late cretaceous nodosaurids (ankylosauria: ornithischia - scielo

Late Cretaceous nodosaurids (Ankylosauria: Ornithischia) from Mexico 371

ABSTRACT

Nodosaurid ankylosaur remains from the Upper Cretaceous of Mexico are summarized. The specimens are from the El Gallo Formation of Baja California, the Pen and Aguja Formations of northwestern Coahuila, and the Cerro del Pueblo Formation of southeast Coahuila, Mexico. These specimens show differences from other known nodosaurids, including an ulna with a well developed olecranon and prominent humeral notch, the distal end of the femur not flaring to the extent seen in other nodosaurids, and a horn-like spine with vascular grooves on one side. The specimens represent the southernmost occurrences of nodosaur remains in North America, and provide an important biogeographical link between nodosaurids of the United States and Canada on the one hand, and Argentina and Antarctica on the other.

Key words: nodosaurid, Ankylosauria, Late Cretaceous, Baja California, Coahuila, Mexico.

RESUMEN

Restos de anquilosaurios nodosáuridos del Cretácico Superior de México son descritos aquí. Las muestras proceden de la Formación El Gallo de Baja California, de las formaciones Pen y Aguja del noroeste de Coahuila, y de la Formación Cerro del Pueblo, sureste de Coahuila, México. Estas muestras presentaron diferencias significativas con otros nodosáuridos conocidos, incluyendo el cúbito con olécranon bien desarrollado y la muesca del húmero prominente, el extremo distal del fémur de diferente medida no visto en otros nodosáuridos, y una espina similar a un cuerno con los surcos vasculares en un lado. Las muestras son importantes porque son los hallazgos más meridionales de América del Norte, y proporcionan un vínculo biogeográfico importante entre los nodosáuridos de los Estados Unidos y Canadá, por un lado, y Argentina y la Antártida por el otro.

Palabras clave: nodosáurido, Anquilosaurio, Cretácico Tardío, Baja California, Coahuila, México.

LateCretaceousnodosaurids(Ankylosauria:Ornithischia)fromMexico

Héctor E. Rivera-Sylva1,*, Kenneth Carpenter2,3, and Francisco Javier Aranda-Manteca4

1 Departamento de Paleontología, Museo del Desierto, Carlos Abedrop Dávila 3745, 25022, Saltillo, Coahuila, Mexico.

2 Prehistoric Museum, Utah State University – College of Eastern Utah, 155 East main Street, Price, 84501 Utah, USA. 3 University of Colorado Museum, 80309 Boulder, Colorado, USA.

4 Laboratorio de Paleontología, Facultad de Ciencias Marinas, Universidad Autónoma de Baja California, Ensenada, Baja California, Mexico.

* [email protected]

Revista Mexicana de Ciencias Geológicas, v. 28, núm. 3, 2011, p. 371-378

Rivera-Sylva,H.E.,Carpenter,K.,Aranda-Manteca,F.J.,2011,LateCretaceousnodosaurids(Ankylosauria:Ornithischia)fromMexico:RevistaMexicanadeCienciasGeológicas,v.28,núm.3,p.371-378.

Rivera-Sylva et al.372

INTRODUCTION

Nodosauridankylosaursformanimportantcompo-nentoftheLateCretaceousdinosaurfaunainthenorthernhemisphere,especiallyEurope, theUnitedStates,andCanada(Coombs,1978;Carpenter,2001).Recently,how-ever,nodosauridshavebeenreportedfromthesouthernhemisphere,includingArgentina(CoriaandSalgado,2001)andAntarctica(Gaspariniet al.,1987;1996).CrucialtounderstandingthedistributionoftheseankylosaursarespecimensfromMexico.

