A new ankylosaur (Dinosauria: Ankylosauria) from the Lower Cretaceous Cloverly Formation of central...

A new ankylosaur (Dinosauria: Ankylosauria) fromthe Lower Cretaceous Cloverly Formation ofcentral Montana

William L. Parsons and Kristen M. Parsons

Abstract: A cranium and other associated skeletal elements representing a new ankylosaurid dinosaur, Tatankacephaluscooneyorum gen. et sp. nov. possess several diagnostic features that indicate that this new taxon differs from the onlyother known ankylosaur from the Cloverly Formation, Sauropelta edwardsorum. These features include a frontoparietaldome, an enlarged nuchal ridge that obscures the occipital region, a circular orbit, ventral curvature in the posterolaterallydirected paroccipital processes, a posteroventrally directed foramen magnum, and a number of features on the braincase.The phylogenetic analysis positions Tatankacephalus with Ankylosauridae based on its sharing of several characters withother members of this clade, including an enlarged nuchal segment that obscures the occiput in dorsal view, a ventrallycurving lateral profile of the cranium anterior to the orbit, pyramidal postorbital boss, laterally projecting pyramidal quad-ratojugal boss, the presence of a postocular shelf, the presence of paranasal sinuses, and the lack of a cingulum on a max-illary (or dentary) tooth. It is considered a basal member of Ankylosauridae because it retains premaxillary teeth and avisible lateral temporal fenestra, in contrast to the absence of premaxillary teeth and an obscured lateral temporal fenestrain younger members of this clade.

Resume : Un crane et d’autres elements squelettiques associes representant un nouveau dinosaure ankylosauride,Tatankacephalus cooneyorum, gen. et sp. nov., presentent plusieurs caracteres diagnostiques indiquant que ce nouveau taxonest different du seul autre ankylosaure connu de la Formation de Cloverly, Sauropelta edwardsorum. Parmi ces caracteres fig-urent un dome frontoparietal, une crete nucale agrandie qui cache la region occipitale, une orbite circulaire, la courbure ven-trale dans les processus paroccipitaux d’orientation postero-laterale, un trou occipital d’orientation postero-ventrale et diverselements de la cavite cerebrale. L’analyse phylogenetique place Tatankacephalus au sein des Ankylosaurides a la lumiere deplusieurs caracteres communs avec d’autres membres de ce clade, dont un imposant segment nucal qui masque l’occiput envue dorsale, un profil lateral a courbure ventrale du crane anterieurement a l’orbite, une bosse postorbitale pyramidale, unebosse quadratojugale pyramidale projetee lateralement, la presence d’un repli post-oculaire, la presence de sinus paranasauxet l’absence de cingulum sur une dent maxillaire (ou dentaire). T. cooneyorum est considere comme etant un membre inferi-eur des Ankylosaurides parce qu’il conserve des dents premaxillaires et une fenetre temporale laterale visible, alors que lesmembres plus recents de ce clade n’ont pas de dents premaxillaires et leur fenetre temporale laterale est masquee.

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IntroductionSince 1996, we have conducted a paleontological survey

of an area known as the Middle Dome region (Museum ofthe Rockies (MOR) reference No. CL-016), in WheatlandCounty, Montana. The exposed sediments of the MiddleDome region are primarily composed of the Lower Creta-ceous Cloverly Formation. Over the course of this project,we have recovered various amniote remains, including an in-determinate testudinid, crocodyliforms (two unidentified taxarepresented by a partial cranium and a separate mandible),four individual specimens of the small theropod Deinony-

chus antirrhopus (Ostrom 1969), large theropod teeth similarto those of Acrocanthosaurus atokensis (Harris 1998), threeindeterminate sauropod vertebrae and teeth resembling thoseassigned to sauropod Pleurocoelus nanus (Ostrom 1970), ju-venile and adult specimens of the ornithopod Tenontosaurustillettorum (Forster 1990), the nodosaurid Sauropeltaedwardsorum (Ostrom 1970), and an undescribed ankylosaurthat represents a new taxon. The description of this ankylo-saur taxon forms the basis for this contribution.

Prior to our survey of the Middle Dome region, all ankylo-saur skeletal elements recovered from the Cloverly Formationhave been attributed to the nodosaurid Sauropelta. This newtaxon is the second ankylosaur and the first member of theAnkylosauridae to be recovered from the Cloverly Formation.

Geological settingThe cranium of the new taxon was collected from within

the red mudstone layers in the basal portion of Unit VII (Os-trom 1970) of the Lower Cretaceous Cloverly Formation inHarlowton, Montana. The holotype locality is approximately1 km west of American Museum of Natural History(AMNH) locality 33-1, where Barnum Brown excavated Mi-

Received 2 April 2009. Accepted 31 August 2009. Published onthe NRC Research Press Web site at cjes.nrc.ca on 16 October2009.

Paper handled by Associate Editor H.-D. Sues.

W.L. Parsons1 and K.M. Parsons. Buffalo Museum of Science,Department of Geology, 1020 Humboldt Parkway, Buffalo, NewYork 14211 USA.

1Corresponding author (e-mail: [email protected]).

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Can. J. Earth Sci. 46: 721–738 (2009) doi:10.1139/E09-045 Published by NRC Research Press

crovenator celer (AMNH 3041; Makovicky and Sues 1998),which is located at SW 1/4 Section 26, Township 7N, Ran-ge16E, in Wheatland County, Montana (46815.592’N,109841.263’W). Units V, VI, and VII of the Cloverly Forma-tion are designated in relation to the stratigraphic position ofBrown’s Microvenator site (Ostrom 1970). These units canbe continuously followed from the AMNH 33-1 site to thepoint of excavation of the holotype of Tatankacephalus coo-neyorum and have been used to determine the stratigraphicposition of the new fossil material. The units within theseexposures conform to the Himes Member of the CloverlyFormation as described in studies of the Bighorn Basin re-gion of northern Wyoming (Kvale and Vondra 1993).

