Bollenino delh Societh Paleontologica ltaliana 43 (3),2004 rssN 0375-763336r-382 2 pls. Modena, Dicembre 2004

Eoderoceratidae (Mollusca, Ammonoidea) from tht

Central Apennines, related to the Sinemurian-Plierthe Mediterranean area

Federico VExruRI Carlo NnNNARoNE Massimiliano BIlor

Dipartimento di Scien ze dellaTerraUniversitl di Perugia

KEY IVO RD S - Mo llus cA, Ammono idea, Eodero ceratidae, S in emurian - P liens b ac h ian boui

ABSTMCT - The Jurassic calcareous successions of the "Corniola" unit in the lJmbria-known beds referable to ti, lower Pliensbachian of the eitire Meditercanean Tbthys. These bedsin this aret ofrht global faunal renewal arsociated"*;ttt the Sinemtrian-Pliensbatbia, transition.afrer the disippeirarcebf fch;oceratidae (as Paltechioceras/, and, in the Apennines, it consists o.(mall, t*ooltl, Polymorihitidae, lacking a keel), Catriceras (primitiae anl morphologically qui,ukn keeled and ti;rttttl, Galaticeras (*att-otturrence), Radstockiceras . This bioeu/nt is-afconi.t. b the more o, less clo,mplete loss of the ornumentation, u,ith the transition.fom b;spiyqyg ,1Dresent DaDer deak taith the Eoderoceiatidae found in the rich fossiliferous bed-"Wnturi'78" (('Quorry'

(i4ount Acuto), uthich represents a iubstantial ,rrt*iftoipared to undoubtedly Sinezio"ti Oe considered the frst afiei-Sinemurian record (beginni"s ofrhe 'Teffaspidoce-rai quadr

All the taxa reDresented in our collection (67 speii*"rrr, lnThidlns some forms lefr wiihoutious morphological'and stuctural (namely sutural)'features, and tbeffire wi think ihat they m,su bfam ily, th it we ca lled Param i ro dero cerati n ae.'

Foi our specimens we recognizedfour species, onb one of u,hich.(Paramicroderoceras tf \itfThe remainiiq three s\ecies arl ;nclidcd in two new, here

-proposed {enera: Omode roceris (wh

well as O. cfTarinodosum, which is aform comparable ilth'a ta*in preuiously assigned toEpinew species P. picenum/.

Tht orrttntt of an inner monos\inate Dhase ofdeueloDment in the netil {enus Omoderocerathe sooliation of thi Eodzroceratoidia was i ,omn[ex panirn, includins a paidomorphic transitioonri (this mon'ospinate character is well establiihed in Caleites, Milt"oc.r"r and to*t yet unde:lnte Sinemurian', this uariation was mainly a peramorphosis, simply occurring with thi change 1smooth outer whorls (this is, for example, iht tatt ofBpiderocetis).

The GSSP of the Sinemurian-Pliensbachian boundary proposed for the Wine Hauen sectituides a good refeience for Boreal and Sub-boreal regions (Nort[-Wesi Europe), but not for theetc.). Hoere, in"fact, thi stardard biosnatigraphic citeria that characterize ihe beginnini of tbe red'in the staioty7e with Bifericeras don?vini, and/or presence ofTevaspidoceias qu-adtat-"the Sinemurianl?liensbachian boundary cannot be ideittified wiih precision and, in- the best casections for the early Pliensbachian lacki reliabilitv and resolution beyond the Subzone scale. Sincu.,ith aiceotabte cohfrdence the exDected correkti'o, potrrtial outsirt the Boreal domain, d st/d.t,am basel on the tintrt knowledse, misht haue a ialaeogeographic ualue limited merely to that

{rttorytt. ,As a .matte, tft* 1 Tatifcition of thi aboui-*"triioned GSSP might fornially notPliensbachian in the entire Tbthys.

The difficulties in establishinq careful correktions between Boreal and MeditennneAn Zoneby a numb"i of pakeobiogeograpE;t oid/or pakeoecologic factors. T'his must induce the researcsiudies, apeciilfy in the frthyai domain, wltere, exceptln-the Apenninel the record for the firsr

RIASSUNTO - [Gli Eoderoceratidae (Mollusca, Ammonoidea) nella "Corniola" dell'A

Pliensbachiano in area mediterranea] - L,e successioni calcaree giurassiche aPPartenenti alkcontenaono dei liuelli riferibiti at Plieisbachiano inferiore che tori probabilmiite i piil antichi,o datT importanti per?elineare in quest'areA il rinnouamentofaunistico globnle assiciato al palad ammoiit; qutti cambiamento iuuiene dopo k scompArsA.ZrSlj Echif,ceratidae (come Paftecme di ,o*pirrc concomitanti: Furlites (piccoli Polymorphiti"dae lisci e senzt care.nA, che(Tropidoceitinae primitiui, morfologicamente assai airiabil;, ry(.pilt o meno euoluti, lenticolatsa ii massa), Raditockiceras. ntt b"ioeuento b accompagnato dalli spoliazione degli Eoderoceradell'ornamentazione, con passagio da forme bispinate Z *onrspinite o spoliate.

"ll presente lau,

uati nel ricco liuello fossilifero 'Vnturi'78" (bioeuento a CatriCeras catriense) della Cat,a del ['

nouamento sostanziile riipetto a faune indubitabilmente sinemuriane, ed anche Per questo dot'post-Sinemuriana (inizio'della Zoro o 'Tetraspidoceras quadrarmatum

") dell'Appeinino.'

Tutti itaxa rappresentati nel nosto mateiiok (67 esinplari. cotnprese alc,tii lbrme ilon r't':#",::,::;::::,:*:i'*;n'f';:;*::##'x!;,':t';i"l:;":;:;;:,'::,;:"i,:,:::,ii,,tti;i,'iti"l:,,ii),

362 F. VENTUN, C. NANNARONE, M. BILOTT,

Per i nosni esempkri abbiamo riconosciuto quatto specie, di cui solo una (Paramicroderaenere sih noto. Le ristanti ne sDecie sono state iicluse in'due generi nuoai, di cui uiene aui p'prrnd"'k

nuoaa specie O. canti"n.rrr. ed anche O. cf larinoJot.t-, cioi una forma confroitEpideroceras) e Paraderoceras (istituito per k nuoat specie P. picenum/.'

LA presenz,a di uno stadio interno monospinato nel nuouo'gene.re Omoderoceras testimontore, k sioliazione degli Eoderoceratoidea i auuenuta con un passagto pedomorfico da giri internsi ? ooi'affermato ine"leiter, Miltoceras ed alcuni taxa mediterdnei- ancorA ineditil.-Nel Siner,di iioo iira*orfico, com\ortundo sokmente un transizione da giri interni e medi bispinati a lisc'

If GSSP let limite'Sinemuriano-Pliensbachiano Droposto"per k sezione di Vine Hauen (kun buon riferimento per le regioni boreali e sub-bortafi Guropi Nord-occifuntale), tnd non per qecc.), doui i principi biosnaiigrafici standard che caratterizzano l'inizio del Lias medio (pVagitBifericeras donovani, e/o lreienza di Tetraspidoceras quadrarmatum,) non sono appliuPliensbachiano non pub tttirt indiuidunto con' precision€,

-e, nelk migliore delle ipotesi,' k ,

Pliensbachiano inferiore perdc affi.dabitith e risofuzione oltre il liuello di"Sonozona. PoichC k setaccettabile sicureiza il [ouuto iitenziate di correlazione al di fuori del dominio boreale, uno strbasato sulle conuscenze attualt potrebbe auere un ualore paleogeografico esclusiaamente limitatoco troppo ristetto. Di fono, s;e'si ratificasse it GSSP in' quesTioir,"si potebbe impedire forma,Ptieni hachiano nell' iniera Tbtifu

Le difficohh incontrate nel correkre AccurAtamente le Zone boreali e mediterranee per il Pliead un inslbme di fanori paleobiogeografici e/o paleoecologici: questo deue spingere lz ricerche a nmente nel dominio teti/eo, doue,Z foit l'Apfennino, li docimentaz;oni delk prima Zona del

FORE\TORD

The. present work fits into the researches onammonite biostratigraphy that oyr ?gp?ttment car-ries out since many years in the Umbria-MarcheApennines. Here , the calcareous-m arly successionibeloneine to the lithostratisraphic units of Corniola,MarnE aJt Vt. Serrone and"Rosso Ammonitico yield-ed an impressive documentation for the Lias, startingfrom th; early Sinemurian (Guide GeologichERegionali no 7, 1994) as far as the entire Toarcian(Venturi, 1999). Nevertheless, there are many issuesleft to investigate, both for the biostratigraphy andfor the underitanding of the evolutive relationshipsbetween the main s/stematic groups (superfamili-esand families), also in relation to-the vicissitudes of thepalaeogeoqr.aphigdomains. r, .

From this point of view, one of the most interest-i.g bioevents

-is represented by the fossiliferous bed

"%ntu ri'78" from the the Paliareto Qu arry (Mount

Acuto, Umbria-Marche Apennines; Text-fig. l), char-acterised by a very rich faunal content (Venturi,1978; Venturi & Bilotta, 2001). Its chronostrati-graphic position h."r. been the object of contrastinglnterpretauons: ongrnally, this b6d, also known asCatriceras catrieme

-bioevent (Faraoni et dl., 1996;

Dommergues et Al., 1997a), was attributed to the lateLotharinfian -early Carixian (Venturi, 1978), butsubsequ.it Authors erroneously placed it in the mid-dle Pliensbachian (Ibex Zonel Valdani Subzone:Dommergues et dl., 1984; Dommergues et dl.,1997a). It has been proved (Venturi & Bilotta, 2001)that this bioevent precedes the Miltoceras sellae beds,and therefore thaf it cannot pertain to the middlePliensbachian, but the issue of its precise dating was,by now, never completely resolved. According to theresults of recent studies (Faraoni et Al., 1996; Venturi& Bilotta, 2001) and current researches (includitgthe present work), the bed

"Venturi '78" contains a

Text-fig. I - Geographic location of the Pallareto, Bosso andFurlo sections.

Mount Pietralata o

BOSSO

Mount Acuto

A

LUSSrc EODEROCERATIDAE AMMONITES FROM THE APENNINES 363

fauna characterized by numerous Galaticeras Spathand many til(a referable to the Eoderoceratoidea,includitg the first Thopidoceratinae (CatricerAsVenturi)

- and smooth Polymorphitidae (Furlites

Venturi & Ferri). This represents a substantial renew-al compared to the

- undoubtedly Sinemurian

Echioceratidae assemblages. Since, historically, theSinemurian-Pliensbachiat bound ary corresponds forthe ammonites to a qlobal-scale faunal renewal,marked by the Echioceritidae disappearance _and bythe subsequent Eoderoceratoidea diversification(Dommergues & Meister, 1992; Dommergues et Al.,1996; Merister & Stampfli, 2000; Meister et dl.,2003), we assume that the bed "Venturi'78" shouldbe considered the first after-Sinemurian fossil recordin the Apennines.

Amohg the many forms pointing out the essentialnovelry of,the bed "'Venturit78", thire are the spinedammonites which we believe to constitute a new sub-family of Eoderoceratidae, endemic to Tethys. Theseforms can be ascribed to the genus ParamicroderocernsDommergues, Ferretti 6{ Meister and to rwo newgenera, here created.