In 1971, Harley J. Garbani found the first evidence ofanankylosaurfromBajaCalifornia,anosteodermfromElGalloFormation(Campanian).ThespecimenwasonlymentionedbyMorris(1967)andtheosteodermwasheldintheLosAngelesCountyMuseum.LateritwastransferredtotheColecciónNacionaldePaleontologíaintheUniversidadNacionalAutónomadeMéxico(UNAM).Unfortunately,thespecimencannotbelocated(Perrilliat,pers.com.,2009),thusitsidentityasnodosauridorankylosauridremainsun-known.AnewspecimenofankylosaurfromBajaisatoothfromtheElJabóncreeklocality,ElDisecadomember,ElGalloFormation(Campanian),BajaCalifornia,Mexico.In2006,Rivera-SylvaandEspinosa-Chávezreportedthepres-enceofankylosaurosteodermsfromtheCerrodelPuebloFormationinCoahuila,Mexico.Sincethen,additionalun-describedankylosaurremainshavebeenfoundintheUpperCretaceousofMexico(Meyeret al.,2005),includingtwovertebraeandametatarsalfromtheSanCarlosFormation

inAldama,Chihuahua(Figure1).WedescribesomeofthisnewmaterialhereandhighlightdifferenceswithspecimensfromcontemporaneousformationsofthenorthernUnitedStatesandsouthernCanada.Thesedifferencessuggestthatthemexicannodosauridsrepresentatleastonenewtaxon,butatpresentwerefrainfromnamingitowingtothefrag-mentarynatureofthematerial.

Theabbreviationsusedinthisstudyareasfollows:AMNH=AmericanMuseumofNaturalHistory,NewYork,NewYork,USA;CPC=ColecciónPaleontológicadeCoahuila,MuseodelDesierto,Saltillo,Coahuila,Mexico;UABCFCM=UniversidadAutónomadeBajaCaliforniaFacultaddeCienciasMarinas,Ensenada,BajaCalifornia,Mexico.

SYSTEMATIC PALAEONTOLOGY

SuborderThyreophoraNopcsa,1915InfraorderAnkylosauriaOsborn,1923

FamilyNodosauridaeMarsh,1890Nodosauridaeindet.

Specimen A

Materialexamined.UABCFCM2625,onetoothcrown(Figure2).Occurrence. ThematerialwasrecoveredingreymudstonefromElDisecadoMemberof theElGalloFormation(Campanian),ElJabónravine,BajaCalifornia,Mexico

Figure1.MapofMexicoshowingknownlocalitieswithnodosauridmaterial,1)ElRosario,ElGalloFormation,B.C.;2)Aldama,SanCarlosFormation,Chihuahua;3)LaSalada,AgujaFormation,Coahuila;4)SanMiguel,PenFormation,Coahuila;5)ElPelillal,CerrodelPuebloFormation,Coahuila.


cross-section.Thedistalcondylesarewellpreserved,andbothareaboutequalinsize,althoughthemedialcondyleextendsventrallybeyondthelateralcondyle.Incontrast,inbothEdmontoniaandPanoplosaurus themedialcondyleissmallerthanthelateralcondyleanddoesnotextendventrallyverymuchbeyondthelateralcondyle.

Theleftulnalacksthedistalthird(Figure3i-3l).TheolecranonismostsimilartothatofStegopelta(CarpenterandKirkland,1998)inthatitisaprominent,nearlyparallel-sidedforminlateralviewandistruncatedproximally;thisisincontrasttothemoreusualtaperingorconicalprocessinmanyankylosaurs(Carpenter,pers.obs).Inanteriorview,theolecranonresemblesthatofmostankylosaurs,beingabroad,invertedrighttriangle.However,theproximalendisrounded,ratherthantaperedasinSauropelta. Thehumeralnotchatthebaseoftheolecranoniswelldeveloped,whereasthelaterallyplacedradialnotchisshallowasistypicalofankylosaurs(Carpenter,pers.obs).

Theleftfemurisrepresentedbythedistalthird.Theintercondylargrooveisshallow.Thedistalendisslightlywiderthantheshaft(Figure3),whereasinEdmontonia,the distal end flares significantly wider than the shaft (the femurisunknowninPanoplosaurus).Posteriorly,thelateralcondylar ridge (sometimes referred to as the fibular process), issquareandprominent.