The Middle Dome region is defined by a roughly circularvalley, the perimeter of which is partially delineated by abroken series of cliffs exposing extensive outcrops of LowerCretaceous strata. Terrestrial and lacustrine environmentsare indicated by identifiable vertebrate and invertebrate fos-sils characteristic of these environments, as well as paleosolsediments possessing abundant caliche deposition and sand-stone channel deposits. This represents a terrestrial paleoen-vironment that was occasionally divided by the channels ofmeandering, low-energy, freshwater streams.

During the 1996 field season, we collected five large cra-nial fragments of an ankylosaur found in close association.Returning in 1997 and 1998, we recovered several smallercranial fragments, rib fragments, and two partial body osteo-derms. All of the skeletal elements were associated within3 m. This assemblage contained no duplication of any re-covered elements; all of the skeletal material is consistentin size suggesting that it represents a single individual.

Institutional abbreviationsAMNH, American Museum of Natural History, New

York, N.Y., USA; CEUM, College of Eastern Utah Prehis-toric Museum, Price, Utah, USA; DMNH, Denver Museumof Natural History, Denver, Colorado, USA; IVPP, Instituteof Vertebrate Paleontology and Paleoanthropology, Aca-demia Sinica, Beijing, China; KUVP, Kansas UniversityVertebrate Paleontology, Lawrence, Kansas, USA; MOR,Museum of the Rockies, Bozeman, Montana, USA; MWC,Museum of Western Colorado, Grand Junction, Colorado,USA; ROM, Royal Ontario Museum, Toronto, Ontario,Canada; SMU, Southern Methodist University, Dallas,Texas, USA; TMP, Royal Tyrrell Museum of Palaeontol-ogy, Drumheller, Alberta, Canada; USNM, National Mu-seum of Natural History, Washington, D.C., USA; andYPM, Peabody Museum of Natural History, Yale Univer-sity, New Haven, Connecticut, USA.

Systematic paleontology

Dinosauria Owen, 1842Ornithischia Seeley, 1887Thyreophora Nopcsa, 1915Ankylosauria Osborn, 1923Ankylosauridae Brown, 1908Tatankacephalus cooneyorum gen. et sp. nov.

HOLOTYPE: MOR 1073. Partial cranium consisting of a frag-mentary portion of the nasal region with a fragmentary in-

ternasal septum, premaxillary fragments with three alveoli,maxillary–nasal fragment, orbital–postorbital–quadratojugalfragment, an isolated (maxillary or dentary) tooth, and alarge posterior cranial fragment, including parietal, squa-mosal, occiput, dorsal portion of left quadrate, braincase,right postorbital, right orbit, partial pterygoids, basisphenoid,partial basioccipital, and parasphenoidal rostrum. Rib frag-ments and two ventrally concave, hollow, fragmentary os-teoderms may belong to the same individual.

ETYMOLOGY: Tatanka, Oglala language, refers to Bison bison;cephalus, Latin for head. In dorsal view, the cranium ofTatankacephalus is similar in proportions to the cranium ofBison bison. The specific name honors the family of JohnPatrick Cooney.

TYPE LOCALITY: Middle Dome region, Harlowton, WheatlandCounty, Montana, USA.

TYPE HORIZON: Cloverly Formation, Lower Cretaceous, lateAptian to early Albian (Ostrom 1970).

DIAGNOSIS: Medium-sized ankylosaurid with following auta-pomorphies: unsegmented, enlarged nuchal ridge; concavelateral process projecting from paroccipital process; andkeeled osteoderm on jugal process of quadratojugal dorsalto quadratojugal boss. Tatankacephalus differs from Gasto-nia (Kirkland 1998) in possession of premaxillary teeth; inregion of frontal and parietal, lateral profile of frontoparietaldome creates convex appearance of cranial roof; and nuchalshelf with dorsally obscured occiput. Tatankacephalus dif-fers from Gargoyleosaurus (Carpenter et al.1998; Kilbourneand Carpenter 2005) in lack of alignment of premaxillaryand maxillary tooth rows; in region of frontal and parietal,lateral profile of frontoparietal dome creates convex appear-ance of cranial roof; and circular orbit. Tatankacephalus dif-fers from Gobisaurus (Vickaryous et al. 2001,2004) inregion of frontal and parietal, lateral profile of frontoparietaldome creates convex appearance of cranial roof; visible lat-eral temporal fenestra; and width between squamosals lessthan width between supraorbitals. Tatankacephalus differsfrom Minmi (Molnar 2001; Vickaryous et al. 2004) in regionof frontal and parietal, lateral profile of frontoparietal domecreates convex appearance of cranial roof; visible lateraltemporal fenestra; and maximum premaxillary rostrumwidth greater than distance between posteriormost maxillaryteeth. Tatankacephalus differs from Shamosaurus (Tuma-nova 1987; Vickaryous et al. 2004) in presence of premaxil-lary teeth; in region of frontal and parietal, lateral profile offrontoparietal dome creates convex appearance of cranialroof; and visible lateral temporal fenestra. Tatankacephalusdiffers from Tsagantegia (Tumanova 1993; Vickaryous etal. 2004) in region of frontal and parietal, lateral profile offrontoparietal dome creates convex appearance of cranialroof; pyramidal quadratojugal boss; premaxillary teeth; ba-sipterygoid process fused with quadrate ramus of pterygoid;and basisphenoid length less than basioccipital. Tatankace-phalus differs from Cedarpelta (Carpenter et al. 2001) withlateral temporal fenestra visible in lateral view; in region offrontal and parietal lateral profile of frontoparietal dome cre-ates convex appearance of cranial roof; occipital condyleorientation directed posteroventrally; and quadrate–parocci-pital process fused. Tatankacephalus differs from Sauropelta

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(Vickaryous et al. 2004) in posteroventrally directed openingof foramen magnum; in region of frontal and parietal, lateralprofile of frontoparietal dome creates convex appearance ofcranial roof; nuchal shelf dorsally obscuring occiput; curvedlateral profile anterior to orbit; and circular orbit.