According. to some palaeog,elsraphic :econstruc-tions concerning a time interval from the Sinemurlan(Dommergues, 2002), to the Sinemurian-Pliensbachian (Meister 6( Stampfli, 2000), to themiddle Toarcian (Dercourt ei dl., 1993), theApennine region was placed in the eastern part of the*trt.rn Teth"ys. Basing on the areal distribution datafor early Pfi6nsbachiin ammonites, we hypothesizethat, in this area, a sector comprising the Apenninesand at least also middle-eaitern

-Prealps, Sicily, /

Albania, Ionian Greece and Tunisia can be identified.'We believe that this region was separated, from a

palaeobiogeographic poittt of view, itt regard to theheighbouiing ones. At the moment, in fact, the mainril€ present-in the bed "Venturi '78" seem to repre-sent a provincial fauna, endemic to the Sub-domaincalled

- by Meister 6( Stampfli (2000) Alpine

Mediterranean Tethyr.

CHRONO- AND BIOSTRATIGRAPHIC FRAME\TORK

ConnpLATroNS \rITH THE STANDARD ZoNr,s

Basine on ammonite associations, the biostratigra-phv of thi European Pliensbachian refers to a detailedscheme of Zonis, Subzones and horizons defined asstandard (Dean et dl., 196l; Dommergues et dl.,1997a; Hesselbo et al., 2000; Meister et Al., 2003).The first layer of the early Pliensbachian is tradition-"lly determined by the beginnitg of the JamesoniZone (base of the Thylori Subzone). Originallydesigned by the association of Apoderoceras leckenbyiNfrlght) "itd Phricodoceras taylori (Sowerby) (Spath,1923), this beginnitg is now conventionally recog-nized with the presence of Apoderoceras Buckman lA.nodogigas (Q,t.tstedt) , A. leckenbyi, A. spp.l and/or

Tbtrasp i do c eras q uadrarmatum ( D umo rtier) ( S chlaff er,1977 , 1980; Dommergues 6c Meister, 1992;Dommergues et al., 1994b, 1997 a; Hesselbo et Al.,2000; Meister et aL.,2003). This definition allows toidentify the Thylori Subzone throughout North-'Western

Europe, but in most cases its base can beonly tentaiively determined with someEoderoceratoidea requiritg further studies (Hesselboet al., 2000; Meister et aL.,2003).

The biostradgraphic relations with the Tethyanarea are even -5r.'difficult to precise, because theessenti ally Boreal tilra on which is founded the stan-dard zonation are lacking, or very rare, or do notallow sufficient accuracy. Tb obviat6 this matter, alter-native zonations were elaborated (fot instance Bragaet al., 1984; Faraoni et Al., 1996), but their correla-tions with the North-'Western Europe scheme are sdllconsidered tentative (Dommergues et dl,, 1983;Meister, 1995; Dommergues et /tI., 1997a; Meister etdl., 2003), and sometinies subject to Subzone-scaleuncertainties (Dommergues et al., 1997a).

The zonation proposed for the Umbria-MarcheApennines by Faraoni et al. (1996) is the b5st suitedto assess the biostratigraphic position of the bed"Venturi'78".

Originally, it did not show great corre-lation problems with the standard Zones, because itpartialfy recalled the hypotheses of G€czy (1976),*ho atiribuited a Tenasjidottrat quadrarmatum hori-zon to the lower part of the Jameio ni Zone, thus sub-stantially asreeine to the traditional definition of thebase of iheTliens[achian. It is known, in fact, that Tquadrarmatum (index ta(on for the first Zone ofFaraoni et dl., 1996) can be found together withApoderocerAs nodogigas in some central Europe regiols(Dommergues EeMeister, 1989, p. 467): Burgundyand Jura (France), Causses and South-'Western France(Dommergues 6( Meister, 1992, p. 213-214;Dommergues , 1993), and, apparently, sometimes inGreat Britain too (Dommergues & Meistet 1992, p.216). Elsewhere (French

-and Swiss Prealps) T

quad,rarmatum replace s A. nodogigas (DomTelguet. +Meister, 1992; Dommergues et al., 1997a). For thisreason, one could be indilced to believe that the baseof the Thylori Subzone (Boreal Palaeoprovince) andthat of the T quadrarmAtum Zone (MediterraneanTethys) were coirelatable without too much difficul-ties. However, detailed comparisons are not allowedby the inadequacies (both sidimentary 1nd of fossilcontent) whiih charac terize most part of the succes-sions just at the Sinemurian-Pliensbachian transition.The mafter is further complicated after an accuratestudy of the Apennine Formt unti l now calledTenispidoceras quadrarmAtum, which must be actual-ly asiribed to another genus. In fact, thev do notseem to have spherocone or sub-spherocone innerand middle whorls , e feature that, according toDommersues 6{ Meister ( I 9 99) , character izesTetraspido\eras s.s. (i.e. T gr. quadrarmatum\. Theabsence for the Apennine spEcimens of an ontogenet-

364 E VENTURI, C. NANNARONE, M, BILOTTA

ic development diagnostic for TbnasyidocerAs, andthus the need to inc-lude them in a different tanon,have already been noted by Dommergues et Al.(2000). These Authors ProPosed an attribution toParamicroderoceras, as the presence of intercalated lat-eral second ary ribs gives evidence in favour of thisdesignation, b.tt *e f,elieve that this character is notsuffi"cient. In fact, the inner whorls of our

" T

quadrarmatum" , are poorly known, but ,!t.y seemfikelv to correspond to some small unclassified speci--.trt from th6 unpublished Ful lumachella oF theFurlo Pass (Pl. 2, figs. 5,9a-b, 12) and to two imma-ture individuds from the Pallareto Quarry (Text-fig.

7b; Pl. l, fig. 4). All of them are cadicone, involuteand broad, i"ith a depressed sub-trapezoidal whorlsection and a monospinate inner stage, _in contrastwith true Paramicroderocerus at the sarie diameter. Inour opinion, considering these forms as a new genusis to be preferred, because their inclusion inParamicrodirocerAswould render the til(on nearly use-less, expanditg to9 much its already wide morplrg-loeic rinse, and further muddling its stratigraphicdiitributiSn (which does not seettt-to be sufficiendyknown, according to Blau, 1998; Dommergues et dl.,2000;

'S7'ilmsen it al., 2002). Among the specimens

attributed in the literature to T quadiarmatum, those

found by Dommergues & Meister (l99lt Pl. l, figt.5-6, p|.2, fig. 3, p|.4, Ftg. la-b) in the Meillerie sec-tion lnorthe-rn Chablais, Sub-briangonnais domain)are the only ones that can be considered similar to ourforms, resembling indeed a medium-sized individualfronr the Ful luriachella of the Furlo Pass. Actually,for their morphology with sub-platicone coiling,rounded section and large spines, none of theseammonites can be striltly compared with theTbtras p i do ceras genero Wpe, *hi.h hai s ub-spheroconeinner'and midtrle whorls, high sub-traperoidal outerwhorl section, and small spin-es (at least, judgitg fromthe figure in fukell et dl., 1957).

In conclusion, although we can confirm theabsence of the rypical forir of T quadrarmAtum inthe Apennines, thf same is not tttt. for Apofurocerus,becauie in the Ful lumachella, a fragment refereableto this genus was recendy found (whereas in bed"Venturi'78" this tu(on I missing). This specimenwill be figured and widely described in a forthcomingDaDer foiusins on the spathic lumachellas Ful , Fu2^""i

Fu3 of thJ Furlo Pasi: for the moment we can saythat its ornamentation and whorl section are verysimilar to those of the A. subtriangukre (toung 6(Bird) presented by Howarth (2002, pl. 6,. figl , !-5).This d"t.t-, however, does not eliminate the-difficul-

\]Palaeoprovinces\

Stages \

BOREAL(Meister et al., 2003)

MEDITERRANEAN TETHYS(This paper)

EARLYPLIENSBACHIAN

Zones Subzones Horizons Bioevents Zones

Uptoniajamesoni

Jamesoni U. bronniTropidoceras

flandrini

Miltoceras

sellae

"Polymorphites"

appenninicusBrevispina

Pl. submuticum I

Pl. tenuilobusPl. brevispina I

Pl. brevispinoides

Farinaccites

clavatus

Polymorphus ? P. polymorphus I

E.(C.) biruMiltoceras

---19-Y:-lP-:--

Taylori

Phr. taylori "Tetraspidoceras

quadrarmatum" I

Catriceras cf.

_ _ - _qq!!ry !!!e !!te - - - -

'Tetraspidoceras

quadrarmatum"A. nodogigas I

T. quadrarmatum I

A. aculeatum

B. donovani Catriceras cotriense

LATESINEMURIAN

? ,l ,l ,l

,lEchioceras

raricostatumAplanatum

Pal. tardecrescens I

Pal. romanicumPaltechioceras

romanicum

Text-fig . 2 - Correlation hypothesis among th9 _late. Sinemurian-early Pliensbachian biostrzons/bio.n.ttir) for rhe BoreJand Mediterranean Palaeoprovinces. Note that, by now, the Cnot be safelv correlated to rhe Bifericeras donouani horizon. This fact has impoitant implic:rion of the Sitt.-,trian-Pliensbaihian boundary and for its actual applicabilt.'' at a global s

LASvC EODEROCEMTIDAE AMMONITES FROM THE APENNINES 365

ties in establishing accurate correlations between theApennine zonation and the standard one, and as toth^is subject, we can only present hypothetical rela-tionships (Te xt-frg. 2).

THE C,arucrn qs IATRIENSE BIoEVENT

The use of zonal schemes based upon differenttal€ implies many correlation problems even if werestrict

^tn. study'to the Mediterranean Tethys and

neighbouring areas: an example is given by the casesof Flungary (Geczy, 1976; Do*ti.rgues'& G€czy,1989) ind Turkey (Otkun, 1942; Bremer, 1965;Alkaya 6( Meister, 1995), where the successions areoften incomplete, and the ammonites adopted in theApennines "i ,otal markers are seemingly-lacking.-

Local-scale correlations are far more accurate,therefore we will limit iust to the Apennine area. If wewant detailed indications on the position of the faunastudied in the present paper, it is necessary to analYzethe relationships ben"e6n the rype s..iion of ihe"

Tbtraspidoceras quad.rarmntum" Z6ne (Bosso section)and tlie Pallareto Quarry section, xs they show non-neelieible differet.it, both in thickness'and in fossil.oiltJttt (quantitative and qualitative). In thePallareto seltion in fact, where the succession is anintermediate between a basin and a structural highone, the fossil record is abundant only in bed"Venturi'78" (Venturi & Bilotta,200l), while in theBosso section it is scarce, but distributed over morelayers, and it represents a definitely thicker basin suc-cession. Furthe-rmore, in the Bosso section, the

" T

quadrarmatum" Zone lower boundary was located byin assemblage with merely GalaticerAs sp. andRadstockicerai gemmellaroi (Pirmpeckj) (bed 59), .tb.index species bccurring iust abbve

'(from bed 46),

after the fauna of Hd' 45, which also containsCatricerns. On the other hand, in the Pallareto sec-tion,

" T quadrarmntum" is nearly absent (beitg reP-

resented tiy only two nuclei), bur there are numerousspecimens of

'GakticerAs, various Eoderoceratidae

(inainly bispinate, but also mongspinate) - ?n4Polymorphitid". either smooth (Furlitis)_ or ribbed(Caniceias). It was therefore suggested (Venturi &Bilotta, 2001) that the fossiliIerous bed of thePallareto misht have an age either comparable to thatof the base o"f th.

