway, 1987; Joneset al., 1991; Morgan and Hulbert, 1995). Noearly or medial Blancan (4.5–2.7 Ma) sitesnorth of Mexico are known to contain Neo-tropical mammals involved in the GreatAmerican Interchange. However, several fau-nas from central Mexico suggest that the ini-tial migration of South American mammalsacross the Panamanian Isthmus may have oc-curred as early as 4.7 Ma (Miller and Car-ranza-Castaneda, 2001, 2002). We use 2.7Ma for the beginning of the Interchange inthe southwestern United States, with the un-derstanding that detailed stratigraphic andgeochronologic studies of sites in centralMexico may eventually push back the rec-ognized age of onset of Interchange in trop-ical North America.

Mesilla B and the Virden LF occur higherin the same stratigraphic sequences as theMesilla A and Pearson Mesa faunas, respec-tively. The Mesilla B mammalian fauna con-tains three taxa restricted to the Blancan, thelarge camelids Blancocamelus, Gigantoca-melus, and an undescribed Camelops. Othertypical Blancan genera such as Nannippusare absent from Mesilla B, suggesting thefauna is younger than 2.2 Ma. The rabbit Al-uralagus virginiae, identified from Mesilla B(Vanderhill, 1986), is known elsewhere only

from Blancan/Irvingtonian transitional fau-nas, including Curtis Ranch and San SimonPower Line in southern Arizona (Tomida,1987). Three other species from Mesilla B,Glyptotherium arizonae, Smilodon gracilis,and Tapirus haysii, are more typical of earlyIrvingtonian faunas, but are also known fromthe late Blancan. The type locality of G. ar-izonae, Curtis Ranch in Arizona, althoughconsidered early Irvingtonian by most work-ers (e.g., Lundelius et al., 1987; Repenning,1987), has more recently been placed in thelatest Blancan (Lindsay et al., 1990). Thereare also five late Blancan records of thisglyptodont from Florida (Morgan and Hul-bert, 1995). Likewise, most records of S.gracilis are from the early Irvingtonian, butthis small sabercat is also known from sev-eral Florida late Blancan faunas (Berta,1987). T. haysii occurs in late Blancan faunasin Texas and Colorado (Strain, 1966; Hager,1974; Hulbert, 1995). Mammuthus is absentfrom Mesilla B, but appears higher in thesame stratigraphic sequence in Mesilla C.Magnetostratigraphic data for Mesilla B(Vanderhill, 1986) place this fauna in thetime interval between the Gauss/Matuyamaboundary and the Olduvai Subchron (2.6–1.8Ma). Biostratigraphic evidence indicates thatMesilla B belongs in the younger half of thisinterval (2.2–1.8 Ma).

The Virden LF from the Duncan basin inthe Gila River Valley has Glyptotherium ar-izonae but lacks Nannippus, indicating thatthis fauna is younger than the Pearson MesaLF, derived from Gila Group strata about 45m lower in the same section. Although glyp-todonts first appear in southwestern faunas inthe early late Blancan (about 2.7 Ma), theseearly occurrences represent the smaller spe-cies G. texanum. As discussed above, G. ar-izonae is now known from both latest Blan-can and early Irvingtonian faunas in thesouthwest, as well as late Blancan and earlyIrvingtonian faunas in Florida (Morgan andHulbert, 1995). Canis lepophagus from Vir-den is restricted to the Blancan, and occursin the late Blancan Cita Canyon and RedLight faunas in Texas (Akersten, 1972) andthe late Blancan 111 Ranch in Arizona (Gal-usha et al., 1984; Tomida, 1987). The pres-ence of C. lepophagus strongly indicates aBlancan age for the Virden LF, while the


presence of G. arizonae further suggests thatthe fauna is very late Blancan.

Mesilla B and Virden appear to be similarin age based on the occurrence of the largeGlyptotherium arizonae and the absence ofNannippus and Mammuthus. Taxa restrictedto the Blancan are known from each fauna,including Blancocamelus and Gigantocame-lus from Mesilla B and Canis lepophagusfrom Virden. Nannippus does occur in lowerstratigraphic units in both the Mesilla Basinand Pearson Mesa sections, suggesting thatthe Mesilla B and Virden faunas are youngerthan the Nannippus extinction datum at 2.2Ma. Mammuthus is absent from Mesilla B,but occurs higher in the same stratigraphicsequence in the Mesilla C fauna. Biostratig-raphy, magnetostratigraphy, and radioisoto-pic dates constrain the age of Mesilla B tothe latest Blancan (2.2–1.8 Ma). Biostrati-graphic correlation indicates that the VirdenLF belongs in this age range as well.