DescriptionThis description of the recovered skeletal elements of Ta-

tankacephalus cooneyorum will include some of the lesswell-known aspects of the cranial anatomy of ankylosaurs,as well as a comparison between the cranial characters ofTatankacephalus and Sauropelta. To this end, we have re-examined the cranial fragments of Sauropelta specimensAMNH 3035, YPM 5529, and YPM 5549 and comparedthem with the cranial material of Tatankacephalus. AlthoughSauropelta and Tatankacephalus share some similar cranialcharacters, several significant differences were revealed.Where it is pertinent, inclusion of these comparative data inthe description of the cranial elements of Tatankacephalushelps considerably to differentiate it from Sauropelta, aswell as other previously described ankylosaurs.

The cranium of Tatankacephalus (MOR 1073, holotype)was reconstructed from several associated fragments that allpertain to one individual. The right supraorbital, frontal, andposteriormost nasal portions of the cranium were consider-ably compressed below the plane of the original dorsal sur-face of the cranium. In Fig. 1A, the articulations of thesedorsal fragments are not certain; for this reason an ‘‘ex-ploded’’ view of the dorsal surface of the cranium (Fig. 1A)seemed most appropriate. Based on comparisons with Gar-goyleosaurus (Carpenter et al. 1998; Kilbourne and Carpen-ter 2005), we estimate the total reconstructed length of thecranium to be approximately 32 cm. Much of the lateral,ventral, and occipital elements could be prepared, reas-sembled, and described.

With so few cranial fragments of Sauropelta for compari-son, some questions as to the taphonomic integrity of thefragments have been raised by previous authors (Ostrom1970; Vickaryous et al. 2004). The three-dimensional bilat-eral symmetry of Sauropelta specimen AMNH 3035 indi-cates only a minimal degree of distortion. The same is truein the ventral and occipital cranial elements of Tatankace-phalus (MOR 1073).

Through both direct observation and analysis of the com-puterized tomography (CT) scan images, it has been deter-mined that the sutures between the skeletal elements thatform the braincase of the cranium of Tatankacephalus arefused. This indicates that this specimen was a skeletally ma-ture individual (Jacobs et al. 1994; Barrett et al. 1998).

In lateral view (Fig. 1B), starting from the posterodorsaledge, the outline of the dorsal profile of the cranium of Ta-tankacephalus defines the apex of the enlarged nuchal ridge,after which it defines a shallow depression between the nu-chal ridge and the posterior limit of the frontoparietal dome.The profile delineates the curvature of the frontoparietaldome. The dorsal surface of the mid-section of the nasalchamber is represented only by a small intact fragment, butthis fragment allows for an approximation of the dorsal limitof the profile immediately anterior to the orbital region. Theapex of the dorsal limit of the cranium is immediately ante-

rior to the orbital region. The anterior profile slopes ven-trally as it continues along the dorsal surface of the nasalchamber toward the premaxilla. At the premaxilla, the de-gree of curvature of the profile diminishes slightly. Thisventrally curving lateral profile of the cranium anterior tothe orbit is a character seen in members of Ankylosauridae,such as Gastonia (Kirkland 1998), Euoplocephalus (Vickar-yous and Russell 2003), and Ankylosaurus (Carpenter 2004).

In dorsal view (Fig. 1A), the maximum cranial width isapproximately 75% of the estimated cranial length. Amongthyreophorans, a cranium longer than wide is characteristicof many stegosaurs and nodosaurid ankylosaurs. Within An-kylosauria, nodosaurids typically have skulls that are longerthan wide (Vickaryous et al. 2004), but this feature ispresent as well in some ankylosaurids, such as Gastoniaand Shamosaurus (Tumanova 1987). The lateral expansion

Fig. 1. Tatankacephalus cooneyorum gen. et sp. nov. (MOR 1073,holotype). (A) Composite photographic image of ‘‘exploded’’ viewof dorsal surface of cranium. Composite image created from asso-ciated, but not articulated, fragments of cranial elements that makeup the dorsal surface. (B) Illustration of left lateral surface of apartially reconstructed cranium. Composite illustration created fromassociated fragments from both left and right sides of cranium. clp,concave lateral process on lateral surface of paroccipital process;ecle, emargination of posterior lateral edge of cranium; fpd, fronto-parietal dome; j, jugal; kjo, keeled jugal osteoderm; lf, lateral tem-poral fenestra; m, maxilla; map, maxillary alveolar process; n,nares; nr, nuchal ridge; o, orbit; oo, orbital osteoderm; pm, pre-maxilla; pob, postorbital boss; pp, paroccipital process; q, quad-rate; qjb, quadratojugal boss; sdo, small dermal ornamentation;sob, supraorbital boss; sq, squamosal.

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of the maxillary region appears to correlate with the pres-ence of the paranasal sinus cavities. The nasal region tapersanteriorly.

The plane of the occiput is at an angle of 908 to the hori-zontal plane of the dorsal surface of the cranium. When ver-tical, the position of the occiput along with the overallcurvature of the dorsal profile of the skull positions the pos-terior edge of the enlarged nuchal ridge slightly beyond thevertical plane of the occiput; thus it overhangs and obscuresthe occipital region. This character is frequently seen inmembers of Ankylosauridae. In dorsal view, the nuchal crestof the foramen magnum is the only portion of the occipitalregion projecting beyond the obstruction of the overhangingnuchal ridge (Fig. 2A). In contrast, in Fig. 2B—the dorsalview of the posteriormost portion of Sauropelta specimenAMNH 3035—the occiput is not obscured by the nuchalridge. The plane of the occipital region is anterodorsally in-clined, which in dorsal view exposes both the occipital re-gion and the occipital condyle.