" T qu.o7.rar*Atum" Zon defined at

the Bosso section (beil 39) or earlier.These considerations are supported by recent dis-

coveries made at the Furlo Pass (Grilli Q,t"try), in asuccession of structurd high, formed by many spath-ic lumachella beds. The fa.-una of the stiatigr"phic"llylowest bed ever recognized (the already-mentionedFul, matter of a forthcoming publication) aPPears tobe chronologically close to the Pallareto assemblaggfor the contemporaneous presence ofEoderoceratidae, CatricerAs and Galaticerts.Nevertheless, it contains also til€ absent in bed"Venturi '78",

including the above-mentioned frag-

ment ascribed to Apod.erocerAs, xs well as smoothammonites that

"ahticipate" some characters of

Gemmellaroceras Hyatt (Furlites and other formsbelongitg to an unpublished microconch gengs). Allthese El.ir.nts seem to show that the age 6f the Fullumachella is closer to that of the bedsZ 5-46 of theBosso section (tentatively correlated to theApoderoceras nodogigas horizon of the standa rd zona-tion), and there6ft that it may be later than thePallareto fossiliferous bed (Text-fig. 3).

For all these reasons, we curre-ntly think that theage of the Catriceras catriense bioevent can be com-p"ared to that of the bed 39 of the Bosso section, thuswe can confirm the biostratieraphic attribution for-merly prgqosed UyY.^"r.,rti (li7d). U1Qrtunately, weare not able to specifr its precise position comParedto the Bifericeras doiot ani horizon (the first of theThylori Subzone), so we do not know if it actuallydocuments the base of the Pliensbachian in theApennines. In our area (but it seems to be a nearlywbrldwide condition) it is sdll lacking a truly com-plete and continuous succession, that-would permit^to

verifr the presence or the absence of -earlier

Pliensbachian bioevents. This fact is clearly exempli-fied by the two Bosso river valley sections (Stirpetoand Bbsso), where, between the list Sinemurian^fos-siliferous beds and the first Pliensbachian ones thereis a barren interval of more than 5 metres, to which isadded a hiarus due to a fault (with a probable slip of6 metres), that implies the,lack of at least 20-40 beds.

THE EODEROCERATID'AE OF THE PALI.ARETO

MnrH oDoloc ICAL oBSERVATIoNS

For the systematic study of the Eoderoceratidaesubject of the present work, we based on a quite"reitrictive"

approach. For practi.."l purposes we pre-fer, in fact, (eicept in very well-documented cases,that is with abundant material and precise strati-graphic references) to keep not excessive ranges ofvariabiliry especially for tilra whose assigned rank is

senus and/of speciis. 'With

this method the differ-E r..r (in -orphology and in geographic and strati-graphic distribution) are markidli uhderlined, thusharring a precise characterization for the formallynamed groups. In our experience, the long time inter-val rep6r.tt.d even by " single ammonitJ Zone (last-itg some 500.000-1.000.000 years) is generally regis-ter d in rock bodies where the sedimentation and fos-sil record are often disturbed, episodic or very dis-continuous (sometimes despite their aPParent phvsi-cal continuiry). This generates so much uncertaintiesthat we believe far more useful for the biostratigraph-ic resolution only the taxa with clearlv restricted mor-pholory and stratigraphic-geographic distribution.Such fioups are easifv recognizable, independentlv oitheir possible biological value.

To obtain greater completeness in the svstematic

366 F. WNTURI, C. NANNARONE, M. BILOTA

@-l,@f-J,@4 l

39

37

46

45

Fu3e

t " ,O@

H'*Grilli Quarry(Furlo Pass)

Pallareto Quarry(Mount Acuto)

LEGEND

rT.ll=Fl

E Ornfrm

l 9

l6t 5 l9lsl

calcnroous bed

bed with chert

bed with cnsinitic layer

bGd with stylolite

slump ; [ ' -

biocvent of thcEchiocerus raricostatum Zcl.nre(Late Sincmurian)

biocvent of the' T e traspi doc e tra.s quadrarmalum "

Znne (Early Pliensbach ian)

biocvent ol theMiltoceras selloc7rrlrc (Early Pliensbach ian)I

I

€ncrinitic bcd I

- Bd Vernri ?t

PROBLELTANC INTERVAL

(sINEIWrt NAN-PLIENS BAC HIAN Tn/'NS Ino t9

LEGEND

Kil

@

ABosso River section

(situation at APril 3, 1999)

Text-fig.3 - Short-distance biocorrelation.among three lower Pliensbachian sections of the;il;"; Tri.z.The Bosso River seltion-(in the middle) is the most extended one, and it

;;;il; ff;;.rriot s thir it rhe only ol the thre. pr.i.ttted sections that contains late Ipri;;i;;t;;tbeJ 16: vici"iA;ir^"tia Pbsechiotrr^\. The Pallareto Quarry section (on theriiio"J'; t.rrn berween .o*pl.re successions and incomplete ones, and contains three encrition (on the right) is an incbmplete and reduced succession of sffuctural high. .The bed

"Ve"-il;f if"-;f;hei5rti"t.ro qtt,"rry (Catriceras catiensebioevgni) should€orres

Bosso section, *ttit. itt.-p"f bioi"."t frJrr tht Furlo Pass is supposed to be more or less ccThe Fu3 bed'(tut;[toitr^"o". qp. ""d

"Polymoryhltes" nov. rp. b^ib.vgnt), probably represen'lne Zoie, and ih.t.fore it is inferred to pt'eced6 the bioevettt lo.ated on the top of the bed

distinctions we iointly examined all the available ele-ments: morphofogy (toiling, shell shape, ornamenta-tion), ,tructure fConformation of the suture line),stratigraphic and geographic localization.

Sysrnv,arlc DESCRIPTIoNS

In the fossiliferous bed "Venturi '78" of thePallareto Quarry that, as already stated, is placeablear the base of the " T quadrarlmatum" Zone (earlyPliensbachian), 67 Eodeioceratidae specimens repre-sented by silicified internal moulds were found.Gener"lly, they show most part of tlle phragmoconeand at least the beginni.g oT the body ihamber. Thedescription of the identifi"'ed forms is presented below,with di"gttot.t that partially retain some ideas ofVenturi 5. Ferri (2001). T6e terminology used indescribi"s the general shape of the shell and its orna-mentation is tliat of Ark efi et al. (1957), also Presentin Venturi (1985), Venturi 6( Ferri (2001). For thesuture line we adopted the same complete nomencla-ture (both for lobes and saddles) ofVenturi (1978,1985, 1997), that can be found also in Viedmann 6cKullmann (1981).

For each species the followitg biometric Parame-ters are eiven, stated in millimeires (fot linear mea-suremenis) or as adimensional numbers (fot ratios):diameter (d), umbilicd diameter (u), whorl height(h), whorl width (*), umbilical ratio or involutionindex (u/d), whorl shape or flattenittg index (w/h),height ratio (h/4), widih ratio. (w/d). Esdmated val-ues are preceded by the symbol -.'We

would finally trot. that, accordi.g to theICZN (1985) recomendations, the desinence adopt-ed in the present paper to designate superfamilies is -

oidea (rather than th. sdll witrespt.td, but formallyless correct, -aceae).

Superfamily EooEnocEMToIDEA Spath, 1929^Family iiooERocEMTIDAE Spath, 1929

Subfamily PnnnvICRo DERocERATINAE nov. s ubfam.

Typt genas Paramicroderocerns Dommergues,Ferre[ti & Meister, 1994.

Pioy"osis - Evolute to involute shell, with whorl

secdon variable in shape (sub-rectangular, sub-trape-zoidal, sub-quadrate) .

The ornimentation is rypical of the superfamily,with primary ribs normallv ioining rwo rows of spines(tubeicles on internal -o,t[d) and thinner and ilosetsecond ary ribs, which pasg th9 ventral area withoutinterruption; small intercalated lateral ribs (or striae)are otten present too.

Discriminant for this subfamily is the suture,indented and with arborescent lobes: E as a rule quitenarrow as long as L or shorter (but never longer),with deep -.di"n saddle and sub-parallel or slightlydivergi"s main branches; L with a narrow more or

367

less long trunk, possessing bifid aspect or, as a formderived?om thii, trifid, .iith e*terhal branch havitgthe more or less accentuated tendence to invade theventral area; inclined umbilical lobes, sometimes withU3 nearly perpendicular to L; broad ES and LS 1 sad-dles, with ES bUlique toward the external side.

All the til€ of this sroup are exclusively known inthe late Sinemurian- ea"rly Pliensbachian of the Tethys.

Genus9t"toDERocERAS nov. gen.

TtPt species - Omoderoceras cantianense nov. sP.

Name d.eriaation - From the Greek omds (= simi-lar) and DerocerAs, origin ary denomination ofEo'deroceruts (again from t[e Greek: diros = sheath,shell, test; kirh = horn, due to the resemblance withthe ram horns of the ancient god Zeus Ammon), tra-_ditionally adopted as "termination" in the names ofmany spinous ammonites.

Ttpt locality Mount Catria (Umbria-MarcheApennines).

Tvpic beds - Calcareous-micritic succession of the"Coiiiola", with decimetric calcareous beds and mil-limetric clayey joints; early Pliensbachian.

Material Twenry-eight different-sized - speci-mens, assigned to two tp.ii.t, preserved as silic'ifiedinternal nioulds, without trace of the shell (pro't e-nance: Pallareto Quarry).

Diagnosis Inner whorls moderately involute,with quite broad ribs, almost rectiradiate, ending in asingle- row of spines; middle whorls (sometimesbisiinate) and o,tt.t ones becomine hisher, ellipdc"rd compressed, and tending to lSose"at first thespines, thln to undergo a *ea[ening of the ribs.^

Characteristic is the presence of a ribbed mono-spinate phase, that can be rather short and limitedonly to ihe inner whorls (bemeen the initial smoothstase and the ribbed bispinate middle one), or longer"rJ involvitg outer "td middle whorls (in this casl abispinate ornamentation is never dgvel,op.d). Thetransluon from middle to outer whorls, when itoccurs the spoliation (i.e. the weakening and loss ofthe ornamentation), takes place always quite preco-ciously.

The ventral area, especially in the inner and middlewhorls, is crossed by stcondary ribs; at dmes, on theflank there may be also small intercalated lateral ribs.

The suture'is indented, and possesses the charac-ters of the subfamily: E lobe shorter than L (in smallspecimens this feature is not much evident), withsub-parallel main branches; large and arborescent L,essendally bifid, with outer braich tending to invadethe ,r.ttftd are a; suspensive IJz and

-Ua lobes,

inclined in comparison to L; U2 more or less closed

LUS%C EODEROCEMTIDAE AAIMONITES FROM THE APENNINES

368

on the bottom by U3 ("s a rule more inclined thanU2) and by the dorsal branch of L; ES saddle slight-ly broader than LS l.