Along,tapered,slightlycurved“horn”-likestructureisprobablyadistalthoracicosteodermthatismissingitsbase(Figure3m-3p).Incross-section,theosteodermisel-liptical,beingdeeperthanwide.Oneside(anterior?)hasvasculargroovesextendingthelengthofthebone,thussomewhatresemblingaceratopsianhorn-core.

Specimen C

Material examined.CPC273consistsoftwocaudalverte-bra(CPC273/1;CPC273/2),onecervicalrib(CPC273/3),sixribfragments(CPC273/4),aposteriorfragmentofilium(CPC273/5),proximalfragmentof?tibia(CPC273/6),proximalendof?femur(CPC273/7);thirteenosteoderms

(N30º03’14”;W115º45’44”)(Figure1).Description.Thespecimenconsistsofa toothcrownlackingtheroot.Itmostcloselyresemblesthoseofothernodosauridsinitsrelativelylargesize,presenceofacom-pleteshelf-likecingulum,andlowdenticlecountalongthemargins(6anteriorlyand3posteriorly).Thecingulumisirregularonthelabialside,whereasonthelingualsideitissmoothandconcave.

Teetharetaxonomicallyusefulatthefamilylevelinankylosaurs(CoombsandMaryanska,1990).Toothcrownsofnodosauridsareproportionallylarge,withfewdenticles(4-8)alongthemarginsthatinmostcasesextendontothecrownfaceasridges(Coombs,1990).Thebaseofthecrownisswollenandacompletecingulumispresentononeorbothsides.Incontrast,theteethofpolacanthidsandanky-losauridsaresmall(Carpenter,pers.obs.,2001).

Specimen B

Material examined.CPC272,onedorsalvertebra,onecaudalvertebra,distalendofhumerus,partialulna,distalendoffemur,oneribfragment,andoneosteodermalspine(Figure3).Occurrence. ThematerialwasrecoveredfromtheshaleofthemarinememberofthePenFormation(Campanian),southofSanMiguel,Coahuila,Mexico(N28º38’16”;W102º56’55”)(Figure1).Description.Thedorsalvertebraconsistsprimarilyofthecentrum(Figure3e-3h).Ithasatypicalankylosaurianmor-phology,beingamphiplatyan,spool-shapedandconstrictedinthemiddle;itislongerandtallerthanwide.Aportionofonepeduncleispresent,butotherwisetheneuralarchandspinearemissing.Thecaudalvertebraconsistsonlyofadamagedcentrum,withtheneuralarchandspinemissing.Thecentrumisanteroposteriorlyshorterthanwide,andsomewhathexagonalinproximalview,asinmanynodo-saurids(Carpenter,pers.obs.).

Thelefthumerusconsistsofthedistalend(Figure3a-3d).Theincompleteshaftismediolaterallyellipticalin

Figure2.UABCFCM2625,nodosauridtoothfromBajaCalifornia,Mexico,in(a)labial,(b)lingual,(c)cranial,and(d)distalviews.Theocclusalsurfaceisup.Scalebar=5mm.

a) b) c) d)


Figure3.CPC272,nodosauridelementsfromCoahuila,Mexico.Distalendofrighthumerusin(a)dorsal,(b)ventral,(c)anterior,and(d)posteriorviews;dorsalvertebrain(e)cranial,(f)caudal,and(g-h)lateralviews;rightulnain(i)dorsal,(j)ventral,and(k-l)lateralviews;osteodermalspine(m-p).Scalebar=5cm.

a) b)

c)

d)

e) f)

g) h)

i) j)

m)

n)

o)

p)

k) l)


Figure 4. CPC 273, nodosaurid elements from Coahuila, Mexico, in superficial view. Dorsal osteoderms CPC 273/13-15 (a-c); fragment of ?thoracic osteodermCPC273/18(d);ossicleCPC273/19(e);distalosteodermCPC273/16(f);medialcervicalosteodermsCPC273/8-9(g,h);osteodermalspine(i).Scalebar=5cm.