Anterior regionThe anterior region of the cranium exhibits a considerable

degree of damage. As in all of the other regions of the cra-nium, many of the external delineations of the various cra-nial elements are either indistinct due to the completefusion of sutures or obscured by overlying osteoderms.Nevertheless, analysis of the ornamentation patterns is taxo-nomically informative.

premaxillaFragments of both premaxillae have been preserved. The

right premaxilla includes a portion of the tooth row, whichretains three empty alveoli. Anterior to the nares, this por-tion of the premaxilla, which is still attached to the narialregion, provides some evidence of lateral expansion(Fig. 3). The left premaxilla includes part of the premaxil-lary shelf contributing to the secondary bony palate. Orna-mentation is in the form of a few large, slightly raisedsegments on the dorsal and lateral surfaces (Fig. 1B). Thepremaxillary tomia continues posteriorly beyond the dentig-erous portion of the edge of the premaxilla. It is not contin-uous with the maxillary alveolar process; instead, itposterolaterally parallels the maxillary alveolar process.

The nares are medially offset from the anterolateral edgeof the premaxillary tooth row, although not as far mediallypositioned as the nares of Euoplocephalus. The fragmentsof the external nares that are present indicate that they werelaterally positioned.

Fig. 2. Comparison of dorsal views of occipital regions on Tatankacephalus cooneyorum gen. et sp. nov. (MOR 1073, holotype) and Saur-opelta edwardsorum (AMNH 3035). (A) Dorsal view of posteriormost cranial fragment of Tatankacephalus (MOR 1073). (B) Dorsal viewof occipital region of Sauropelta (AMNH 3035). Photographs of AMNH 3035 courtesy of American Museum of Natural History. fm, fora-men magnum; ncfm, nuchal crest of foramen magnum. For other abbreviations, see Fig. 1.

Fig. 3. Ventral view illustration of maxillary alveolar process, pre-maxillary tooth row, and fragmentary premaxilla of Tatankacepha-lus cooneyorum gen. et sp. nov. (MOR 1073, holotype). Cross-hatching indicates breakage. emtr, endentulous portion of maxillarytooth row; is, internasal septum; ma, maxillary alveoli; nc, nasalcavity; pa, premaxillary alveoli. (3.4 inches width � 4.43 inchesheight (1 inch = 2.54 cm), planned for column width); m, maxilla;map, maxillary alveolar process; pm, premaxilla.



MaxillaBoth maxillae were preserved (Fig. 3). The maxillary al-

veolar process and premaxillary tooth row are not continu-ous or aligned with each other (Fig. 3). The maxillaryalveolar process possesses very little curvature. An edentu-lous ridge continues anteriorly from the recessed mesiallimit of the maxillary alveolar process to a midpoint nearthe lateral edge of the premaxilla. This edentulous ridge pos-sesses a sinusoidal curvature and is considerably diminishedin thickness in comparison to the maxillary alveolar process.

The emargination of the maxillary alveolar process is lat-eral to the maxillary alveolar process; it is deep, although itsdepth becomes increasingly shallow as it continues towardthe orbit. This emargination continues onto the anterior por-tion of the jugal.

A fragment of the right maxilla contains a large maxillarysinus. Referencing to Witmer and Ridgely (2008), this max-illary sinus corresponds to their description of the anteriorloop of the paranasal sinuses. This sinus (Fig. 4) is oval incross-section with the long axis of the oval aligned with thevertical axis of the cranium, and it ‘‘inflates’’ the lateralmaxillary portion of the wall of the nasal chamber. This si-nus cavity continues for the entire length of the maxillaryalveolar process. A complete septum separates this maxillarysinus from the more medial nasal cavities.

Nasal and prefrontalThe nasal and prefrontal regions are identified based on

the presence of the internasal septum. Portions of these re-gions from both the left and right sides of the cranium werepreserved. Even though much of the roof of the nasal cham-ber was damaged (Figs. 1A, 1B), two shallow grooves de-marcate fragmentary portions of two large, slightly raised,flattened areas of ornamentation within the anterior nasal re-gion. The internasal septum makes complete contact withthe roof of the nasal chamber, which it completely divides.Within the sedimentary matrix that filled the nasal chambersand encased the fragmentary internasal septum, some iso-lated fragments of thin, flat bone were found.

LacrimalThe lacrimal is defined based on the margin of the orbital

cavity and the presence of the nasolacrimal canal. It waspoorly preserved, although it can be determined that itmade up the anterior margin of the orbit. Breakage withinthis region revealed that the lacrimal possessed a large naso-lacrimal canal (Fig. 5B).

Temporal regionAlthough the sutures between bones are completely fused

and obscured in the temporal region, there are distinct dif-ferences in the cranial dermal ornamentation on Tatankace-phalus and Sauropelta (Figs. 2, 6). Sauropelta specimenAMNH 3035 (Fig. 6B) possesses a considerable degree ofdermal ornamentation on the lateral surfaces of the cranium;it continues down from the squamosal and infills the con-cavity of the lateral temporal fenestra, thus obscuring thisfenestra. It continues onto portions of the quadrate and post-orbital and encircles the ventral portion of the base of thepostorbital boss. In contrast on Tatankacephalus (Fig. 6A),on the dorsal surface of the parietal and supraorbital regions

and the nuchal ridge, although there is a patterning ofgrooves that break up the surface into a ‘‘mosaic’’ ornamen-tation of smaller shapes, dermal ornamentation does not in-fill the lateral temporal fenestra or cover the lateral surfaceof the squamosal or at the base of the postorbital boss.

The circular orbit of Tatankacephalus (Figs. 1B, 7A) dif-fers from the oval orbit of the Sauropelta specimens AMNH3035 (Fig. 7B) and YPM 5549 (Fig. 7C), as well as from thedescription of the orbit in Sauropelta by Ostrom (1970).Given the few specimens available, there is a possibilitythat the oval outline of the orbit of Sauropelta is a tapho-nomic artifact, but with two examples of an oval outlinefrom specimens from two separate sites (Figs. 7B, 7C), theevidence argues in favor of the interpretation of the originalshape of the orbit as oval.