Remarks To a quite superficid examination,Omoderoceras may recall some forms assigned in theliterature to Epideroceras Spath, either for its ontoge-netic changes in morphglogy and ornamentation, orfor the general aspect of its sheil. However, the twogenera are well distinguishable, mainly for the fol-lowing characteristics :

- Epiderocerns has a different-shaped whorl section(for ihstance it is higher) compared to that ofOmoderocer*s, xt any stage of development;

- for Epiderocerns an inner monospinate stage wasnever explicitely described {Donovan, 1958, p. 37,fig. 6, do show a drawitg of E. aff. steinmanni (Huflwith inner whorls bearing only one spine, but he doesnot mention this fact in the text], whereas inOmoderoceras this stage is dways present;

- Epiderocerus ofteil mantairis a ribbed stage on thebody ihamber while in OmoderocerAs ribs aie alwayslost in the outer whorls of the phragmocone;

EpiderocerAs looses the ventral second ?ry ribsduringontogenesis, whereas in Omoderoceras this ten-dence"is absent or poorly-developed;

Epiderocerns normally does not seem to havesmall lateral ribs, but in Omoderoceras these are some-times evident;

Epiderocerns has a suture in which the externalbrancli of L lobe does not have the tendence toinvade the ventral area, whereas in Omoderocerns thistendence is clear, and normally is enhanced duringthe growth;

-" Epiderocerus has a suture with a relatively broadE lobe, which possesses divergitg branches, but inOmoderocerAs this lobe is quite

-nairow, with sub-par-

allel main branches;- Epiderocerns has a suture with ES and LS I sad-

dles normally of the same size, whereas inOmoderocerns ES is always a little broader than LS l;

Epiderocerns reaches large size (according - toDonovan, 1958, the diameter for complete individu-als is between2T and 35 cm), but Omoderoceras seemto have only middle size (the estimable maximumdiameter is about 6-7 cm);

- Epiderocerns is safely known almost exclusively inBoreaf or Sub-boreal regions, while Omoderottr^ isby now recorded only in the Tethys;

- Epideroceras is safely known almost exclusively inlate Slnemurian [even if Alkaya 6( Meister, 1995report a species, E nodafissum (Q.t.tstedt), classicilyattributed to the early Pliensbachian], whereasOmoderoceras is by now recorded only in the earlyPliensbachian.

Included species OmoderocerAs cantianense nov.sp. (ryp. species by original designation)

F. VENTURI, C. NANNARONE, M. BILOTTA

Omoderocerns htinodosum (Bremer, 1965)OmoderocerAs cf. htinodosum ?nov. sp

OIvIOOEROCERAS CANTIANENSE nov. sP.Text-fi g. 4a-b; Pl. l, figs l-3

1985 Jamesonites sp. ind. Vrxruru , p. 47 , fig. 48.1996 " EpiderocerAs" ktinodosum Bremer FRRRoNI, MARINI,

Pnt-uNt 6c VrNruRI, pl. 12, fig. 4.2001 " EpiderocerAs" htinodosum Bremer - VnNruru & BtrcTTA,

P.328, : 'ab.2.2001 Epideroceruts sp. ind. VrNruru 6c Fnnnr, p. 127, pl. 11, c.

Name deriuation- From Cantiaro, small town notfar from Mount Catria.

Holotype - Pa78-E19, specimen with the begin-ning of ilie body chamber (Text-fig. 4a;Pl. l, fig.-la-c),

-housed in the Earth Sciences Department,

Universiti degli Studi di Perugia.

ParatyDes - Pa78-E21, specimen with the begin-ning of ihe body chamb.r (Pl. l, fig. 3), and p{Zg-

E24, specimen with only phragmoco-ne (Pl. l, fig.2);both are housed in the Earth Sciences Department,Universitl degli Studi di Perugia.

Typt hcality - As for the genus.

Typit section- Pallareto Quarry bed "Venturi'78"

.

Material - Eleven specimens, includirg the holo-ryPe.

Measurements (in mm) -

N u m b e r d u h w u / d d h h / d d d

Pa78-E18 -52.0Pfl8-EL9 39.7 15.0Pa.78-E20 36.8 r5.2Pa,78-E2l 37.2 l4.lPa,78-E22 28.1 10.0Pa78-E23 28.0 9.90P^78-824 23.2 7.90Pa,78-E25 18.7 6.30Pe78-E26 10.0 3.30Pa78-E27 -9.60 3.70Pa,78-E28 8.80 3.00

1 7 . 5 I 1 . 5r4.0 10.8r2.0 9.00r4.0 9.90l l .5 9.9010.6 8.608.00 6.506.50 5.603.70 4.003.703.20 3.50

0.66 0.34 0.220.38 0.77 0.35 0.270.4r 0.75 0.33 0.240.38 0.7r 0.38 0.270.36 0.86 0.4r 0.350.35 0.81 0.38 0.310.34 0.81 0.34 0.280.34 0.86 0.35 0.300.33 1.08 0.37 0.401.00 0.39 0.390.34 1.09 0.36 0.40

Desription of the holotype - Moderarcly involuteshell, with pooi coil .orr.iitg; inner whori probablyrounded sub-quadrate, tending to rise and bbcomitghieh elliptical."The

ornamentation in the inner and middlewhorls (the embryonal ones are not visible) is repre-sented by ribs with a ventro-lateral row of spines;from the diameter of about 20 mm the ornamenta-tion is completely lost.

LUSSrc EODEROCERATIDAE AAIMONITES FROM THE APENNINES 369

The suture is typical of the genus, with E muchshorter than L (that^invades the ientrd area), and U3nearly perpendicular to them.

Diagnosis - Moderately involute shell, with fmt-growin[ whorl height; rounded sub-qua-dra1e or cadi-Eon. seItion in the-inner whorls, ogival-high ellipticdin the outer ones; rounded umbilical wall.

The ribs, present from the diameter of about 4mm (when th-e smooth embryonal whorls end), arerectiradiate, not much reliefing, enditg with moder-ately long ventro-lateral spines; as far is can be seen,_,r-bili."I spines are never present. At a diameter ofabout 20 millimetres the sliell completely looses theornamentation, or mantains it as iteak, broad anddepressed umbilical bulqes.^

The suture is indenied, possessing the charactersof the subfamily, with the peculi arity that E is about

one half the length of L, and L itself tends to invademarkedly the veitral area, closing E on the boffom.

Remarks and comparisons This species mightremind some forms attributed to Epiderocer*s,because of its loosing of the spines between inner andouter whorls, accompained by e contemporaneousincrease in the whoil heieht' (from rounded sub-quadrate to ogival-ellipticJ), and for its indentedr,rt,tt. line. HJwever, the presence of a single row ofspines is indeed an intereslitg innovation: this char-acter, combined with those" concerning the shellshape and to the details of the suture linl, make O.caitianense substantiallv different from all otherknown forms, and justifies its inclusion in a newgenus and species . -v

Amone the remarkable features, the length differ-ence bewien E and L lobes, os well as the imount ofinvasion of the ventral area by L, are both enhancedduring the ontogenesis.

Stratipraohic distribution Early Pliensbachian(basal p"?t 6f ,h. " T quadrarmntum'( Zone).

OvooERocERAS cf,, uqrlNoDosuM (Bremer, 1965)Text-f ig.7cl-c3; Pl. 1, f igs 5-9,1I

1965 Epiderocerus ktinodosumBxnMER, p. 160, pl. 15, fig.2a-b;tbxt-fig. 3 l.

1985 Hyperfuroceras hungaricum G(uy - VENTURI, p. 46, fig. 47 .1996 " EpiderocerAs" ancyrense Bremer FRnRoNt, MAruNI,

Pnu-lNl & VENIuRI., pl. 12, fig. l.1996 " Epiderocerns" ktinodosum Bremer FRRRoNI, MRruNI,

PnruNI & VrNruRI., pl. 13, figs 1, 5-8.2001 " Epiderocerns" ktinodosum Bremer - VENIUT & BttOTTn,

p. 328, rab.2.200I oEpiderocerAs" sp. ind. VENruru & FERRI, p. 116.2001 " EpidnocerAs" sp. ind. VEvruru & FEnru, p. i 27, pl.l l, i, m.

Materia/ - Seventeen specimens.

Measurements (in mm) -

N u m b e r d u h w u / d d h h / d w / d

Pa78-E0l 52.2Px78-802 47.8Pa78-E03 -51.0Pfl8-804 -4t.5Pa78-E05 4r.0Pe78-806 39.6Pa78-807 32.0Pa78-E08 25.5Pe78-E09 -13.5Pa78-El0 12.6Pa78-El | 12.6P^78-Er2 -12.5Pa78-El3 I 1.5Pa78-Er4 ll.4Pa78-El 5 I 0.5Pa78-El6 - 10.0Pa78-El7 9.40

22.0 18.0r9.2 r5.7

14.0r4.0

16.6 r4.015.8 r2 .9l 1.9 r2.48.50 9.506.00 3.804.r0 4.604.30 4.70

4.303. l0 4 .804.20 4.603. l0 4 .203.00 4.003.00 3.50

13.0 0.4210.5 0.4012.012.3 -0.47rr.4 0.4010.5 0.40I 1.6 0.3710.6 0.334.90 -0.446.10 0 .335.60 0.346.00 -0.355.00 0.274. I 0 0.374. l0 0 .305 .10 -0 .305. l 0 0.32

0.72 0.34 0.250.67 0.33 0.220.86 -0.27 -0.240.88 0.34 0.300.8 r 0.34 0.280.81 0.33 0.270.94 0.39 0.36r . r2 0 .37 0 .42r.26 -0.28 -0.36r .33 0.37 0.48l . l9 0 .37 0 .44t .40 -0.34 -0.48| .04 0.42 0.430.89 0.40 0.360.98 0.40 0.191 .28 -0 .40 -0 . i rt .46 0 .17 0 .54

r s lt-l L

ES

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Lttf-l

tsr-

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EST

Text-fig. 4 - Omofurocents-sutures; a) -O. cantianense holyyPe(Pa78-E19), drawn er e diameter of about 40 mm(magnified abour x 4); b) fragment of the samespecles (Pa78-El8), showing alio the inner part ofthe suture line; drawn at ariesdmated diam-eter of50 mm (magnified abour x 4); c) formdly unclas-sified smdl specimen, belonging to a species ofOrnoderoceras pe rhaps close to O. cantianense;drawn et a diametef of about 13 mm (magnifiedabout * 6) (drawing by F. Venruri).

370 E VENTURI, C. NANNARONE, M. BILOTTA

Remarks and comparisons - For the general shapeof the shell, with biqpinate middle wholls and spine-less sub-rounded section in outer whorls, our speci-mens resemble the species that Bremer ( I 965) calledEpiderocerns latinodostlm. However, in Bremer's(i965, pl. 15, fig.2a-b) holorype, the change of orna-mentation berween middle and outer whorls occursrelatively late, because the bispinate stage is kept untilthe diameter of about 33 millimetres. In our speci-mens the transition between middle and outer whorlstakes place much earliet at around 20 mm (Text-fig.7cl-r3). Furthermore, the inner whorls of the holo-type are considerably more evolute, and it isunknown wether they have a monospinate phase ornot. The evolute stage of our forms is much shorter,and its inner part bEars a single row of spines. Theholorype's suture has lot beerifigured,.being perhapsnot preserved; in our forms it repeats the characteris-tics of Omoderocerns cantiAnense.-

The specimens figured by Cope (1991 , pl. 3, fig.4; pl. 4, fig. l0) are sliehtly more involute and lessco"isely rib'bed than Brelmei's (196, holorype. Thusthey are more close to our forms, to which theyresemble also for the broad-ribbed ornamentation(mantaining this aspect even at large diameter), fotthe presence of a short inner monospinate stage, andfor ihe indented suture, with very ilor. U lobes (ofwhich U3 is very oblique, nearly perp en&cular to L).