(CPC273/9;CPC273/10;CPC273/11;CPC273/12;CPC273/13;CPC273/14;CPC273/15;CPC273/16;CPC273/17;CPC273/18;CPC273/19;CPC273/20;CPC273/21;CPC273/22),proximalendofscapula(CPC273/23),andtwentysevenundeterminedbonefragments(CPC273/24)(Figure4,Table1).Occurrence. ThematerialwasrecoveredinsandymudstonelayersfromthetheupperunnamedmemberoftheAgujaFormation(Campanian),westoftheElCarricito,townshipofOcampo,Coahuila,Mexico(N28º55’17”;W103º19’72”)(Figure1).Description.Thevertebraeandthetibiawerecollectedfromthesamesiteastheosteodermsandthesearethereforeassumedtobelongtothesameindividual.

Vertebrae.CPC273/1isacaudalvertebra,bearingfacetsforribarticulation.Theneuralcanaliscircularandbrokendorsally.Theneuralspineisbroken.Theventralsurfaceisweathered.Incontrast,CPC273/2hasashorttransverseprocess.Mostofthesurfaceofthecentrumiseroded;thereisaforamenonitsventralsurface.

Tibia.Apartialrighttibiaisrepresentedbytheproxi-malend.Ithasashortcnemialcrestlocatednearthemedialedge.Thelateralsideismissing,thustherelativewidthversuslengthofthetibialplateaucannotbedetermined.

Ilium.Aroundedfragmentmaybethepostacetabularprocessoftherightilium.Thedorsalsurfaceisslightly

concave,whereastheventralsidehasaroundedreinforcingridgeorbuttressthatextendsthelengthofthefragment.ItsdistalterminationisbluntandmayhavebeentheoriginoftheM.caudofemoralis brevis.Thisridgeisoffsettowardsthemedialhalf.Thepreservedportionistooincompleteforcomparisonwithotherilia.

Scapula.Thescapulaisrepresentedbythescapularmarginoftheglenoidcavity.Theangleoftheglenoidsug-gestsitisaleftscapula.Unfortunately,itdoesnotpreservethedorsalmarginoracromionprocess.

Osteoderms.CPC273/9(Figure4g)is largeandrectangular,withamediankeelthatistallerposteriorlyandterminatesinaconicalpointneartheosteoderm’sposteriormargin;itslateralmarginisbroken.CPC273/10andCPC273/11havethesameanatomicalfeaturesasCPC273/9butbotharebrokenintheirmiddles.CPC273/12isaconicalanterolaterally-directedcervicalspine(Figure4i).CPC273/13,CPC273/14,andCPC273/15arecircularwithalowkeelandareofthetypefoundinthethoracicregionofEdmontonia(Carpenter,1990)(Figure4a-4c).CPC273/16isadistalthoracicosteoderm.CPC273/17isacaudalosteoderm.CPC273/19isacircularossicle(Figure4e).The superficial surface is flat; the deep surface is flat to slightly concave. The superficial surface is pitted, grooved, andrugose.Themarginisrounded.

CPC273canbeattributedtotheNodosauridaebased

a) b)c)

d) e)

f) g)

h)i)


ontheanterolaterally-directeddistalcervicalspineandthekeeledthoracicosteodermsthatareslightlyexcavatedontheirdeepsurface(Vickaryouset al.,2004; Lee,1996;Sereno, 1986). The superficial surface texture of the osteo-dermsmostcloselymatchesthatreportedbyBurns(2008)forGlyptodontopeltainthatthesurfaceisgenerallysmooth,butthereareafewrandomlydistributedsmallpitsandvasculargroovesthatradiatefromthekeel.Thesediffer,however,inthatthepittingislessextensive.

Specimen D

Material examined.CPC275,caudalvertebra.Occurrence. Thematerialwasrecoveredfromsandstonelay-ersfromtheCerrodelPuebloFormation(Campanian),northofSaltillo,Coahuila,Mexico(N26º10’48”;W101º16’48”).(Figure1).Description.CPC275isacaudalvertebraerodedonmostofitssurface.Itconsistsofacentrumlackingmostoftheneuralarchandspine,andthetransverseprocess.Thecentrumisshortanteroposteriorlyandhasapairofchevronfacetsontheposteroventraledge.Inposteriorview,thecentrumhasthecharacteristichexagonalshapeofanodosaurid.