Three early Irvingtonian faunas from NewMexico contain more than five species ofmammals: Tijeras Arroyo, Tortugas Moun-tain, and Mesilla Basin Fauna C (figs. 12.2–12.4; table 12.2). Mammuthus, whose firstappearance defines the beginning of the Ir-vingtonian (Lundelius et al., 1987), is knownfrom all three of theses faunas. The co-oc-currence in the Tijeras Arroyo fauna of Glyp-totherium arizonae, Equus scotti, and Mam-muthus is typical of southwestern early Ir-vingtonian faunas (1.6–1.0 Ma), includingGilliland in Texas (Hibbard and Dalquest,1966) and Holloman in Oklahoma (Dalquest,1977). Mandibles of Mammuthus meridion-alis from Tijeras Arroyo represent one of themost primitive mammoths known fromNorth America (Lucas and Effinger, 1991;Lucas et al., 1993). This specimen is also oneof the oldest well-documented records ofMammuthus from North America (Lucas,1995, 1996), based on its association withpumice derived from the lower Bandelier tuff(Lucas et al., 1993). The lower Bandelier tuffhas an Ar/Ar date of 1.61 Ma (Izett and Ob-radovich, 1994). Although this date providesa maximum age for the Tijeras Arroyo mam-moth, similar ages on pumice deposits farthersouth in the Rio Grande Valley, including thesouthern Mesilla basin (Mack et al., 1996,1998), suggest that deposition of widespread

fluvially transported pumice beds at about1.6 Ma was essentially synchronous with theformation of the lower Bandelier tuff in theJemez volcanic field in northern New Mex-ico.

The Tortugas Mountain LF from the north-ern Mesilla basin (Lucas et al., 1999, 2000)contains three proboscideans, Cuvieroniustropicus, Stegomastodon mirificus, and Mam-muthus imperator. Mammuthus arrived fromEurasia in the early Pleistocene about 1.6Ma. The youngest well-dated record of Ste-gomastodon is from Tule Canyon in the Tex-as Panhandle, where it is associated withMammuthus in a volcanic ash at the base ofthe Tule Formation dated between 1.3 and1.2 Ma (Izett, 1977; Tedford, 1981; Madden,1983). Thus, the co-occurrence of Stegomas-todon and Mammuthus defines a restrictedinterval of time in the early Irvingtonian, be-tween about 1.6 and 1.2 Ma, after the arrivalof Mammuthus and before the extinction ofStegomastodon. The Tortugas Mountain LFis similar in age to the Gilliland LF in Texas,which is the only other fauna that documentsthe association of Cuvieronius, Stegomasto-don, and Mammuthus (Hibbard and Da-lquest, 1966).

Among New Mexico’s early Irvingtonianfaunas, Mesilla C in the southern Mesilla ba-sin has the most diverse sample of largemammals (Vanderhill, 1986). Three speciesfrom Mesilla C clearly establish an Irving-tonian age, Mammuthus cf. M. meridionalis,the wolflike Canis armbrusteri, and the bea-ver Castor canadensis. The primitive mam-moth M. meridionalis occurs only in earlyIrvingtonian faunas, C. armbrusteri first ap-pears in the early Irvingtonian and becomesextinct in the late Irvingtonian (Berta, 1995),and the extant C. canadensis is limited toIrvingtonian and younger faunas. The Mesi-lla C fauna is very similar to early Irving-tonian faunas from the southern Great Plains,including Gilliland and Rock Creek in Texas(Hibbard and Dalquest, 1966) and Hollomanin Oklahoma (Dalquest, 1977), that docu-ment the association of Glyptotherium ari-zonae, Paramylodon harlani, Equus scotti,E. calobatus, and Mammuthus. The magne-tostratigraphy of Mesilla C (Vanderhill,1986) suggests correlation with the intervalin the Matuyama Chron from just after the


Olduvai Subchron (1.81 Ma) until just priorto the Jaramillo Subchron (1.07 Ma). Ar/Ardates of 1.59 Ma and 1.32 Ma on pumicebeds from the Camp Rice Formation near LaUnion agree, suggesting an age between 1.6and 1.1 Ma for Mesilla C (Vanderhill, 1986;Mack et al., 1996).

We recognize the beginning of the Irving-tonian based on the first appearance of Mam-muthus in the early Pleistocene between 1.8and 1.6 Ma. Cassiliano (1999) could not pre-cisely determine the position of the Blancan/Irvingtonian boundary, suggesting an agerange between 2.15 Ma and 1.95 Ma (latestPliocene). He analyzed the utility of severalgenera to define the Blancan/Irvingtonianboundary (e.g., Mammuthus, Smilodon, Le-pus), and found none of these genera to beappropriate. One of the most difficult prob-lems encountered by Cassiliano (1999) wasthat Mammuthus, the most frequently citedgenus for defining the beginning of the Ir-vingtonian, is absent from the two most com-plete stratigraphic sequences in North Amer-ica that span the Blancan/Irvingtonianboundary, the San Pedro Valley in Arizona(Johnson et al., 1975; Lindsay et al., 1990)and the Anza-Borrego Desert (also known asthe Fish Creek-Vallecito Creek section) insouthern California (Opdyke et al., 1977;Cassiliano, 1999).

Two stratigraphic sequences from NewMexico, Tijeras Arroyo and the southernMesilla Basin, contain early Irvingtonianfaunas with Mammuthus superposed aboveBlancan faunas. Mammuthus fossils from Ti-jeras Arroyo and Mesilla C, referred to M.meridionalis, are among the oldest datedmammoths in North America, as both areclosely associated with radioisotopic dates of1.6 Ma on pumice from the lower Bandeliertuff. Mammoths from Wellsch Valley, Sas-katchewan (Barendregt et al., 1991) andThornton Beach, California (Madden, 1980,1995) were thought to be older than 1.5 Ma,but both sites are now known to be consid-erably younger (Barendregt et al., 1991; Lu-cas, 1995, 1996; Cassiliano, 1999). All otherearly Irvingtonian records of Mammuthus areyounger than 1.5 Ma.