A careful eximination of th'e lharacters possessedby this form lead us to think that they do not corre-spond with those of Epiderocerns (that, by the way,rb.-r to have been subject to various misuttd.trt"td-ings and erroneous interpretations), being rather clos-er to those of Omoderoceras cantianeise, we thusbelieve more suitable to ascribe it to the same genus.

As the tendence from evolute forms to in-voluteones is a common phyletic pattern amongammonites, we can hypothesize that our specimens

(more involute and with an early change in orna-mentation and coiling) may be stratigraphicallyyounger than Bremer's ( 1965) one.

Stratigraphic distribution - Bremer ( I 965, text-fig.5) suppo-sed for his species a location in the basal partof th-e jamesoni Zoie, but without more precise-ref-erences, because his material is erratic. The prove-nance of the exemplars of Cope (1991) it genericallystated as late Sinemurian (Raricostatum Zone)-earlyPliensbachian (Jamesoni Zone).

Genus PnneUICRoDERocERAS Dommergues,Ferretti 6c Meister, 1994

Diagnosis - Mid- to large-sized forms, with evo-lute suF-platicone whorls; olnamentation representedby primary bituberculate ribs and by clear second"ryfin; ribs (striae), which cross the ,r.tttd area from th'eflank. Coiling and ornamentation are kept essentiallyconstant for most part of the growth, with both outerwhorls and body^chamber iharacterized by higherthan wide whorl section (elliptical or sub-rectangular)and flattened ventral area.

The suture is not much different from that ofOmoderoceras.

This genus has been reported chiefly in the upperpart of the late Sinemurian (Raricostatum Zone) of theMediterranean regions (Dommergues et al., 1994a),but it was also- found in thE Austrian UpperAustroalpine (Blau, 1998) and in the SouthernCalcareous Alpr (Dommergues et al., 1997b) in ando-gous biostratigraphic situations. According toFtittebrandt (ZiOzj, earlier Paramicroderoceras iriehtdate back to the Obtusum Zone (base of the [-ateSinemurian). If the attribution of our specimens is cor-rect, later forms are present (even though rare) in thefirst beds of the early Pliensbachian (Jamesoni Zone).

EXPTANATION OF PLATE I

Various specimens of the new subfamily Paramicroderoceratinae (Eoderoceratidae),

Quarry). All specimens are at natural size. A white circle marks the beginning of the bodyFig. li, b, .

^ - Ventral view, lateral view and whorl section of Omotr rottril cantianenti (

Fig. 2 - Laterd and ventral views of Omoderoceras cantianense (pararype, Pa78-E2,Fie. n - Lateral view and whorl section of Omoderoceras cantiaiense (paratype, PaiFiE. 4 - Lateral view and whorl section of an indeterminate Paramicroderoieratin:

of the so-called Apennine " Tbnaspidoceras quadrarmAtum").Fig. 5 Lateral view and *horl section (partially restored) of Omoderoceru$ cf. latiFiE. 6 Laterd view and whorl section of Omoderoceras cf. ktinodosum (Bremer)Fig.7 - Vhorl section and lateral view of Omoderoceras cf. ktinodosum (Bremer) 'Fig. 8 - Lateral view and whorl section of Omoderoceras cf. ktinodosum (Bremer)Fig. 9 - Lateral view and whorl section of Omoderoceras cf. ktinodosum (Bremer) 'Fig. 10 - Vrhorl section and lateral view of an indeterminate Paramicroderoceratin:Fig. I 1 - Vhorl section and lateral view of Omoderoceras cf. ktinodosum (Bremer) rFig. 12 - Lateral view and whorl section of an indeterminate Paramicroderoceratin:Fii. 13 - Lateral view and whorl section of an indeterminate Paramicroderoceratin:Fig. 14 - \7horl section and lateral view of an indeterminate Paramicroderoceratini

E VENTURI, C. NANNARONE, M. BILOTTA, LTASSIC EODEROCERATIDAE AMIV

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372 F. WNTURI, C. NANNARONE, M. BILOTTA

PenervucRoDERocERAS aff SIsPINATUM(Geyer, 1886)

Text-fig.7al-a3; Pl. 2, figt 6, 8a-c

1886 Aegoceras bispinatum GsvzR, p. 27 , pl. 4, figs 4-13.1978 Minoderoceias aff. birchiafus Rosenberg - Vnvruru, p. 109.2001

" ParamicroderocerAs" ancyrense (Bremer) - VPNruru 6(Bu-orrn, p. 328, :ab. 2.

2O0I " Epifurocetras" sp. ind. VnNruru & FEnnr, P. I 27 , pl. 1 l, g.

Material- Eight specimens (mainly fragments).

Measurements (in mm) -

N u m b e r d u h w u / d d h h / d d d

figr 27-29; pl. 4, fig. la-b). The suture is visible onlyoi the large fragmJnrPaTS-829 and, from what canbe made but, it looks like that figured by Gey'er(1886, pl. 4, fig. t3): E is shorter than L; L itself isbifid and has very divergi.g main branches, the outerof which tend to invade tht ventral area; the umbili-cd lobes are rather inclined. The ornamentation ofthis specimen (Text-fig. 7a3;PL.2, fig. 8a;c), remainscoarse even on the Sody chamber, and has closerspines compared to what can be seen on Geyer's(i 836) figuies. On the other hand, all other speci-mens of

-our collection have more distant spines

(Text-fi g. 7 al-a2).

Stratigraphic distribution According to Bremer(1965, p. 1fi), Geyer's (1886) material probablybelongt io the Raricostatum Zone (late Sinemurian).

Genus PnneoERocERAS nov. gen.

Typt species - Parad.eroceras picenum nov. sP.

Name deriuation - From the Greek pard (= near-_by) and Derocerns, origin ary denomination ofEoderocerns.

Typt locality Mount Catria (Umbria-MarcheApennines).

Typit beds - Calcareous-micritic succession of the"Coiniola", with decimetric calcareous beds and mil-limetric clayey joints; early Pliensbachian.

Pa78-E29 -162.4 -59.0Pe78-830 23.0 8.70Pa78-E3l -20.3 -6.20Pa78-E32 -20.2Pe78-E33 -14.0 5.10Pe78-E34 r3.5 4.80Pa,78-835 -13.3Pe78-E36 rr.2 4.30

38.07.006.606.204.905.205.303.80

17.3 -0.368.00 0.386.10 -0.476.00 -0.274.90 0.365.40 0.365.20 -0.354.20 0.38

0.46 -0.23r . r4 0 .300.92 -0.330.97 -0.311.00 -0.35r.04 0.390.98 -0.40l . l l 0 . ' (

-0.1 I0.35

-0.30-0.30-0.350.40

-0.390.38

Remarks and comParisons - For their evolute form,narrow section (as wide as high), their ventral eree,the coarse ribs with two evident rows of sharp spines,the intercdation of lateral striae and the fine ribs onthe ventral aree, our specimens seem quits close toAegoceras bispinatum Geyer, 1886 (pl. 4, figt 4-13),wliich in tuin can be considered the same species (or

nearly so) as Aegoceras Praecursor Geyer, 1886 (pl. 3,

EXPIANATION OF PIATE 2

Various specimens of the new subfamily Paramicroderoceratinae (Eoderoceratidae),

Quarry) and Ful lumachella (Furlo Pass). Unless contrary indications, all specimens are atning of the body chamber.Fig."l $7horl section and lateral view of Parafuroceruts picenum (holoryp e, Pa78-83fii. Z \7horl section and lateral view of Paraderoceruts'picenum (pararj'p e, Pa78-81'Ffi. 3 Lateral view and whorl section of Paraderocents'picenum (-pararyp e, Pe78-E4tFiE 4 Lateral view and whorl section of an indeterminate Paramicroderoceratinae.fi[. I Laterd view and whorl section of an indeterminate Paramicroderoceratinae

the so-cdled Apennine " Tbtaspid.oceras quadrarmAtum"). Phragmocone and body chamb

Provenance: Furlo.Fig. 6 Lateral view and whorl section of Paramiroderoceruu cf . bispinatum (Geyer) (

chamber. Provenance: Pdlareto.Fig.7

Fig. 8a, b, c -

Fig. 9a, b

Fig. 10Fig. 11 -

Fig. 12

V/horl section and lateral view of an indeterminate Paramicroderoceratinae (a new speciesto O. cantianense). Provenance: Pallareto.Bodv chamber *horl section (partially restored), lateral view (fragments of body chamber :-ocbn. whorl secrion (oardally restoied) of Paramicroderoceras cf. bispinatum (Geyer) (Pe7iV/horl secdon, laterd ,ri.* rtrd magnified lateral view (* 2) of an indeterminate Paramicrospond to the inner whorls of the rJ-."ll.d Apennine " Tbtraspid.oceras quadrarmatum"). Phrzclnnot be disdnsuished. Provenance: Furlo.Vhorl section "ild laterd view of an indeterminate Paramicroderoceratinae. Provenance: P:Lateral view and whorl section of an indeterminate Paramicroderoceratinae (perhaps a sPecPhraemocone and bodv chamber cannot be distinguished. Provenance: Furlo.Later?l view and whorl section of an indeterminate"Paramicroderoceratinae (it should corrthe so-called Apennine

" Tetraspidoceras quadrarmatum"). Phragmocone and body chambeProvenance: Furlo.

E VENTURI, C. NANNARONE, M. BILOTTA, LTASSIC EODEROCERATIDAE AI4IV Pl.2

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nI twI t

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374

Material Four different-sized specimens,assigned to the same species, preserved as silicifiedinte"rnal moulds, without trace of the shell (prove-nance: Pallareto Quarry), and two spathic immaturespecimens (provenance: Fu2 lumachella of the FurloPass).

Diagnosis Evolute shell, with sub-trapezoidalwider than high whorl section.

Ventral area not much rised, ranging from slight-lv roof-like (in the inner and middle whorls) toiounded (at larger diameter, includitg the bodychamber).

The ornamentation, which mantains its aspecteven on the body chamber, is made of quite broadprimary ribs ioining two rows of spines (umbilicaland 'n.tttro-laferal) "]ita by finer and lloser second aryribs which, from the ventro-lateral edges, cross theventral area without interruption. The spines seemdirected obliquely to the coilins plane of the shell: theventro-lateral ott.r upwards,- ihe umbilical ones(apparendy shorter arid smaller) downwards. Thesmill specimens from the Fu2 lumachella show thatthe inner whorls are smooth until a variable diameterberwee n 4 and 7 millimetres, and then the broad riha-aPPear.- -The

suture is moderately indented, with arbores-cent lobes rypical of the subfamilv 6ut a little short-er than thoie of Omoderoceras): E ne arly as long as L(which do not seem to have an accentuated tendenceto invade the ventral area); inclined umbilical lobes,with U3 nearly perpendicular to L and approachingvery close to ths outer branch of L itselfi, closing U2on the boftom.

Remarks - \fith the few available specimens, weare not able to give an exhaustive appraisal of the vari-abiliry of Pariderocerns. However, its verJr peculiaraspect allows a quite easy differentiation from otherbispinate forms.

^Only *h.tt other ammonites safely

"rrisn"ble to this g.trr will be discovered, it will b;porlible a comple6 definition of its variabiliry range.

Included species Paraderocerls picenum nov. sp.(rype species by original designation).

PnneoERocERAS PICENUM nov. sp.Text-figs. 5a-d; 6a-c; Pl. 2, figt l-3

2001 " Epideroceras" sp. ind. VeNruru & Fenm, p. I 27 , pl. I 1, l.