DISCUSSION

Thetooth(UABCFCM2625)issimilartothatofAletopelta coombsi(FordandKirkland,2001)fromtheUpperCretaceousofsouthernCalifornia.FordandKirkland(2001)considerAletopelta tobeanankylosauridandnotanodosauridasoriginallydescribedbyCoombsandDemere(1996).However,Aletopeltaalsohasnodosauridcharactersincludingtoothmorphologyandosteodermsthatarethickerthanthoseoftypicalankylosaurids(Carpenter,pers.obs.).

ThespecimenCPC273isanodosauridbecausetheosteodermsarethickandhaveaslightlyconcavebase.CPC272 is also identified as a nodosaurid primarily because of theelongateosteodermalspine.

Although four nodosaurids have thus far beenidentified from the Upper Cretaceous of North America (Panoplosaurus,Edmontonia,Glyptodontopelta,andAletopelta),specimenBfromthePenFormationsuggeststhe presence of a fifth genus (Table 2). However, the mate-rialistoofragmentarytobenamed.

OsteodermsrepresentthemostabundantmaterialamongtheMexicanspecimens.CPC273/12issimilartothedistal osteoderm of the first cervical ring (Sternberg, 1928), somewhatlikethatprojectinganterolaterallyfromthecervi-calhalfringsofAMNH5665(Edmontonia;Matthew,1922;Carpenter,1990).Theoval,lowkeeledosteodermissimilartothelateralcervicalosteodermsillustratedforEdmontonia(Carpenter,1997),CPC273,andAMNH5665.However,thesurfacetextureisdifferentfromEdmontonia(Table2)inthatithaspittingandadentriticpatternradiatingfromthekeel(Burns,2008).

Lehman(1997)estimatedthatankylosaurscom-prisedonly8%ofthedinosaurfaunainthenearbyAgujaFormationintheBigBendregionofTexas.BasedonNorthAmericanlocalitiesofankylosaurtracksites(McCreaet al.,2001)andthepresenceofaquaticvertebratesassociatedwithankylosaurbonesandteeth,ankylosaursprobablypreferredhumidenvironments(Vickaryouset al.,2004).

However,manyAsianankylosaurslivedinaridorsemi-aridenvironments(Carpenter,1997)andtheirrarityin the Aguja Formation and other coastal and floodplain set-tings,suchastheCerrodelPuebloFormation,mayindicatethattheyweremorecommonininlandareasthatarenotwelldocumentedintheNorthAmericanfossilrecord.

CONCLUSIONS

ThediscoveryofnodosauridremainsintheUpperCretaceousofMexicoisnotunexpected.ThesearethesouthernmostoccurrencesofthefamilyinNorthAmerica.Twogeneraofnodosauridankylosaurshavebeenre-portedfromtheCampanianAgujaFormationofTexas,Panoplosaurussp.andEdmontoniasp.(Lehman,1987;Carpenter,1990;Weishampelet al.,2004;Vickaryouset

Specimen number

Bone Maximum length

Maximum height

Maximum width

CPC273/1 Vertebra 45 59 69

CPC273/2 Vertebra 57 61 80

CPC273/3 Cervicalrib 34 14 23

CPC273/5 Ilium 93 57 101

CPC273/23 Scapula 172 83 124

CPC273/6 ?Tibia 98 88 55

CPC273/7 ?Femur 107 66 92

CPC273/8 Osteoderm 76 35 93














Table1.Measurements(inmillimeters)ofCPC273.


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Coombs, W.P., Jr., Maryańska, T. 1990, Ankylosauria, inWeishampel,D.B.,Dodson,P.,Osmólska,H.(eds.),TheDinosauria:Berkeley,UniversityofCaliforniaPress,1stEdition,456-483.