Although the orbital rim of Tatankacephalus is missing asmall segment in its ventral region, the structure of this rim

Fig. 4. Photograph and illustration of a cross-section of the rightposteriormost maxillary region of the cranium of Tatankacephaluscooneyorum gen. et sp. nov. (MOR 1073, holotype). Tonal stipplingwithin illustration represents preserved material. mmss, medialmaxillary sinus septum; ms, maxillary shelf; mxs, maxillary sinus;map, maxillary alveolar process; pm, premaxilla; nc, nasal cavity.



indicates that, in its original state, it was completely sur-rounded by flat orbital osteoderms. Small portions of the os-teoderms have natural separations from the underlying bone.These orbital osteoderms are similar to the structure de-scribed as a ‘‘dermal bony ring’’ in Tianzhenosaurus youngi(Pang and Cheng 1998, p. 326). The dorsal portions of theosteoderms that encircle the orbital rim differ from those inthe region of the orbital osteoderms of Sauropelta (AMNH3035, YPM 5549) (Figs. 7B, 7C). The dorsal portions of theosteoderms of Sauropelta terminate immediately below thesupraorbital boss and do not continue upward to encirclethe orbit along its dorsal edge as they do in Tatankacephalus(Fig. 7A).

Although the fragmentary nature of the cranium of Tatan-kacephalus makes some alignments speculative, the orienta-tion between the postorbital and quadratojugal bosses comes

from the reconstructions of two large, well-defined frag-ments that were clearly and solidly realigned in the onlypossible fitting. This presents the original undistorted orien-tation between the postorbital and quadratojugal bosses.With all the quadratojugal bosses of both Tatankacephalusand the two specimens of Sauropelta aligned at a similar an-gle (Fig. 7), the apex of the pyramid form of the postorbitalboss of Tatankacephalus (Fig. 7A) lies below the midpointof the orbit, which is in contrast to the position of the twosimilar end points on the postorbital bosses on both Sauro-pelta specimens (Figs. 7B, 7C). The ends of the postorbitalbosses on these two Sauropelta specimens align with dorsalrims of their respective orbits. The similarity in generalstructure of these Sauropelta cranial fragments (Figs. 7B,7C) is further evidence that the oval structure of these orbitsis not a product of taphonomic distortion.

Fig. 5. Photographs and schematic of neurovascular and nasolacrimal canals of Tatankacephalus cooneyorum gen. et sp. nov. (MOR 1073,holotype). (A) Photograph of internal surface of lingual maxillary region, within which is located neurovascular canal. (B) Photograph ofright postorbital boss, orbit, and cross-section of nasolacrimal canal revealed due to breakage. Schematic illustration of lateral view of com-posite cranium with median line indicating internal position of nasolacrimal canal and rectangular inset indicating position of maxillary–palatine fragment, which contains neurovascular canal. Cross-hatching indicates breakage. map, maxillary alveolar process; mmss, medialmaxillary sinus septum; nlc, nasolacrimal canal; nvc, neurovascular canal.



SupraorbitalDirectly above the dorsal orbital rim and immediately an-

terior to the postorbital boss, there is a single supraorbitalboss (Figs. 1B, 8). Its dorsal surface is aligned with the sur-face of the rest of the supraorbital region. In lateral view, itis rhomboidal. It projects laterally beyond the lateral planeof the postorbital boss. The ventral edge of the supraorbitalboss is separated from the rim of the orbit by the dorsal por-

tion of the orbital osteoderms. Any further dorsal surfacefeatures anterior to this enlarged segment cannot be ob-served because of damage.

The posterodorsal surface of the supraorbital region(Fig. 2A) bears an ornamentation pattern of smaller dermalplates and grooves. The ornamentation patterns on the rightand left supraorbital regions differ in the size of the individ-ual segments and the orientation of the groove patterns

Fig. 6. Comparison of views of right lateral temporal fenestra and surrounding cranial elements on Tatankacephalus cooneyorum gen. et sp.nov. (MOR 1073, holotype) and Sauropelta edwardsorum (AMNH 3035). (A) Right lateral temporal fenestra region of Tatankacephalus(MOR 1073). (B) Right lateral temporal fenestra region of Sauropelta (AMNH 3035). clp, concave lateral process on lateral surface ofparoccipital process; do, dermal ossification. For other abbreviations, see Fig. 1. Photograph of AMNH 3035 courtesy of American Museumof Natural History.

Fig. 7. Comparison of views of orbital regions of Tatankacephalus cooneyorum gen. et sp. nov. (MOR 1073, holotype) and Sauropeltaedwardsorum specimens (AMNH 3035, YPM 5549). (A) Left (horizontally flipped) orbital region of Tatankacephalus (MOR 1073). (B)Orbital region of Sauropelta (AMNH 3035). (C) Left (horizontally flipped) orbital region of Sauropelta (YPM 5549). qjb, quadratojugalboss. Photograph of AMNH 3035 courtesy of American Museum of Natural History. Photograph of YPM 5549 courtesy of Yale PeabodyMuseum of Natural History.



between the segments. The comparison of these two supra-orbital regions reveals an asymmetrical pattern across theposterodorsal surface of the cranium.

Figure 8 presents a comparison between the supraorbitalbosses on Tatankacephalus and Sauropelta. In contrast tothe supraorbital boss on Tatankacephalus, both lateral planesof the postorbital boss and the supraorbital boss on Sauro-pelta specimens AMNH 3035 and YPM 5549 (Figs. 7B, 7C)merge to create a continuous lateral surface. In dorsal view(Fig. 8C), these two bosses on Sauropelta specimen AMNH3035 combine and create a single, somewhat square, laterallyprojecting process. This differs from the laterally distinct andseparate supraorbital and postorbital bosses and the pyrami-dal postorbital boss found on Tatankacephalus (Fig. 8C).

PostorbitalThe postorbital forms the posterior portion of the orbital

rim. A postocular shelf medially projects from the postorbi-tal; its concave anterior surface forms a portion of the poste-rior border of the orbit. The postorbital bears ornamentationconsisting of a boss that includes the anteriormost portion ofthe squamosal. This boss is distinctly pointed, pyramidal,and laterally projecting (Figs. 1B, 7A, 8C). Its base is de-fined by circumferential grooves. In profile, the dorsal edge

of this boss is aligned with the curvature of the rest of thedorsal cranial surface, and it possesses distinct longitudinalridges that form a relatively sharp anterodorsal edge. Alsoin profile (Fig. 7A), the postorbital boss possesses two dis-tinct dorsal and ventral facets; this condition differs fromthe flat lateral surface of the postorbital boss in Sauropelta(Figs. 7B, 7C).