Name deriuation - From Piceni, ancient popula-tion inhabiting the present-day Marche region.

Holotype - Pa78-838, specimen with part of thebody chimber (Text-fig. 5a; 6a-c; Pl. 2, fig. l),housed in the Earth Sciences Department, Universitldegli Studi di Perugia.

E VENTURI, C. NANNARONE, M. BILOTTA

Paratypes - Pa78-E37 , specimen with more than awhorl ofbody chamber (Text-fig. 5c-d; Pl. 2, fig. 2)and Pa78-E40, specimen with t"he beginnitg oI thebody chamber (Tbxt-fig. 5b; Pl. 2, fi;. 3);5oth arehoused in the Earth Sciences Department, Universit).degli Studi di Perugia.

Typt locality - As for the genus.

Typit section Pallareto Quarry bed "Venturi'78" .

Material - Four different-si zed specimens, includ-irg the holorype.

Measurements (in mm) -

N u m b e r d u h w u / d w / h h / d d d

Pe78-E37 68.2Pa78-E38 45.5Pe78-839 37.2Pa78-840 29.0

35.9 r4.0 13.0 0.53 0.93 0.2r 0.1923.6 l r .9 r2.0 0.52 I .01 0.26 0.2614.6 r2.0 l 1 .0 0.39 0.92 0.32 0.3013.7 8.00 7.20 0.47 0.90 0.28 0.25

ESt-l

ESt-t LSl

1-l

b

LS1- LSl|-]

Text-fig . 5 - Paraderoceruts picenum sutures, showing the charac-ters of this n6w genus (all magnified about x 4); e)holorype (Pa78lE38), drawi ar e diameter ofaboui 34 ^ ; b) pararype (Pa78-E 40), drawn at adiameter of aboui 22 mm, c, d) pararype (Pa78-E37; respectively drawn at a diameter ofabout 40mm and 20 mm) (drawing by F. Venturi).

LASSrc EODEROCERATIDAE AALMONITES FROM THE APENNINES 375

Text-fig . 6 - Holorype of ParaderoceruLt picenum (Pa78-E38); a)lateral rrie*; b) section of the last whorl; c) sectionof the last whorl with restored spines, to show theirlength and inclination; natural^size (drawing by F.Venturi).

Diagnosis - As for the genus.

Remarks and comparisons - The peculiar charactercombination explained in the diagnosis_ give_s toParaderoceras a very well distinct "rp.".t and,

"as far as

we can ascertain, tliere are only few Lomparable formsin the literature. The species called bV Bremer ( 1 965)Crucilobiceras Phry7iti* (a generic'attribution thatseems to us nol much accurate, as this form does notshare many characters with the generotyP€ ofCrucihbiceras Buckman), shows some resemblancewith Paraderoceras for its flattened shell with evolutecoiling. However, contrary to the case of our materi-al, th; ornamentation hai more projecting and lessbroad ribs, on which the spines connection are notmuch visible, and in which-the second row of spinesis more close to the umbilical edge. On the ventralarea the second ary ribs are apparently missing (nor

they are mentioned; but it may be a lack in the Preser-vation), the whorl section is more narro% never roof-like, and the whorl development is different; thesuture and the stratigraphic reference are unkno'wn.

The specimen dJsignated by Cope ( l99l; pl. 4,fig. I I ) ai Uptonia sp. ii nearly identital to the abone-m"enrioned Bremer'; ( 196, Crucilobiceras Phrygictlm,and thus is somehow comparable wirh Paraderocerastoo. This early Pliensbachian form is said to be aworn out and perhaps deformed specimen, but to us(judging ftg- th. photograph) i,ts prgservation seemsqgite fine. 4"n"ay, one cannot dgly its stroftg resem-blance to the holorype of Crucilobiceras P4rygitxtm.Considerations of the same kind also aPply to theammonite (probably of early Pliensbachian age)called by Cope (199 l; pl. 4, Frg. 12) Coeloderocernsponticum (Pi;), but its- similariry to Crucilobiceras'phrygicum

and Paraderocerns is less marked.' The specimens figured by Alkaya & Meister

(1995, pl. 8, figt l, T6) as EoderocerAs tardtcrescens(Pia) , local ised as lower Brevispina Zone or

Polymorphus/Brevispina Zone, seem to have someelementi in common with Parad,eroceras (rather thanEoderoceras) for suture, coiling and rib sryte.

'We can-

not say anithing more, because the whorl section isnot figured, thetnly drawn suture is incomplete, andalmosi all the specimens are deformed. Conce_rningthe biostratigraphic position that Alkaya 6C Meister(1995) "ssigied to th.t. clearly bispinate' so-called" Eod.eroceri tardecrescens" , it must be noted that, in

the Apennines, similar forms never occur in the bedsabove the

" T quadrarmntum" Zone (corresponding

more or less to the Thylori Subzone).

Stratigraphic distribution Early Pliensbachian(basal part of the

" T quadrarmAtrtm" Zone).

THN UNCLASSIFIED FORMS

The strons morpholoeical variabiliry noticed inthe Eodero..t?tidae^from"the Pallareto made impos-sible the identification (at least, at a species level) of27 specimens (Pl. l, figs 4, 10, 12-14; Pl. 2, \gs 4r7 ,l0).^'We cannot excludl that, among this unclissifiedmaterial, new til€ might be reco gnlzgd in the future.As an example, two sriall individuals have very btogdwhorl and ironospinate inner stage (Text-fi g..7b; Pl.I , fig. 4), closely resembling nvo other untlassifiednuclEi from the irul lumachella of the Furlo Pass (Pl.

2, figt 5, 9a-b, l2): all of them probably must beascribed to a new species of Omoderocerns. As previ-ously said, these foims should indeed.fPresent alsothe

'inner whorls of the Apennine

" Tetraspid'oceras

quad,rarmatum" (not visible bn the specimen figuredin Faraoni et al., 1996) that, moreover, show evidentParamicroderoceratinae characters (e.g. the ornamen-tation sryle).

The suture of the unclassified specimens hasalways the same basic characteristics, diagnostic forthe subfamilv Paramicroderoceratinae, *Jrereas thecoiling,. the whorl width and the details of the orna-mentation show a considerable morphologic

"mal-

leabiliry". Besides some rather evolute-and persistent-ly bispinate forms, or that in any case loose later their

#itt.i (features that can be considered plesiomor-phic), there are others in which three innovative char-icters simultaneously appear (features that are com-pletely established it i6. Eoderoceratoidea of thesubsequent parts of the early and middlePliensbachian):

I ) tendence to whorl widening;2) tendence to increase in involution;

. 3) early loss of a toy of spines (presence of thelnner monospinate stage).

Among th.t. formsl four quite involute sPecimenslikely belSng to a species oF Omoderocerai perhapsclose to O. iantianeise (Text-fi g. 4c; Pl. 2, figs 4,, 7).

Some specimens, either involute or evolure, Tigh:somenmes have lateral secondary ribs (or intercalatedstriae) (Pl. I , f igt 10, 12-14), bui this does not neces-

376 E VENTURI, C. NANNARONE, M. BILOTTA

sarily imply that they must be ascribed to the genusParimit-itrocerus. A dready stated above (also inthe diagnosis), we believe that is advisable to limit theuse of tlis name to a more restricted range, comparedto that normally admitted in the_ Past. Such amethodolopy, which prefers the use of riell-character-ized and deTimited taxa, induced us to caution in thesystematic designations. This is the main reason wechoose not to give a specific ("t times nor generic)assignment to ammonltes unprovided of all the diag-trorii. features of safely t.iogttizable forms. As;whole, they are specimens widi

"intermediate" char-

acters between those of the individuals that we haveidentified as rypical for the genera Paramicrod,eroceras,Omoderoceras

-and Parad,erocerasi because in our

palaeogeographic area a sufficient record of faunas^prec.dltrg" "ttd subsequent to bed

"Venturi '78"

(which aitually seems to be a yet isolated event) islacking, it is impossible to understand the phyloge-netic ind taxonomic meaning of the variabiliry hereobserved.

DrscussloN oN THE AFFINITIES

All the Paramicrod,eroceras, Paraderoceras,OmoderocerAs as well as the unclassified forms comingfrom bed

"Venturi '78" of the Pallareto share the

stratigraphic position, the,ftthyan, geographic Prove-nance and several morphologic and structural charac-teristics (see the above-t.poited diagnoses). This ledus to ascribe them to the same subfamilyParamicroderoceratinae. Mainly on the basis of theinner whorl development of these genera and on thecharacters of their ornamentation during ontogenesis,we think that the

"ancestral" form of ihe t,tbf"-ily

might be ParamiroderocerAs: it has actually many ple-siomorphic features, such as the greater evolution andthe perrnanence of spines; moreover it has the earliestrecord, being alr^eady present from the lateSinemurian. 6n the oih.f hand, Parad,eroceras andOmoderocerAs are to be considered as

"derived" forms(especially the latter, having marked innovative ten-dences).

In our opinion, no further already-known taxacan be ascribed to this new group. For instance,Microderoceras Hyatt is often coitidired a close rela-tive of Paramicroderoceras (Dommergues 6( Meister,1999; Hillebrandt, 2002), but it shows some charac-ters (concerning chiefly the suture and the geograph-ic-stratigraphic distribution) that lead us to exclude itfrom thE Piramicroderoceratinae. At the moment, webelieve that it must be placed it in a different sub-family (see below).

A-systematic revision of all the Eoderoceratoidea isbeyond the aim of this work, and we cannot exhaus-tively appraise many classification hypotheses.*prLs.d' by various Authors (fot

' inrt"nce

Dommergues 6( Meister, 1999). Nevertheless, wewould like to propose a rough hierarchical arrange-

ment for the first group of this superfamily and itsmain genera, basing on our data:

Superfamily EooEnocERAToIDEA Spath, 1929^Family iiooERocERArtDAE Spath, 1929

lribbed forms with one or two rows of spines,sometimes with the tendence to spoliation duringthe growth, or, as hiehlv derived condition, par-tialli spoliated (only-ribbed); secondary ribs that,m,rilli cross without interruption the ventralarea; lntercalated small lateral iibt are often pre-sent; suture more or less indented, with more orless arborescent L, essentially bifid].

Subfamily EoDERocERATINAE Spath, 1929

fBoreal Sinemurian-early Pliensbachian forms;with one or two rows of spines, more or lesspermanent; relatively simple suture, with E aslotg as L, that lacks'" t "r^to'w

"trunk"].

Genera: Eod.eroceras Spath, XipherocertsBuckman, Microderoceris Hyatt, BifericerasBuckman, etc.

Subfamily PnnevtcRoDERocERATINAE nov.

[Tethyan- late Sinemurian- early Pliensbachianforms; bispinate without lppreciable ontoge-netic variations, or monospinate with tendenceto spoliation during the growth (monospinatelnner stage; subseq,Lttt lo-ss of spines and ribs);sutures #ith E always shorter than L, whichhas a narrow

"trunk" and the outer branch

often tending to invade the ventral area;inclined umbTlical lobes; broad ES and LS Isaddles].

Genera: Paramicrod.erocer*s Dommergues,Ferretti 6( Meister, ParaderocerAs rlov.,Omoderocerns llov.; + other forms erro-neously ascribed in the past toTbtraspidoceras.