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Ford,T.,Kirkland, J.I.,2001,Carlsbadankylosaur (Ornithischia,Ankylosauria):Anankylosauridandnotanodosaurid, inCarpenter,K.(ed.),TheArmoredDinosaurs:Bloomington,IndianaUniversityPress,239-260.

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Gasparini,Z.,PeresaSuberbiola,X.,Molnar,R.E.,1996,NewdataontheankylosauriandinosaurfromtheLateCretaceousoftheAntarticapeninsula,inNovas,F.E.,Molnar,R.E.(eds.),ProceedingsoftheGondwananDinosaurSymposium,MemoirsoftheQueenslandMuseum,39,583-594.

Lee,Y.,M.,1996,Anewnodosauridankylosaur(Dinosauria:Ornitischia)fromthePawPawFormation(LateAlbian)ofTexas:JournalofVertebratePaleontology,16,232-245.

Lehman,T.M.,1987,LateMaastrichtianpaleoenvironmentsanddinosaurbiogeography in theWestern Interior of NorthAmerica:Palaeogeography, Palaeoclimatology, Palaeoecology, 60,189-217.

Lehman,T.M.,1997,LateCampaniandinosaurbiogeographyintheWesternInteriorofNorthAmerica,inWolberg,D.A.,Stump,E.(eds.),DinofestInternational,Proceedings:AcademyofNaturalSciences,Philadephia,223-240.

Marsh,O.C.,1890,AdditionalcharactersoftheCeratopsidae,withnoticeofnewCretaceousdinosaurs:AmericanJournalofScience,ser.3,39,81-86.

Matthew,W.,1922,Asuper-dreadnaughtoftheanimalworld.ThearmoureddinosaurPalaeoscincus:NaturalHistory,22,333-342.

McCrea,R.T.,Lockley,M.G.,Meyer,C.A.,2001,Globaldistributionofpurportedankylosaurtrackoccurrences,inCarpenter,K.(ed.),TheArmoredDinosaurs:Bloomington,IndianaUniversityPress,413-454.

Meyer,C.,Frey,E.D.,Thüring,B.,Etter,W.,Stinnesbeck,W.,2005,DinosaurtracksfromtheLateCretaceousSabinasBasin(Mexico):Kaupia,14,41-45.

Morris,W.J.,1967,BajaCalifornia:LateCretaceousdinosaurs:Science,155(3769),1539-1541.

Nopcsa,F.,1915,DieDinosaurierdersiebenbürgischenLandesteileUngarns:MitteilungenJahrbuchderKöniglichenungarischengeologischenReichsanstalt,23,1-26.

Osborn,H.F.,1923,TwoLowerCretaceousdinosaursofMongolia:

al.,2004;Sankey,2010).TheremainsfromMexicomayrepresentone,both,oranewgenus.CPC275alsorepre-sents the first record of a nodosaurid from the Cerro del PuebloFormation.

ACKNOWLEDGEMENTS

Wearegratefultothefollowingindividualsfortheircontributiontothisproject:JoséManuelPadilla,AbrahamIsaíOyervidezSalazar,andJoséLópez,fromtheMuseodelDesierto.IleanadelaPeñaOviedo,JorgeA.OrtízMendieta,RubénGuzmánGutiérrez(SMA),ElizabethJardón,TatianaSánchezRodríguez(MHN),andHomeroHernández helped during field seasons. The Museo del Desiertoisalsothankedforsupportingthisinvestigation,andthereforeweappreciateArturoH.GonzálezGonzálezforhissupportofthisproject.WeareobligedtothankDanielPosadaMartínez(MUDE)forthedonationofSpecimenD.Inthesamemannerwewishtoextendouracknowledge-mentstotheauthoritiesofOcampoandthepeopleofSanMiguelfortheirkindassistanceandsupportforthisproject.WeareindebtedtoFranciscoPalomino,RafaelRodríguezandEdgarGuzmán(nowretired)fromINEGIandtotheinstitutionsandindividualsinvolvedinmanywaystothesuccessofthisproject.