JugalThe ventral portions of the orbital rim and orbital cavity

are formed by the jugal (Fig. 7A). A shallow suborbital–ju-gal arch, present in Tatankacephalus has been described as acharacteristic of ankylosaurs (Sereno 1999). Below the orbi-tal rim, a small portion of the buccal emargination continuesonto the jugal. Although the sutures are obscured, it is appa-rent by the posterior extension of the maxillary alveolarprocess that the jugal articulates with the maxilla anteriorly.

Dorsally adjacent to the quadratojugal boss and within theregion of the posteriormost extension of the jugal and thejugal process of the quadratojugal, a smaller osteoderm(Fig. 7A) possesses a peaked keel-like structure, the edge ofwhich is dorsoventrally aligned with the laterally projectingdorsal edge of the quadratojugal boss. This is an autapomor-phy of this new taxon. An osteoderm of similar size ispresent in Pawpawsaurus campbelli (Lee 1996) and in onespecimen of Sauropelta (YPM 5499; Fig. 7C), although it isabsent in another Sauropelta specimen (AMNH 3035;Fig. 7B). In these two nodosaurids, the osteoderm is flat-tened and lacks the peaked keel-like structure found in Ta-tankacephalus. This may be a neomorphic character asdescribed by Vickaryous and Russell (2003), representingthe co-ossification of two smaller osteoderms.

Frontal–parietalThe exact sutural delineation of the frontals and the parie-

tals cannot be determined, but it is evident from the relation-ship between the position of this thickened region and theorbital region that at least a posterior portion of the frontals,as well as most of the anterior portion of the parietals, con-tribute to a modest but noticeable frontoparietal dome(Figs. 1A, 5, 9). This is similar to the domed structure inPanoplosaurus mirus (ROM 1215; personal observation).

Fig. 8. Comparison of supraorbital boss of Tatankacephalus coo-neyorum gen. et sp. nov. (MOR 1073, holotype) and Sauropeltaedwardsorum (AMNH 3035). (A) Dorsal view of right supraorbitalboss on Tatankacephalus (MOR 1073). (B) Lateral view of rightsupraorbital boss on Tatankacephalus (MOR 1073). (C) Dorsalview of right supraorbital boss on Sauropelta (AMNH 3035).Photographs of AMNH 3035 courtesy of American Museum ofNatural History. pob, postorbital boss; sob, supraorbital boss.

Fig. 9. Axial computerized tomography (CT) scan of cranium ofTatankacephalus cooneyorum gen. et sp. nov. (MOR 1073, holo-type). (A) Dorsal view of posteriormost cranial fragment. (B) CTscan cross-section revealing extent of development of parietaldome. CT scan by L.M. Witmer (Ohio University, Athens, Ohio)and H. Rockhold (O’Bleness Memorial Hospital, Athens, Ohio).fpd, frontoparietal dome; ncfm, nuchal crest of foramen magnum;pp, paroccipital process; sq, squamosal.



The thickening of the parietal region can be seen in the CTscan cross-section (Fig. 9). The surface of the frontoparietaldome is smooth, compared with the dorsal surface of therest of the cranium. The lateral and anterior limits of thethickened portion of the dome are not delineated by anywell-defined grooves or sutures. The posterior limit of thefrontoparietal dome tapers down and is defined by a shallowdepression that separates it from the posteriormost portion ofthe parietal region. The parietals form the roof of the brain-case.

The posteriormost portions of the parietals enlarge into acurved, domed nuchal ridge segment (Fig. 2A). This secon-dary doming is not as high or robust as the frontoparietaldome. Dorsal to the supraoccipital, this nuchal ridge formsthe medial portion of the posterodorsal edge of the cranium.Except for a transverse crest, which projects directly abovethe foramen magnum, this nuchal ridge projects posteriorlybeyond the plane of the occiput, and in dorsal view, itoverhangs and obscures the rest of the occipital region(Fig. 2A). The ornamentation in this region is not dividedinto large, distinct segments as in some ankylosaurids, suchas Euoplocephalus (Vickaryous and Russell 2003), Ankylo-saurus (Carpenter 2004), Saichania (Maryanska 1977), andTianzhenosaurus (Pang and Cheng 1998). Nevertheless, thisridge does possess an ornamentation pattern of small, flat-tened surfaces and finely patterned venation grooves. Theunique structure of this nuchal ridge makes this an autapo-morphy for Tatankacephalus. In Fig. 2A, the curved andposterodorsally enlarged structure of the nuchal ridge ofTatankacephalus is in contrast with the flat posterodorsalregion on Sauropelta specimen AMNH 3035 (Fig. 2B). Al-though a nuchal segment can be observed on the posterodor-sal surface of AMNH 3035, it is a flattened feature that alignswith the plane of the flat parietal surface of this specimen.

SquamosalThe squamosal is emarginated at the lateral temporal fen-

estra between the paroccipital process and the postorbitalboss. In dorsal view, it is enlarged to the point that its out-line (Figs. 1A, 2A) does not appear concave as in Panoplo-saurus (ROM 1215; Russell 1940; personal observation). Indorsal view, the outline of this squamosal region is straight,indicating a flat rather than concave lateral surface betweenthese two projecting processes. The relative distance be-tween the paroccipital process and the postorbital is notice-ably greater in Tatankacephalus (Fig. 2A) than inSauropelta (Fig. 2B).

QuadratojugalThe quadratojugal boss in Tatankacephalus is distinctly

pointed, pyramidal, and lateroventrally directed (Fig. 7A). Itdiffers from the single, flattened, ventrally directed quadra-tojugal bosses on Sauropelta specimen YPM 5499 andAMNH 3035 (Figs. 7B, 7C) in that the quadratojugal bossin Tatankacephalus is more laterally projected and moreventrally detached from the more medial quadratojugal sur-faces.