Subfamily EIIDERocERATINaE Dommergues &Meister, 1999 (nom. transl. nov, ex Epide-roceratidae Dommergues 6c Meister, 1999)

[Sub-boreal and/Jr Sub-Tethyan lateSinemurian-early Pliensbachian forms;bispinate with tendence to spoliation duringthe'growth, or partially spoliated (only ribbeflisubiriangular bgival ieciion in the adult bodychamb.tih. suture seems known only for thefirst three genera (the remainitg two are there-fore included in this group with reservation,indicated by the qn.tiiorr^rn"rk), and has Egenerally quite as fong as L or a little less, Liuittt a narrow

"trunkt and the outer branch

that never seem to invade the ventral area].Genera: Epiderocerns Spath, CoeloderocerasSpath , Pseuduptonia Bremer, ??Pseudoohricodoceias Dommergues,Moute?de 6( Rocha; ? Capreoliceras Alkay"& Meister.

Subfamily CoELocERATINAE Haug, 1910

[Boreal and lor Tethyan late Sinemurian-

LUSSrc EODEROCERATIDAE AMMONITES FROM THE APENNINES 377

weakening and subsequent more or less gomplete lossof ornamentation wasa peramorphic variation. It wasnormally realized with the transition from the ribbedbispinate stage of the inner and middle whorls to theribbed o, ,--ooth stage of the outer whorls (this h"P-pens, for instance, ii Epideroceras). On the contraryitt the Eoderoceratidie assignable to the earlyPliensbachian (bed "Ventu

ri'78" and Ful lumachel-l"), a ribbed bispinate phase (if present) involves onlythe middle whbrls, frbm which the transition to anon-ornate phase (ribbed or smooth) is rather Preco-cious. Moreover, as can be seen in some smallParamicroderoceratinae nuclei from the Pallareto, astage without ribs is present also in the innermostpait of the whorl (Text-fig. 7 cl-c3). In few speci-hens, between this phase and the ribbed bispinateone of the middle whorls, it occurs a stage at firstmonospinate without ribs, then ribbed monospinate(Text-fig. 7b). This leads to think that the spoliationof theselndividuals is actually a paedomorPhosis, pre-luding a complete establishment of the monospinatecharaiter in- other early Pliensbachian Eodero-ceratoidea (Caleites Venturi 6( Ferri, MiltocerAsViedenmayer and some still unpublished Mediter-ranean to"). Therefore, the losi of spines, besidesbeing an ontogenetic variation of the individual orna-mentatlon, iriplies also an evolutive modification,progressively developed within the superfamily dur-irg"the

" Teiraspidociras quadrarmatumr' Zone.

Pliensbachian forms; with a single row ofspines (medial or ventrolateral); suture with Elonger than L, U2 lobe more develoPed thanU3: oblique ES saddlel.

Geneia: Coeloceras Hyatt, Apod.erocerasBuckman, Hyperderocerus Spath, MiltocerasViedenmayei, Metad.eroceras Spath,Dubaricerts Dommergues, Mouterde 6(Rivas, etc.

In our opinion, the family Eoderoceratidae is arather homogeneous group, being well separatedfrom the othe"r ta>(a ofihe o-. ."tik ascribed to theEoderoceratoidea (Polymorphitidae, Liparoceratidae,Dacrylioceratidae). As'it can be observed, the divisionin subfamilies is operated on the basis of all the avail-able elements: morphologic (shell shape and orna-mentation), structural (Iutural features), biogeo-graphic and stratigraphic distribution.

THr, SPoLIATIoN

One of the most interesting features possessed bymost of the Eoderoceratidae itudied in the Presentpaper is their innovative manner of spoliation. This isI ttitt not completely known paffern, which started atleast from the^late Sitt.-uriin, and is accomplishedthrough different times and ways (Venturi, 1999).

In"late Sinemurian forms of the same family, the

@iffial

-\rirrr

I

{4fr@a*(fficl W/

c2

s2

rext- n g 7 - 3i1ft"il*l'r:t$'i,:::*'T,'l'fr:::ton specimens from the Pallareto Q.*"tt1tNeai each individual in lateral view isplaced its whorl section. al0-a3) onto-qenetic development of Paramicro-

(;r:rn:';^3::!i{;i':#,^S:{;i};":stil l present it large diameter (al:nucleus Pa78-E34, viith originary dia-rnerer = 13.5 mm; a2: young sPecimenPa78-830, with originary diameter = 23mm; a3: adult with[ody chambe r Pa78'829, originary diameter = about 160mm); b)"unclissified immature (proba-blv belonging to a new species ofOmoderoceiaii that should correspondto the inner whorls of the so-calledApennine

"TbtrAspidoceras quadrarmt-tim" (and perhapi also to thot. of

" T

quadrarmntum" sensu Dommergues E{Meister, l99l); note the init ial mono-spinate stage without ribs, on smoothwhorls; ma[nified x 2 (originary diame-rer = 9 mm); cl-c2-c3) onrogenericdevelopment of Omoderoceras cf.

- latino-

dosum (Bremer), showing its various sta-ges, unti l the spol iated Enal phase (cl:iucleus magnif ied x 6. rvi th'orieinarydiameter = I mm; c2: \ 'oung specimenmagnified x 2, with originan'-dii-.re r_=8 mm; c3: adul t x l ) (draw' ing bv F.Ventur i ) .

378 F. VENTURI, C. NANNARONE, M. BILOTA

Comparing late Sinemurian forms with.. earlyPliensb".hi"tt"on.r, it can be observed that spoliationis accompained by an increase in whorl width and

coiling: be.ing " phyletic *"tge,invol"iTq ma,nI char-

acters-at the same tlme, it can be considered a mor-phologic covariation (term here used in a broader-."trihs than in Guex,200l). This phenomenon, as

in part "already

noted by Bremer (196r' concerned*aitrly the -ot. involute Eoderoceratidae (for

instan'ce Omod.eroceras, Epiderocerns and Pseuduptonia

Bremer), which have ribbed (and normally spined),

relatively less coiled inne r andlor middle whorls, and

compleiely (or nearly) loose their ornamentation in

o,rt.i whorls. The evolute taxa, instead' mantain

throughout their growth Permanent or semi-perma-nent sprnoslty an4 degree of coi l ing (e.g.

Paramicro dero cerAs and ParaderocerAs) .The causes leading to spoliation are unknown, but

we can observe that-this pattern is only one of the

numerous modifications that the ammonite fauna

underwent during the Sinemurian-Pliensbachiantransition. Its final"phase is contemPoraneous to the

adaptive radiation of the Polymoiphitidae, which,t"rt.d from the base of the Pliensbichian and con-

tinued for most part of the early Pliensbachian. Even

though the complete understanding of. the spines'funct-ions is a field oPen to sPeculations (Donovan et

dl., 198 I ), these str^uctures can be interpreted as apassive defence system, but they can be important in

helping the sheil stabiliry too.'Therefore the loss of

spines Trr"v also depend from variations in the ethol-

iW and/or in the hydrodynamic requirements of the

"fri-"l. Considering that forms such as Omoderoceraswere not particuhlly adapted to active swimmiTg,then this morpho-functional changg may be an index

of palaeoenvironmental alterations (Venturi, 1999).tnit suggests the hypothesis that the loss of orna-

mentation "i"'n

the Eodiroceratoidea and the faunal

chanse of the Sinemurian-Pliensbachian transitionmigh"t have at least some causes in common. The

ren"ewal observed in ammonite assemblages, in fact,

corresponds to stable isotope variations (positive for

a''O, hegative for a"C)- "tt{ also to evolutive and/or

extinctio"n epsiodes of calcareous nannoplanktonrecorded in tn. same time interval (Mattioli et Al.,

2003). In particular, the negative D''C shift, accord-

i"g to the ggqera.lly accepted interpretations of simi-

lar cases, mtght tmply a decrease ln water temPera-tures: perhap-s this iould be related to seaway open-ings,(it more.in general, change in the palaeogeo-griphic seffing).

THE SINEMURTAN-PLIENSBACHTAN BOUNDARY

THE GSSP CORRELATION POTENTTAL

The stratotype (GSSP) for the Sinemurian-Pliensbachian bound tA, recently recommended for

the \f ine Haven section (Robin Hood's B"y,

Yorkshire, England), completely agrees with the

already-mentio.'ned standatd d.finitioi of the _begin-ning of the Jameso ni Zone (Thylori Subzone). In fact,

thetr"r. of ihe Bifericeras d,onouani horizon (bed 73b)is considered th. beginnitg of the Pliensbachianbecause it contains ^i epod4rocerns sP. jtt ; further-more, it overlies the last Upper SinemurianEchioceratidae, and precedes the first classic Lower

Pliensbachian ApodeVoceras and Phricod,ceras taylo1i(Dommergues & Meister, 1992; Hesselbo et 41.,

2000; Meister et a1.,2003).The conventional criterion (presence of

Aooderocerus and/or Tbtraspid'oceras quad'rarmatum) it

uiually accepted, also for traditionil reasons' as the

only bio.rr.ttt ptoviding an indication for the begin-

nins of the Pli6nsbachiin. At present, it allows to rec-

oguirrc the actual base of the Thylori Subzone only in

tli.'Wine Haven section: this biostratigraphic datumcannot be used apPropriately in other known out-

crops (neither Boreal, nor 'belonging

19 different"reas) (Meist er et al., 2003). Anyw iy, trf this -providesa good reference for Boreal and Sub-boreal regions

G.[orth-\7est Europe), we think that the same is not

true for the Tethyan ones (Itafy, Morocco, Tunisia,Albania, etc.). Here, in fact, the standard biostrati-

eraphic principles that charac terize the middle Lias(.rp..ially its beginning) are inapplicable..Thus, in

ih.r. "r."r, the 5i..-u-rian-Pliensbachian bound ery

cannor be precisely determinated. The fauna of the

bed 73b ofVine Haven, recommended as world ref-

erence for the biostratigraphic recognition of the

basal Pliensbachian, is m-ade of nume-rous Bifericeras

d.onouani Dommergues & Meister, a few Gleuiceras

iuv. aff . iridesceis (Tutcher 6( Trueman), xr'Apod,erocerus sp. jtt and, accordilg to Howarth

QOOZ), also ah A. subtriangulare. In our opinion,none of these til(a (neither sEparately nor as associa-

tion) seem to offer a good correlation potential for

extra-Boreal areas. In" fact, Bifericeras d.onouani is

strictly endemic to \7ine Haven (il hT never beenfound elsewhere) and Gleaiceras is also known in the

late Sinemurian. So, Apoderoceras is the only signifi-

cant enough form, buf it seems comPletely absent in

most part of the Tethyan localities, and the same

happehs for Tbtraspid.oiqras quqdrarmAtum (Brag? et

at. ', igg(; El Harif i et dl., 1996; Lachkar et dl., 1998;

Dommergues et dl., 2000). In the Apeqnines, as

already ,{id, true T quadra.rmatum are lacking, andthe ottly known representative of Apodgroc.eras comesfrom the Ful lumichella, which seemingly is subse-quent to the bed

"Venturi'78" (that is, to an unques-tionably renewed fauna, compared to rypical late

Sinemurian assemblages)\We believe that a GSSB to have a world true use-

fulness, must at first (not to neglect other crtiteria)allow sufficiently reliable correlltions for as many

areas as possible,'and not onh for a single P"l.agogeq-graphic domain. The'Wine Haven secdon' dthg.tph

possessing many of the necess ary requirements to be

LUSYC EODEROCERATIDAE AMMONITES FROM THE APENNINES 379

a GSSP. (good exposure and accessibiliry sedimenta-

ry conunuiry, fosiil abundance, etc.), dbes not seemto assure with acceptable confidence the expectedcorrelation potential (at least, with a resolutionbeyond the Subzone scale) outside the Borealdomain. Due also to the great sedimentary differ-ences (both qualitative and of thickness) that con-tribute to mike so hard any comparison betweenBoreal and Tethyan successions, we think that a stra-torype for the Sinemurian-Pliensbachian bound a\ybased on Apod,eroceras and Bifericeras d.onouani mighthave, at the present state of knowledge, x palaeogEo-graphic value limited merely to the Boreal domain,I"d thus a too restricted significance.