The southern Mesilla Basin may possessone of the most important stratigraphic se-quences in North America for determining

the first appearance of Mammuthus and theplacement of the Blancan/Irvingtonianboundary. Mammuthus occurs in a fairlycomplete stratigraphic sequence that spansthe late Blancan and early Irvingtonian. Thestratigraphic sequence of the Camp Rice For-mation in the vicinity of La Union andChamberino in the southern Mesilla Basincontains two diverse superposed mammalianfaunas, the latest Blancan Mesilla B and ear-ly Irvingtonian Mesilla C, as well as the lateBlancan Mesilla A at the base of the sectionthat documents the association of Nannippusand Glyptotherium. Further study of this im-portant sequence is ongoing, and will includedetailed correlation of magnetostratigraphy(Vanderhill, 1986), radioisotopic dates (Macket al., 1996), lithostratigraphy, and biostratig-raphy.

The youngest Irvingtonian fauna in NewMexico is San Antonio Mountain (SAM)Cave from the San Luis basin near the Col-orado border. Magnetostratigraphy and mi-crotine rodent biochronology constrain theage of the SAM Cave fauna to the medialIrvingtonian; however, SAM Cave containsnine individual sites with a range of ages be-tween about 1.0 and 0.7 Ma (Rogers et al.,2000). The four oldest sites in SAM Cavecontain the microtines Mictomys kansasensis,an advanced species of Allophaiomys, Lem-miscus curtatus, and Microtus cf. M. califor-nicus, indicating ages between about 1.0 and0.85 Ma, in the early part of the medial Ir-vingtonian. A slightly younger medial Ir-vingtonian site in SAM Cave contains Cleth-rionomys, and is between 0.85 and 0.78 Main age. The occurrences of Lemmiscus andClethrionomys in SAM Cave represent theoldest records of these two genera in NorthAmerica.

ACKNOWLEDGMENTS

We are particularly grateful to RichardTedford for his help and encouragement dur-ing our project to collect and describe NewMexico’s Blancan and Irvingtonian faunas.Our original motivation for this undertakingcame from Dr. Tedford’s 1981 paper on themammalian biochronology of the late Ce-nozoic basins of New Mexico. Before his pa-per, the Pliocene and early Pleistocene ver-


tebrate record of New Mexico had been vir-tually ignored. We thank Greg McDonald forreviewing several of our previous papers andfor sharing with us his comprehensiveknowledge of North American Blancan fau-nas. Greg McDonald, Nicholas Czaplewski,and Lawrence Flynn provided helpful com-ments on this paper. Numerous people haveassisted us in the field collecting Blancan andIrvingtonian fossils in New Mexico, espe-cially Paul Sealey, Warren Slade, and JerryMacDonald, and also including the late JohnEstep, Ed Frye, Jerald Harris, Paul Knight,Peter Kondrashov, Thomas Logan, WayneOakes, Mike O’Keefe, Mike O’Neill, PeteReser, Jay Sobus, Christopher Whittle, Bren-da Wilkinson, and Bill Wood. Collectors forthe Frick Laboratory who worked on Blan-can and Irvingtonian sites in New Mexicoinclude Charles Falkenbach, Ted Galusha,George Pearce, and Joseph Rak. The NewMexico collections of the Frick Laboratory,housed at the American Museum of NaturalHistory, formed the basis for Tedford’s 1981paper, and also paved the way for all futurestudies of New Mexico’s Neogene vertebratefauna. Geologists who have assisted us in ourstratigraphic studies, several of whom havecollected significant fossils, include StevenCather, Sean Connell, John Hawley, PatriciaJackson-Paul, Daniel Koning, David Love,Greg Mack, and Florian Maldonado.

REFERENCES

Akersten, W.A. 1972. Red Light local fauna(Blancan) of the Love Formation, southeasternHudspeth County, Texas. Texas Memorial Mu-seum Bulletin 20: 1–53.

Bachman, G.O., and H.H. Mehnert. 1978. New K-Ar dates and the late Pliocene to Holocene geo-morphic history of the central Rio Grande re-gion, New Mexico. Geological Society ofAmerica Bulletin 89: 283–292.

Barendregt, R.W., F.F. Thomas, E. Irving, J. Baker,A. MacS. Stalker, and C.S. Churcher. 1991.Stratigraphy and paleomagnetism of the JawFace section, Wellsch Valley site, Saskatche-wan. Canadian Journal of Earth Science 28:1353–1364.

Berggren, W.A., F.J. Hilgen, C.G. Langereis, D.V.Kent, J.D. Obradovich, I. Raffi, M.E. Raymo,and N.J. Shackleton. 1995. Late Neogene chro-nology: new perspectives in high-resolutionstratigraphy. Geological Society of AmericaBulletin 107: 1272–1287.

Berta, A. 1987. The sabercat Smilodon gracilisfrom Florida and a discussion of its relation-ships (Mammalia, Felidae, Smilodontini). Bul-letin of the Florida State Museum, BiologicalScience 31(1): 1–63.