Palatal regionThe palatal region is particularly informative because of the

absence of the osteoderms that obscure most of the sutures on

the external surface of the cranium. Although this region isdamaged, several important characters are still present.

VomerA fragment of the ventral portion of the palatal contribu-

tion of the vomer is preserved (Fig. 10). A small remnant ofthe anteriormost portion of the vomer contacts the premaxil-lary palate. The dorsal extension of the vomer sagittally bi-sects the palatal region. The vomer contacts the premaxillaeat the medial, interpremaxillary sutural midpoint of the pos-terior margin of the premaxillae.

PalatineOn the oral surface of the posterior maxillary–palatine re-

gion (Fig. 5A), immediately posterodorsal to the mesial endof the maxillary alveolar process and close to the nasolacri-mal canal, there is a large neurovascular foramen. The fora-men for this canal is positioned along the palatine–maxillarycontact.

The premaxillary portion of the palatal shelf (Fig. 3) ispartially bifurcated at the midpoint of its posterior medialedge and is continuous with the anterolingual side of themaxillary alveolar process. This shelf contacts the maxillaryalveolar process at a point close to a remnant of one of theanterior maxillary tooth roots. Given the variable partial de-velopment of the secondary palate in other ankylosaurs, thisstructure is interpreted to be a modest development of theanterodorsal arch of the secondary palate (Vickaryous et al.2004).

PterygoidPortions of the pterygoids that lie anterior to the basisphe-

noid are damaged, but the remaining fragments possesssome important characters (Fig. 10). A fragment of the me-dial section of the quadrate ramus of the right pterygoid ispreserved. This fragment is fused to the short, right basipter-ygoid process. This fusion would have precluded the devel-opment of any movement between the pterygoid and thebasisphenoid, such as has been described by Kirkland(1998) in Gastonia. The posterior edges of the pterygoidsare incised by the anteriorly directed medial fissure of theinterpterygoid vacuity immediately posterior to the medialfusion of the pterygoids with the remnant of the vomer(Fig. 10). This anteriorly directed medial fissure of the inter-pterygoid vacuity lies between the pterygoids; thus, the pos-terior margin of the pterygoid of Tatankacephalus differsfrom the straight posterior edge of the transversely alignedpterygoid lamina in Pawpawsaurus (Lee 1996) and Pano-plosaurus (Russell 1940). It is more similar to the pterygoidstructure in Ankylosaurus (Carpenter 2004), Euoplocephalus(Coombs 1978), and Gobisaurus (Vickaryous et al. 2001).Although fragmentary, the beginning of the anterolateralmandibular ramus of the pterygoid projects outward fromthe anterior point of this medial fissure. The anterior face ofthe pterygoid body is primarily directed anteroventrally,though there is some vertical–ventral flexure of the posterioredge of the medial fissure of the pterygoids that is similar tothat of Ankylosaurus (Carpenter 2004) and also to the de-rived vertical condition described in Gobisaurus (Vickar-yous et al. 2001). The ectopterygoid regions are sodamaged or missing that no pertinent data can be obtained.



QuadrateWhat remains of the right quadrate is an anteroventrally

directed fragment projecting 3 cm below the dorsal apex ofthe lateral temporal fenestra. The quadrate is anteroventrallyflattened and the condyle is sheared off. From lateral andoccipital view, the quadrate is very broad. In lateral view,the quadrate is proportionally twice as broad as that on Sau-ropelta (AMNH 3035) (Figs. 6A, 6B). The anteroposteriorinclination is similar to that of Pawpawsaurus (Lee 1996).The quadrate and the paroccipital process are fused,although there is a remnant of the suture between these ele-ments.

The posterior edge of the lateral temporal fenestra is de-fined by the quadrate. In lateral view (Fig. 1B), the openingof the lateral temporal fenestra is partially obscured by thedevelopment of the postorbital and quadratojugal bosses.The preserved upper portion of the lateral temporal fenestraconforms to the shape of one end of a narrow oval, with asubvertical and slightly posteriorly inclined long axis. Themore medial portion of the lateral temporal fenestra narrowsbecause of the angle of the posteromedial extension of thequadrate ramus of the pterygoid.

As Ostrom (1970) pointed out, based on the complete an-terior margin on an isolated quadrate (YPM 5529), the lat-eral temporal fenestra on Sauropelta is open, but incomparison with Tatankacephalus (Figs. 6A, 6B), the dis-tance between the quadrate and postorbital on Sauropelta(AMNH 3035) is more constricted than the anteroposteriorwidth of the lateral temporal fenestra on Tatankacephalus.The exact nature of the structure of the lateral temporal fen-

estra on AMNH 3035 is obscured by the covering of thisfenestra by dermal ornamentation.

There is some separation between the dermal ornamenta-tion and the base of the postorbital boss on Sauropelta(AMNH 3035), which indicates that the possible fusion orat least adherence between these two forms of bone was notstrong. This fragmentary dermal ornamentation bone is in afragile condition. The dermal ornamentation appears to beexactly molded into the concavity of the lateral temporalfenestra. Clearly, there has been at least some taphonomicseparation and destruction of the dermal ornamentation inAMNH 3035, especially along the base of the postorbitalboss. If the dermal ornamentation can be relatively easilyseparated from the underlying bone, and it was originallyformed to conform to the concavity of the lateral temporalfenestra, then there is a possibility that any significanttaphonomic distortion would have dislodged the dermalossification from the concavity of the lateral temporalfenestra.