All these reasons were Explained in detail to thePliensbachian'Working Group during the voting ses-sion on the GSSP proposal for the'Wine Haven sec-tion (with complete results in Meister et al., 2003, p.276), and motivated our abstain.'W'e

believe that there is a strong need for morebiostratigraphic studies, especially in extra-Borealareas, to t.r? the real applic"biliry of the Sinemurian-Pliensbachian bound ary concept used at

'$fine

Haven, thus confirming or denying its practical effec-tiveness as GSSP. As a

"-"tt.r of fIct, the ratification

of this bound ary stratotype before such studies,mieht formallv not allow a safe recognition of thebefinnirg of the Pfiensbachian in the Intire Tethys.

THp Eenrv PIInNSBACHIAN IN THE ApENNINES

The impossibiliry to apply in the Tethyan regionsthe biostratigraphic criteria used in the North-'WestEurope to dEteimine the base of the Pliensbachian,does hot eliminate the need to reco gnize with appro-priate accuracy the possible presence of fossils refer-^"Ut.

to this time inte^rval in ottt areas. 'We

can sdll fol-low the historical definition of the Sinemurian-Pliensbachian bound "tft which implies for theammonites a elobal faunal change, with disappear-ance of the Ejhioceratidae and rilbr.quent diversifi-cation of the Eoderoceratoidea, but we must base ondifferent genera and species.

In th6 Apenninei, the first assemblage corre-spondirg to these features is r€presented by theCatriceras catriensebioevent (bed "Venturi'78"

of thePallareto Quarry), and partially also by the bed 39 ofthe Bosso section, which is more or less equivalent toi t .

As alre ady reported by Venturi & Ferri (2001), theApennine associations which overlie the lastEihioceratidae of the late Sinemurian (PaltechiocerasBuckman, Plesechioceras Ti"ueman 6( \Tilliams), doshow a substantial renewal. They are characterizedbythe concomitant first occurrence of Galaticeras (massappearance) , Radstockiceras Buckmxr, Polymor-phitidae (small, smooth forms without a keel, evoluteor passing from involute to evolute) and above allCatr icerAs (morphological lv variable Tropido-

ceratinae, more or less lenticular, keeled and withoutspines). Contemporaneous to these appearances, thefinal phase of the spoliation of the Eoderoceratidaetakes place.

The bed "Venturi '78"

contains exacdy all thejust-mentioned elements, with taxa characterized bymarked polymorphism and high diversiry whichhave p"rrbd ih.o,tgh many (and 5ft.tr rapid) changesover ihe time: Catriceras catriense (Thopidoceratinae),Furlites (smooth Polymorphitidae), numerous speci-mens of Galaticeras, Eoderoceratidae with tendenceto spoliation (Omod.eroceras), Orynoceratidae (fourRaditockiceras and a Gleuiceras Buckman). The rareParamicrod.erocerls and two interesting unpublishedammonites similar rc Asterocer*s Hyatt or RipariocerasSchindewolf are probably to be interpreted as lateSinemurian

"leftovers", ".td perhaps they may testi$/

a not yet complete faunal change. However, theabsolutl predominance of formf which are notrecorded in the Raricostatum Zone (being further-more significandy

"new"), suggests to consider the

bed "Venturi'78"

as the first post-Sinemurian assem-blaee of the Apennines, also because it seems to pre-cedi the more openly Pliensbachian fauna of the Fu Ilumachella.

It is interesting to observe that in Morocco,Tunisia, Albania, ind partially also in Turkey, thebiostratigraphic data for the early Pliensbachian seemto be qni"'t. "tit . to the Apennine ones, but they comefrom generally more incomplete sections, and some-times ih.y were apparently underestimated. This hap-pened, for instance, in the Jebel-Bou-Hamid section(Morocco), where the presence of Galaticeras in thefinal part of a very thick Sinemurian succession(Lachkar et dl., 1 998), was not considered a safePliensbachian bioevent, because the Authors did notexclude (quite inexplicably) the occurrence of thisgenus in th. late Sinemurian (a fact, by now neverdo..t-ented). Considerations of the same kind applyto the Turkey (Asaei Gokdere section), where aRadstockicerai sp. bioenent, found between aPabechioceras romanicum horizon and a Pseuduptoniamicromphala one, was not deemed to represent thebase of'the Pliensbachian (Alkaya & Meist-er, 1995, p.165). In this case, however, the caution is justified,because the first occurrence of Radstockiceras,although often considered a marker for the beginnitgof the Pliensbachian (..g. Meister 6( Sciau, 1988;Venturi & Ferri, 2001), is also reported in the latestSinemurian (Donovan et al., 1981 ; Donovan, 1994:Dommergues et al., 1994a, 2000).

In th? Djebel Oust-Est condensed secrion(Tunisia) a Pliensbachian layer containing GalaticerAsand Tbtraspidoceras is registered (Rak(s 6{ Guex,,2002): it might be referable to the faunas characteriz-ing of our

"T qradrarmatum" Zone, but is assigned,

pr6UrUly in.ori.ctlv, to a later biostratigraphic i-nter-val (Aenigmaticum/Demonense Zones).

Converselv. in more distant areas, there seems to

380 E VENTURI, C. NANNARONE, M, BILOTTA

exist the premises for a good biocorrelation with theApennines: in Argentina, (Arroyo Las Chilcas sec-tion) is reported a Catriceras bioevent, correcdyplaced after the Paltechioceras and before theMihoceras ones (Hillebrandt, 1990, 2002, and per-sonal communication).

In all the above-mentioned sections the Borealtaxa which provide an indication for the earlyPliensbachian are absent, and vice versa, the firstApennine forms which can be considered as post-Sinemurian (chiefly Catriceras and Furlites, but alsotrue Gakticeran, have never been found in the Borealdomain. Obviously, it is not our intention to proposethe fauna of the Md

"Ventu ri'78" as a global^marker

for the base of the early Pliensbachian,.'b..",rr. (as awhole) it is unknown elsewhere, not even in otherparts of Italy: this is reasonably due also to the con-siderable faunal and/or sedimentary differences exist-irg among the various Tethyan areas. Nevertheless,the renewal represented by this bioevent must warnus on the ratification of a GSSP for the Sinemurian-Pliensbachian bound tA, because it demonstrates thescarcity of knowledges concerning this time interval,and the impossibili-ty to establisF for it careful andreliable global correlations.

CONCLUSIONS

The high morphologic variabiliry of the Eodero-ceratidae studied in the present work is a good exam-ple of the polymorphism showed by am--monites inthe Umbria-Marche Apennines at the beginnirg ofthe early Pliensbachian. This is perhaps "'-ore gen-eral condition, which can occur also^ in other ir."twith similar situations. The abundance of ecolosicalniches, and the consequent great diversificatioil ofammonite assemblages (.rp..iilly in Teth yan areas, asnoted Uy f-i,tt, 1986), is settled within a generalizedtransgresslve phase, and seems to be facilitlted by the

t iassic displacement of the great carbonatic plat-forms. AIso linked to this, is ln increased develop-ment of the provincialism, which in Pliensbachian-isstrongly marked than during Sinemurian or Toarciantimes (Meister 6c Stampfli, 2000). The already-notedbiocorrelation difficulty berween Boreil andMediterranean successions perhaps may depend alsoon this set of palaeogeogriphic

^and palaebecologic

factors.Our data suggest that the Apennine faunas are rel-

atively isolate (i.e. endemic) not only compared to thefarthermost part of western Tethys (Mbrocco andSouthern Spain), but probably even more in regardsto the South-eastern (Arabia, Madagascar and India)and North-eastern ones (Himalaya ind Karakorum).It is now widely accepted that the Apennine portionof the Tethys was a sea placed "t tropical palaeolati-tudes, with'*"t-, life-riih warers "rd diveisified sea-bottom. From an essentially speculative point of view,this fact lead us to imagine th"t its complex ecologic

systems and htgh. competition might lt"y. providedmany favourable incentives for the evolutive process-es, making it a true

"biologic forge" (or a somehow

privileged area for this aspect). It is certainly risky tostate unconditionally that the Apennines were a

"cen-

tre of origin" for.,.b. ammonites, also because thisconcept is too difficult to appraise, and surely israther disputed. However, we believe that the prob-lem of the origin of the til(a is a sdll important itudyfield, and it ca-nnot be ignored. For instance, the greatdiversification of the Alennine forrns, includi"f theearliest Tiopidoceratinie (Catriceras) and smiothPolymorphitidae (Furlites) ever recorded, might beinterpreted as a sign of their native origin (or-nearlyso). However, the objective support for this conjec-ture is scarce: between Catriceias and its supposedEoderoceratidae ancestors there is a tremendous mor-phologic gap, neither are known transitional forms,nor reasonable direct forerunners. There are indeedmany motivations that one can adduce: lack infoundirg the forms, outcrop absence, immigration ofextra-Apennine til(a (helped also by the changedpalaeogeographic sefting), etc. Clearly, these are ohlyhypotheses suggested by ^ few data, that serve as anincentive for further and more accurate studies.

The fauna of the bed "Venturi '78"

is importantto characteri ze in the Apennines the renewal associat-ed with the Sinemurian-Pliensbachian boundaryiunfortunately, its taxa are different from those presentin the Boreal domain (including the \Vine -Haven

GSSP), and perhaps *r":y reflec-t, palaeogeographicisolation as well as different palaeoenvironmentalconditions. Many points are still left open in theApennines: the presence of beds lacking fossils (for atleast l0- I 5 m) in the Bosso river iection makesimpossible to define a precise bound ary at the transi-tion between late Sinemurian and early Pliensbachianfaunas. Only with further researches in the Tethyansuccessions it will be possible to solve the problem,clarifyirg its various implications. For this reason, w€intend to publish as soon as possible the results of astudy on the Pliensbachian faunas from the FurloPass (Fu I , Fu2 and Fu3 lumachellas), repeatedlymentioned in the present paper.

AcTNovlEDGMENTS

'We would like to thank: G. Lucarini, who took the pho-

tographs of the specimens presented in rhe plates of this paper; P.Faiaoni and A. Marini for some unpublished biostratjgiaphicdata on the Bosso section; G.C. Pozzi for her hints conlerningthe plates; G. Rea, who gave us mosr part of the marerial herEwidily used; F. Cecca and C. Meirter *ho reviewed the manu-script and helped us to greatly improve it with their suggestionsan(l correcuons.

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(manusript receiued July 29, 2003accepted March 8, 2004)

Federico VpNruruCarlo NnNNnRoNE

Massimiliano Btl-orrn

Dipartimento di Scienze della TerraUniversit) degli Studi di Perugia

Piazza Universit) I , 06123 Perugia, Itdy