Berta, A. 1995. Fossil carnivores from the LeiseyShell Pits, Hillsborough County, Florida. InR.C. Hulbert, Jr., G.S. Morgan, and S.D. Webb(editors), Paleontology and geology of the Leis-ey Shell Pits, early Pleistocene of Florida. Bul-letin of the Florida Museum of Natural History37, Pt. II: 463–499.

Cassiliano, M.L. 1999. Biostratigraphy of Blancanand Irvingtonian mammals in the Fish Creek–Vallecito Creek section, southern California,and a review of the Blancan-Irvingtonianboundary. Journal of Vertebrate Paleontology19: 169–186.

Connell, S.D., D.J. Koning, and S.M. Cather.1999. Revisions to the stratigraphic nomencla-ture of the Santa Fe Group, northwestern Al-buquerque Basin, New Mexico. New MexicoGeological Society Guidebook 50: 337–353.

Czaplewski, N.J. 1987. Sigmodont rodents (Mam-malia: Muroidea: Sigmodontinae) from the Pli-ocene (early Blancan) Verde Formation, Ari-zona. Journal of Vertebrate Paleontology 7:183–199.

Czaplewski, N.J. 1990. The Verde local fauna:small vertebrate fossils from the Verde For-mation, Arizona. San Bernardino County Mu-seum Association Quarterly 37(3): 1–39.

Dalquest, W.W. 1975. Vertebrate fossils from theBlanco local fauna of Texas. Occasional Pa-pers, The Museum, Texas Tech University 30:1–52.

Dalquest, W.W. 1977. Mammals of the Hollomanlocal fauna, Pleistocene of Oklahoma. South-western Naturalist 22: 255–268.

Dalquest, W.W. 1978. Early Blancan mammals ofthe Beck Ranch local fauna of Texas. Journalof Mammalogy 59: 269–298.

DeBrine, B., Z. Spiegel, and D. William. 1963.Cenozoic sedimentary rocks in Socorro Valley,New Mexico. New Mexico Geological SocietyGuidebook 14: 123–131.

Denny, C.S. 1940. Tertiary geology of the SanAcacia area, New Mexico. Journal of Geology48: 73–106.

Eshelman, R.E. 1975. Geology and paleontologyof the early Pleistocene (late Blancan) WhiteRock fauna from north-central Kansas. Studieson Cenozoic paleontology and stratigraphy,Claude W. Hibbard Memorial Volume 4. Uni-versity of Michigan Papers on Paleontology 13:1–60.

Frick, C. 1933. New remains of trilophodont-te-trabelodont mastodons. Bulletin of the Ameri-can Museum of Natural History 59: 505–652.

Galusha, T., N.M. Johnson, E.H. Lindsay, N.D.


Opdyke, and R.H. Tedford. 1984. Biostratigra-phy and magnetostratigraphy, late Pliocenerocks, 111 Ranch, Arizona. Geological Societyof America Bulletin 95: 714–722.

Gillette, D.D., and C.E. Ray. 1981. Glyptodontsof North America. Smithsonian Contributionsto Paleobiology 40: 1–255.

Goodwin, H.T. 1995. Systematic revision of fossilprairie dogs with descriptions of two new spe-cies. University of Kansas Natural History Mu-seum Miscellaneous Publications 86: 1–38.

Gustafson, E.P. 1978. The vertebrate faunas of thePliocene Ringold Formation, south-centralWashington. Bulletin of the Museum of NaturalHistory, University of Oregon 23: 1–62.

Gustafson, E.P. 1985. Soricids (Mammalia, Insec-tivora) from the Blufftop local fauna, BlancanRingold Formation of central Washington, andthe correlation of Ringold Formation faunas.Journal of Vertebrate Paleontology 5: 88–92.

Hager, M.W. 1974. Late Pliocene and Pleistocenehistory of the Donnelly Ranch vertebrate site,southeastern Colorado. University of WyomingContributions to Geology, Special Paper 2: 1–62.

Harris, A.H., and L.S.W. Porter. 1980. Late Pleis-tocene horses of Dry Cave, Eddy County, NewMexico. Journal of Mammalogy 61: 46–65.

Harrison, J.A. 1978. Mammals of the Wolf Ranchlocal fauna, Pliocene of the San Pedro Valley,Arizona. Occasional Papers of the Museum ofNatural History, University of Kansas 73: 1–18.

Hawley, J.W. 1978. Guidebook to Rio Grande riftin New Mexico and Colorado. New MexicoBureau of Mines and Mineral Resources Cir-cular 163: 1–241.

Hawley, J.W., F.E. Kottlowski, W.R. Seager, W.E.King, W.S. Strain, and D.V. LeMone. 1969. TheSanta Fe Group in the south-central New Mex-ico border region. New Mexico Bureau ofMines and Mineral Resources Circular 104:52–76.

Hibbard, C.W. 1938. An upper Pliocene faunafrom Meade County, Kansas. Kansas Academyof Science, Transactions 40: 239–265.

Hibbard, C.W. 1939. Four new rabbits from theupper Pliocene of Kansas. American MidlandNaturalist 21: 506–513.

Hibbard, C.W. 1941. New mammals from theRexroad fauna, upper Pliocene of Kansas.American Midland Naturalist 26: 337–368.