REFERENCES

Burns,M.E.,2008,Taxonomicutilityofankylosaur (Dinosauria,Ornithischia)osteoderms:JournalofVertebratePaleontology,28(4),1102-1109.

Carpenter,K.1990,Ankylosaursystematics:ExampleusingPanoplosaurus andEdmontonia,inCarpenter,K.,Currie,P.J.(eds.),DinosaurSystematics:Approaches and Persepectives: Cambridge,CambridgeUniversityPress,281-298.

Carpenter,K.,1997,Ankylosaurs,inFarlow,J.,Brett-Surman,M.,(eds.),TheCompleteDinosaur:Bloomington,IndianaUniversityPress,308-316.

Carpenter,K.,2001,Phylogeneticanalysisof theAnkylosauria, inCarpenter,K.(ed.), TheArmoredDinosaurs:Bloomington,IndianaUniversityPress,454-483.

Carpenter,K.,Kirkland,J.I.,1998,ReviewofLowerandMiddleCretaceousankylosaursfromNorthAmerica,inLucas,S.G.,Kirkland,J.I.,andEstep,J.W.,(eds.),LowerandMiddleCretaceousTerrestrialEcosystems:NewMexicoMuseumofNaturalHistoryandSciencieBulletin,14,249-270.

Coombs,W.,1978,Thefamiliesoftheornithischiandinosaurorder

Taxon Thoracic osteoderm shape Superficial surface texture Keel

Panoplosaurus Elliptical,longerthanwide Highlypitted,producingslighttomoderatelyrugosetexture.

Edmontonia Elliptical,widerthanlong SmootherthanPanoplosaurus.Dendriticvasculargrooves.

Prominent,morelaterally-directed,originatesfromthemedialmarginextendsposteriorlytowardsthelateralmargin.

CPC273 Elliptical,widerthanlong Smoothsurfacetexture.Dendriticvasculargrooves.

Table2.Comparisonofnodosauridarmor.


AmericanMuseumNovitates,95,1-10.Rivera-Sylva,H.E.,Espinosa-Chávez,B.,2006,Ankylosaurid(Dinosauria:

Thyreophora)osteodermsfromtheUpperCretaceousCerrodelPuebloofCoahuila,Mexico:CarnetsdeGéologie,Brest,Letter2006/02(CG2006_L02),5.

Sankey, J., 2010, Faunal composition and significance of high-diversity, mixedbonebedscontainingAgujaceratops mariscalensisandotherdinosaurs,AgujaFormation(UpperCretaceous),BigBend,Texas,inRyan,M.J.,Chinnery-Allgeier,B.J.,Eberth,D.A.(eds.),NewPerspectivesonHornedDinosaurs:TheRoyalTyrrellMuseumCeratopsianSymposium:Bloomington,IndianaUniversityPress,520-537.

Sereno,P., 1986,Phylogenyof thebird-hippeddinosaurs (OrderOrnithischia):NationalGeographicResearch,2,234-25.

Sternberg,C.M.,1928,AnewarmoreddinosaurfromtheEdmontonFormationofAlberta:TransactionsoftheRoyalSocietyofCanada,22(sec.IV),93-104.

Vickaryous, M.K., Maryańska, T., Weishampel, D.B. 2004, Ankylosauria, inWeishampel,D.B.,Dodson,P.,Osmólska,H.(eds.),TheDinosauria,2ndEdition:Berkeley,UniversityofCaliforniaPress,363-392.

Weishampel,D.B.,Barrett,P.M.,Coria,R.A.,LeLoeuff,J.,Xing,X.,Xijin,Z.,Sahni,A.,Gomani,E.M.P.,Noto,C.R.,2004, Dinosaurdistribution,inWeishampel,D.B.,Dodson,P.,Osmólska,H.,(eds.),TheDinosauria2ndEdition:Berkeley,UniversityofCaliforniaPress,517-606.

Manuscriptreceived:February15,2011Correctedmanuscriptreceived:April15,2011Manuscriptaccepted:May9,2011

late cretaceous nodosaurids (ankylosauria: ornithischia - scielo

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