Hibbard, C.W. 1950. Mammals of the RexroadFormation from Fox Canyon, Kansas. Contri-butions from the Museum of Paleontology,University of Michigan 8(6): 113–192.

Hibbard, C.W. 1953. The insectivores of the Rex-road fauna, upper Pliocene of Kansas. Journalof Paleontology 27: 21–32.

Hibbard, C.W. 1967. New rodents from the Late

Cenozoic of Kansas. Papers of the MichiganAcademy of Science, Arts, and Letters 52:115–131.

Hibbard, C.W., and W.W. Dalquest. 1966. Fossilsfrom the Seymour Formation of Knox and Bay-lor counties, Texas, and their bearing on the lateKansan climate of that region. Contributions tothe Museum of Paleontology, University ofMichigan 21(1): 1–66.

Hulbert, R.C., Jr. 1995. The giant tapir, Tapirushaysii, from Leisey Shell Pit 1A and other Flor-ida Irvingtonian localities. In R.C. Hulbert, Jr.,G.S. Morgan, and S.D. Webb (editors), Pale-ontology and geology of the Leisey Shell Pits,early Pleistocene of Florida. Bulletin of theFlorida Museum of Natural History 37, Pt. II:515–551.

Izett, G.A. 1977. Volcanic ash beds in continentaldeposits of the Southern High Plains: Theirbearing on the time of the Blancan-Irvingtonianfaunal transition. Geological Society of Amer-ica Abstracts with Programs 9: 1034.

Izett, G.A., and J.D. Obradovich. 1994. 40Ar/39Arage constraints for the Jaramillo Normal Sub-chron and the Matuyama-Brunhes geomagneticboundary. Journal of Geophysical Research99(B2): 2925–2934.

Izett, G.A., J.D. Obradovich, C.W. Naeser, andG.T. Cebula. 1981. Potassium-argon and fissiontrack zircon ages of Cerro Toledo rhyolite teph-ra in the Jemez Mountains, New Mexico. U.S.Geological Survey Professional Paper 1199-D:37–43.

Johnson, N.M., N.P. Opdyke, and E.H. Lindsay.1975. Magnetic polarity stratigraphy of Plio-cene-Pleistocene terrestrial deposits and verte-brate faunas, San Pedro Valley, Arizona. Geo-logical Society of America Bulletin 86: 5–12.

Jones, D.S., B.J. MacFadden, S.D. Webb, P.A.Mueller, D.A. Hodell, and T.M. Cronin. 1991.Integrated geochronology of a classic Pliocenefossil site in Florida: linking marine and terres-trial biochronologies. Journal of Geology 99:637–648.

Knight, P.J., S.G. Lucas, and A. Cully. 1996. Ear-ly Pleistocene (Irvingtonian) plants from theAlbuquerque area, New Mexico. SouthwesternNaturalist 41: 207–217.

Koning, D.J., S.D. Connell, F.J. Pazzaglia, andW.C. McIntosh. 2001. Stratigraphy of the Tuer-to and Ancha Formations (Upper Santa FeGroup), Hagan and Santa Fe embayments,north-central New Mexico. New Mexico Bu-reau of Mines and Mineral Resources, Open-File Report 454A:I-1-I-10.

Kurten, B., and E. Anderson. 1980. The Pleisto-cene mammals of North America. New York:Columbia University Press.

Lance, J.F. 1950. Paleontologıa y estratigraphiadel Plioceno de Yepomera, estado de Chihua-


hua-1a parte: equidos, excepto Neohipparion.Universidad Nacional Autonoma de Mexico,Instituto de Geologıa, Boletin Numero 54: 1–81.

Lindsay, E.H., and L.L. Jacobs. 1985. Pliocenesmall mammal fossils from Chihuahua, Mexi-co. Universidad Nacional Autonoma de Mexi-co, Instituto de Geologıa, Paleontologıa Mexi-cana Numero 51: 1–53.

Lindsay, E.H., N.M. Johnson, and N.D. Opdyke.1976. Preliminary correlation of North Ameri-can land mammal ages and geomagnetic chro-nology. University of Michigan Papers on Pa-leontology 12: 111–119.

Lindsay, E.H., N.D. Opdyke, and N.M. Johnson.1984. Blancan-Hemphillian land mammal agesand late Cenozoic mammal dispersal events.Annual Review of Earth and Planetary Scienc-es 12: 445–488.

Lindsay, E.H., G.S. Smith, C.V. Haynes, and N.D.Opdyke. 1990. Sediments, geomorphology,magnetostratigraphy, and vertebrate paleontol-ogy in the San Pedro Valley, Arizona. Journalof Geology 98: 605–619.

Lozinsky, R.P. 1986. Geology and late Cenozoichistory of the Elephant Butte area, Sierra Coun-ty, New Mexico. New Mexico Bureau of Minesand Mineral Resources Circular 187: 1–40.

Lozinsky, R.P., and R.H. Tedford. 1991. Geologyand paleontology of the Santa Fe Group, south-western Albuquerque basin, Valencia County,New Mexico. New Mexico Bureau of Minesand Mineral Resources Circular 132: 1–35.

Lucas, S.G. 1995. The Thornton Beach mammothand the antiquity of Mammuthus in NorthAmerica. Quaternary Research 43: 263–264.

Lucas, S.G. 1996. The Thornton Beach mam-moth: consistency of numerical age and mor-phology. Quaternary Research 45: 332–333.

Lucas, S.G., and J.E. Effinger. 1991. Mammuthusfrom Lincoln County and a review of the mam-moths from the Pleistocene of New Mexico.New Mexico Geological Society Guidebook42: 277–282.

Lucas, S.G., A.B. Heckert, and P.L. Sealey. 1995.A fossil specimen of the long-nosed snakeRhinocheilus from the Pliocene of southernNew Mexico. Texas Journal of Science 47: 9–12.

Lucas, S.G., and G.S. Morgan. 1996. The Plio-cene proboscidean Rhynchotherium (Mamma-lia: Gomphotheriidae) from south-central NewMexico. Texas Journal of Science 48: 311–318.

Lucas, S.G., and G.S. Morgan. 1999. The oldestMammut (Mammalia: Proboscidea) from NewMexico. New Mexico Geology 21(1): 10–12.

Lucas, S.G., G.S. Morgan, and J.W. Estep. 2000.Biochronological significance of the co-occur-rence of the proboscideans Cuvieronius, Ste-gomastodon, and Mammuthus in the lower

Pleistocene of southern New Mexico. NewMexico’s Fossil Record 2, New Mexico Mu-seum of Natural History Science Bulletin 16:209–216.

Lucas, S.G., G.S. Morgan, J.W. Estep, G.H.Mack, and J.W. Hawley. 1999. Co-occurrenceof the proboscideans Cuvieronius, Stegomas-todon, and Mammuthus in the lower Pleisto-cene of southern New Mexico. Journal of Ver-tebrate Paleontology 19(3): 595–597.

Lucas, S.G., and W. Oakes. 1986. Pliocene (Blan-can) vertebrates from the Palomas Formation,south-central New Mexico. New Mexico Geo-logical Society Guidebook 37: 249–255.

Lucas, S.G., T.E. Williamson, and J. Sobus. 1993.Plio-Pleistocene stratigraphy, paleoecology,and mammalian biochronology, Tijeras Arroyo,Albuquerque area, New Mexico. New MexicoGeology 15: 1–8.

Lundelius, E.L., Jr., C.S. Churcher, T. Downs,C.R. Harington, E.H. Lindsay, G.E. Schultz,H.A. Semken, S.D. Webb, and R.J. Zakrzewski.1987. The North American Quaternary se-quence. In M.O. Woodburne (editor), Cenozoicmammals of North America: geochronologyand biostratigraphy: 211–235. Berkeley: Uni-versity of California Press.

MacFadden, B.J. 1977. Magnetic polarity stratig-raphy of the Chamita Formation stratotype(Mio-Pliocene) of north-central New Mexico.American Journal of Science 277: 769–800.

MacFadden, B.J. 1984. Astrohippus and Dinohip-pus from the Yepomera local fauna (Hemphil-lian, Mexico) and implications for the phylog-eny of one-toed horses. Journal of VertebratePaleontology 4: 273–283.

MacFadden, B.J., and H. Galiano. 1981. LateHemphillian cat (Mammalia, Felidae) from theBone Valley Formation of central Florida. Jour-nal of Paleontology 55: 218–226.

Mack, G.H., W.C. McIntosh, M.R. Leeder, andH.C. Monger. 1996. Plio-Pleistocene pumicefloods in the ancestral Rio Grande, southernRio Grande rift, USA. Sedimentary Geology103: 1–8.

Mack, G.H., S.L. Salyards, and W.C. James. 1993.Magnetostratigraphy of the Plio-PleistoceneCamp Rice and Palomas Formation in the RioGrande rift of southern New Mexico. AmericanJournal of Science 293: 49–77.

Mack, G.H., S.L. Salyards, W.C. McIntosh, andM.R. Leeder. 1998. Reversal magnetostratigra-phy and radioisotopic geochronology of thePlio-Pleistocene Camp Rice and Palomas For-mations, southern Rio Grande rift. New MexicoGeological Society Guidebook 49: 229–236.

Madden, C.T. 1980. Earliest isotopically datedMammuthus from North America. QuaternaryResearch 13: 147–150.

Madden, C.T. 1983. More earliest isotopically dat-


ed Mammuthus from North America. Quater-nary Research 19: 275–277.

Madden, C.T. 1995. Even more earliest isotopi-cally dated Mammuthus from North America.Quaternary Research 43: 265–267.

Maldonado, F., and A. Atencio. 1998. Preliminarygeologic map of the Dalies NW quadrangle,Bernalillo County, New Mexico. U.S. Geolog-ical Survey Open File Report 97–741, scale 1:24,000.

Maldonado, F., S.D. Connell, D.W. Love, V.J.S.Grauch, J.L. Slate, W.C. McIntosh, P.B. Jack-son, and F.M. Byers, Jr. 1999. Neogene geologyof the Isleta Reservation and vicinity, Albu-querque basin, central New Mexico. New Mex-ico Geological Society Guidebook 50: 175–188.

Martin, L.D., and C.B. Schultz. 1985. Small mam-mals of the Seneca and Sappa local faunas (postOgallala of Nebraska). Institute for Tertiary-Quaternary Studies, TER-QUA Symposium Se-ries 1: 163–179.

Martin, R.A. 1979. Fossil history of the rodentgenus Sigmodon. Evolutionary Monographs 2:1–36.

May, S.R. 1981. Repomys (Mammalia: Rodentiagen. nov.) from the late Neogene of Californiaand Nevada. Journal of Vertebrate Paleontology1: 219–230.

Miller, W.E., and O. Carranza-Castaneda. 2001.Late Cenozoic mammals from the basins ofcentral Mexico. Bollettino della Societa Paleon-tologica Italiana 40(2): 235–242.

Miller, W.E., and O. Carranza-Castaneda. 2002.Importance of Mexico’s late Tertiary mamma-lian faunas. In M. Montellano Ballesteros andJ. Arroyo Cabrales (editors), Avances en los es-tudios paleomastozoologicos en Mexico: 83–102. Serie Arqueologıa, Instituto Nacional deAntropologıa e Historia.

Morgan, G.S., and R.C. Hulbert, Jr. 1995. Over-view of the geology and vertebrate paleontol-ogy of the Leisey Shell Pit Local Fauna, Hills-borough County, Florida. In R.C. Hulbert, Jr.,G.S. Morgan, and S.D. Webb (editors), Pale-ontology and geology of the Leisey Shell Pits,early Pleistocene of Florida. Bulletin of theFlorida Museum of Natural History 37, Pt. II:1–92.

Morgan, G.S., and S.G. Lucas. 1999. Pliocene(Blancan) vertebrates from the Albuquerquebasin, north-central new Mexico. New MexicoGeological Society Guidebook 50: 363–370.

Morgan, G.S., and S.G. Lucas. 2000a. Plioceneand Pleistocene vertebrate faunas from the Al-buquerque basin, New Mexico. New Mexico’sFossil Record 2. New Mexico Museum of Nat-ural History Science Bulletin 16: 217–240.

Morgan, G.S., and S.G. Lucas. 2000b. Biostrati-graphic significance of late Neogene vertebrate

fossils from the Gila Group, Pearson Mesa,southwestern New Mexico and southeasternArizona. New Mexico Geological SocietyGuidebook 51: 211–220.

Morgan, G.S., S.G. Lucas, and J.W. Estep. 1998.Pliocene (Blancan) vertebrate fossils from theCamp Rice Formation near Tonuco Mountain,Dona Ana County, southern New Mexico. NewMexico Geological Society Guidebook 49:237–249.

Morgan, G.S., S.G. Lucas, P.L. Sealey, S.D. Con-nell, and D.W. Love. 2000. Pliocene (Blancan)vertebrates from the Palomas Formation, Ar-royo de la Parida, Socorro basin, central NewMexico. New Mexico Geology 22: 47.

Morgan, G.S., and R.B. Ridgway. 1987. Late Pli-ocene (late Blancan) vertebrates from the St.Petersburg Times Site, Pinellas County, Flori-da, with a brief review of Florida Blancan fau-nas. Papers on Florida Paleontology 1: 1–22.

Morgan, G.S., P.L. Sealey, S.G. Lucas, and A.B.Heckert. 1997. Pliocene (latest Hemphillian andBlancan) vertebrate fossils from the Mangasbasin, southwestern New Mexico. New Mexi-co’s Fossil Record 1. New Mexico Museum ofNatural History Science Bulletin 11: 97–128.

Mou, Y. 1997. A new arvicoline species (Roden-tia: Cricetidae) from the Pliocene Panaca For-mation, southeast Nevada. Journal of VertebratePaleontology 17: 376–383.

Mou, Y. 1999. Biochronology and magnetostratig-raphy of the Pliocene Panaca Formation, south-east Nevada. Journal of Vertebrate Paleontolo-gy 19(3, supplement): 65A.

Needham, C.E. 1936. Vertebrate remains fromCenozoic rocks. Science 84: 537.

Oelrich, T.M. 1953. Additional mammals from theRexroad fauna. Journal of Mammalogy 34:373–387.

Opdyke, N.D., E.H. Lindsay, N.M. Johnson, andT. Downs. 1977. The paleomagnetism and pa-leomagnetic polarity stratigraphy of the mam-mal-bearing section of Anza-Borrego StatePark, California. Quaternary Research 7: 316–329.

Repenning, C.A. 1987. Biochronology of the mi-crotine rodents of the United States. In M.O.Woodburne (editor), Cenozoic mammals ofNorth America: geochronology and biostratig-raphy: 236–268.Berkeley: University of Cali-fornia Press.

Repenning, C.A. 1992. Allophaiomys and the ageof the Olyor Suite, Krestovka Sections, Yaku-tia. U.S. Geological Survey Bulletin 2037: 1–98.

Repenning, C.A., and S.R. May. 1986. New evi-dence for the age of lower part of the PalomasFormation, Truth or Consequences, New Mex-ico. New Mexico Geological Society Guide-book 37: 257–260.


Robertson, J.S. 1976. Latest Pliocene mammalsfrom Haile XV A, Alachua County, Florida.Bulletin of the Florida State Museum, Biolog-ical Sciences 20(3): 111–186.

Rogers, K.L., E.E. Larson, G. Smith, D. Katzman,G.R. Smith, T. Cerling, Y. Wang, R.G. Baker,K.C. Lohmann, C.A. Repenning, P. Patterson,and G. Mackie. 1992. Pliocene and Pleistocenegeologic and climatic evolution in the San LuisValley of south-central Colorado. Palaeogeog-raphy, Palaeoclimatology, and Palaeoecology94: 55–86.

Rogers, K.L., C.A. Repenning, F.G. Luiszer, andR.D. Benson. 2000. Geologic history, stratig-raphy, and paleontology of SAM Cave, north-central New Mexico. New Mexico Geology22(4): 89–100, 113–117.

Ruhe, R.V. 1962. Age of the Rio Grande Valleyin southern New Mexico. Journal of Geology70: 151–167.

Schultz, C.B., L.D. Martin, L.G. Tanner, and R.G.Corner. 1978. Provincial land mammal ages forthe North American Quaternary. Transactionsof the Nebraska Academy of Science 5: 59–64.

Seager, W.R., M. Shafiquillah, J.W. Hawley, andR.F. Marvin. 1984. New K-Ar dates from ba-salts and the evolution of the southern RioGrande rift. Geological Society of AmericaBulletin 95: 87–99.

Smith, G.A., and A.J. Kuhle. 1998. Geologic mapof the Santo Domingo Pueblo quadrangle, San-doval County, New Mexico. New Mexico Bu-reau of Mines and Mineral Resources, Open-file Digital Map 26, scale 1:24,000.

Strain, W.S. 1966. Blancan mammalian fauna andPleistocene formations, Hudspeth County, Tex-as. Bulletin of the Texas Memorial Museum 10:1–55.

Tedford, R.H. 1981. Mammalian biochronologyof the late Cenozoic basins of New Mexico.Geological Society of America Bulletin 92(pt.I): 1008–1022.

Tedford, R.H., T. Galusha, M.F. Skinner, B.E. Tay-lor, R.W. Fields, J.R. Macdonald, J.M. Rens-berger, S.D. Webb, and D.P. Whistler. 1987.Faunal succession and biochronology of theArikareean through Hemphillian interval (lateOligocene through earliest Pliocene epochs) inNorth America. In M.O. Woodburne (editor),Cenozoic mammals of North America: geo-chronology and biostratigraphy: 153–210.Berkeley: University of California Press.

Tomida, Y. 1987. Small mammal fossils and cor-relation of continental deposits, Safford and

Duncan basins, Arizona, USA. National Sci-ence Museum, Tokyo, Monograph 8: 1–141.

Vanderhill, J.B. 1986. Lithostratigraphy, verte-brate paleontology, and magnetostratigraphy ofPlio-Pleistocene sediments in the Mesilla Ba-sin, New Mexico. Unpublished PhD thesis,University of Texas, Austin.

Wang, X., R.H. Tedford, and B.E. Taylor. 1999.Phylogenetic systematics of the Borophaginae(Carnivora: Canidae). Bulletin of the AmericanMuseum of Natural History 243: 1–391.

Webb, S.D., and J.P. Dudley. 1995. Proboscideafrom the Leisey Shell Pits, Hillsborough Coun-ty, Florida. In R.C. Hulbert, Jr., G.S. Morgan,and S.D. Webb (editors), Paleontology and ge-ology of the Leisey Shell Pits, early Pleistoceneof Florida. Bulletin of the Florida Museum ofNatural History 37, Pt. II: 645–660.

White, J.A. 1987. The Archaeolaginae (Mamma-lia, Lagomorpha) of North America, excludingArchaeolagus and Panolax. Journal of Verte-brate Paleontology 7: 425–450.

Wilson, R.W. 1949. Rodents of the Rincon fauna,western Chihuahua, Mexico. Carnegie Instituteof Washington Contributions to Paleontology,Publication 584: 165–176.

Woodburne, M.O. 1987. Definitions. In M.O.Woodburne (editor), Cenozoic mammals ofNorth America: Geochronology and biostratig-raphy: xiii–xv.Berkeley: University of Califor-nia Press.

Woodburne, M.O. 1996. Precision and resolutionin mammalian chronostratigraphy: principles,practices, examples. Journal of Vertebrate Pa-leontology 16: 531–555.

Woodburne, M.O., and C.C. Swisher, III. 1995.Land mammal high-resolution geochronology,intercontinental overland dispersals, sea level,climate, and vicariance. In W.A. Berggren, D.V.Kent, M.-P. Aubry, and J. Hardenbol (editors),Geochronology, time scales, and global strati-graphic correlation. Society for Economic Pa-leontology and Mineralogy, Special Publication54: 335–364.

Zakrzewski, R.J. 1967. The primitive vole Og-modontomys from the Late Cenozoic of Kansasand Nebraska. Papers of the Michigan Acade-my of Science, Arts, Letters 52: 133–150.

Zakrzewski, R.J. 1998. Additional records of thegiant marmot Paenemarmota from Idaho. InW.A. Akersten, H.G. McDonald, D.J. Meldrum,and M.E.T. Flints (editors), And whereas . . .Papers on the vertebrate paleontology of Idahohonoring John A. White, Vol. 1, Idaho Museumof Natural History, Occasional Paper 36: 50–55.

chapter 12 mammalian biochronology of blancan and irvingtonian

Documents