BraincaseMany elements of this region are completely fused. In

particular, the right lateral surface of the braincase, althoughwell preserved, does not exhibit any clear sutures betweenthe various constituent elements. Still, the braincase exhibitsseveral important features including the relatively straightalignment of the more posterior cranial nerve foramina (V,VII, IX, X, XI, and XII; Fig. 11), which, as confirmed bysagittal CT scanning (Fig. 12), indicates the oblique angledalthough straight attitude of the floor of the endocranial cav-

Fig. 10. Photograph and illustration of ventral view of large posterior fragment of cranium of Tatankacephalus cooneyorum gen. et sp. nov.(MOR 1073, holotype). Cross-hatching indicates breakage. bo, basioccipital; bpp, basipterygoid process; bs, basisphenoid; bt, basal tubera;ch, choana; fm, foramen magnum; ipv, interpterygoid vacuity; is, internasal septum; mf, medial fissure; mppf, mandibular process of pter-ygoid fragment; ocf, occipital condyle fragment; p, palatine; paf, proatlas facet; pos, postocular shelf; pp, paroccipital process; psr, para-sphenoidal rostrum; q, quadrate; qrp, quadrate ramus of pterygoid.



ity. The sagittal CT scan reveals that the braincase possessesan oblique orientation relative to the horizontal axis of thecranium. Following the anteroposterior axis, the structure ofthe braincase is approximately straight with only a small de-gree cerebral flexure that is noticeable along the dorsal sur-face. This degree of flexure is similar to that of the endocastof Cedarpelta (Carpenter et al. 2001).

SupraoccipitalAlthough its sutural contacts are fused and the nuchal

ridge partially obscures its demarcation, the supraoccipitalis sagittally positioned directly dorsal to the foramen mag-num. Dorsally, it contacts the enlarged, rounded nuchalridge. An inverted, Y-shaped crest is oriented vertically be-tween the nuchal ridge and the foramen magnum (Figs. 13,14A). This crest is similar to the one described in Euoploce-phalus (Vickaryous and Russell 2003), although the fossaethat are positioned on either side of this nuchal crest in Euo-plocephalus are indistinct concavities in Tatankacephalus.Immediately above the dorsal edge of the foramen magnum,a portion of the nuchal crest continues transversely to createa pair of flattened, oval tuberosities. This transverse portionof the nuchal crest differs from that in Euoplocephalus(Vickaryous and Russell 2003) in that the medial notch de-scribed in Euoplocephalus is absent in Tatankacephalus. Asdescribed by Vickaryous et al. (2004), the anteroposterior

Fig. 11. Photographs of braincases of Tatankacephalus cooneyorum gen. et sp. nov. (MOR 1073, holotype) and Sauropelta edwardsorum(YPM 5529). (A) Braincase of Tatankacephalus (MOR 1073) in left lateral view. (B) Braincase of Sauropelta (YPM 5529) in left lateralview. bpp, basipterygoid process; bt, basal tubera; cn I–XII, openings for cranial nerves I–XII; eo, exoccipital; fo, foramen ovalis; ic, in-ternal carotid foramen; ls, laterosphenoid; oc, occipital condyle; op, opisthotic; osc, otosphenoidal crest; pr, prootic. Photographs of YPM5529 courtesy of Yale Peabody Museum of Natural History.

Fig. 12. Sagittal computerized tomography (CT) scan of posteriorportion of cranium of Tatankacephalus cooneyorum gen. et sp. nov.(MOR 1073, holotype). CT scan by L.M. Witmer (Ohio University,Athens, Ohio) and H. Rockhold (O’Bleness Memorial Hospital,Athens, Ohio). bc, lateral image of braincase.



pitch of this transverse nuchal crest indicates a posteroven-trally facing foramen magnum.

Exoccipital–opisthoticDorsomedially, the exoccipital–opisthotic articulates with

the supraoccipital. The paroccipital processes are robust,posterolaterally directed, and considerably curved in a ven-trolateral direction (Fig. 14A). The ventrolateral curvatureof the paroccipital processes of Tatankacephalus is similarto that of the paroccipital processes on Euoplocephalus(TMP 91.127.1; Vickaryous and Russell 2003) and Gastonia(CEUM 1307; Kirkland 1998). On the lateral surface of theparoccipital process, there is a relatively thin concave, later-ally directed process. This process is an autapomorphy ofTatankacephalus. The foramen for the hypoglossal nerve

(XII) perforates the exoccipital–opisthotic and emerges ante-rior to the base of the occipital condyle (Fig. 11).

The ventral curvature of the paroccipital processes on Ta-tankacephalus differentiates this element from the straight,posterolaterally projecting paroccipital processes on Sauro-pelta (AMNH 3035) (Figs. 14A, 14B). The most lateralpoint of the paroccipital processes on Sauropelta (AMNH3035; Fig. 14B) is slightly above the midpoint of its fora-men magnum, whereas the comparable point of the parocci-pital processes on Tatankacephalus is well below themidpoint of its foramen magnum (Fig. 14A).

BasioccipitalConsiderable postmortem damage has affected the right

side of the braincase. The foramen magnum is slightly wider

Fig. 13. Photograph and illustration of cranium of Tatankacephalus cooneyorum gen. et sp. nov. (MOR 1073, holotype) in occipital view.Cross-hatching indicates breakage. cn XII, opening for cranial nerve XII; fm, foramen magnum; ncfm, nuchal crest of foramen magnum;ocf, occipital condyle fragment; paf, proatlas facet; ptfo, postemporal foramen. For other abbreviations, see Fig. 1.

Fig. 14. Comparison of occipital regions of Tatankacephalus cooneyorum gen. et sp. nov. (MOR 1073, holotype) and Sauropelta edward-sorum (AMNH 3035). Photographs taken at slightly oblique angles to compare vertical axes of two left proatlantal facets (paf). (A) Occi-pital region on Tatankacephalus (MOR 1073). (B) Occipital region on Sauropelta (AMNH 3035). oc, occipital condyle; fm, foramenmagnum; ncfm, nuchal crest of foramen magnum. For other abbreviations, see Fig. 1. Photograph of AMNH 3035 courtesy of AmericanMuseum of Natural History.



than it is high; its transverse diameter is 27.06 mm and itsvertical height is 26.11 mm (Fig. 14A). The proatlantal fac-ets form two posteriorly concave, curved surfaces on eitherside of the foramen magnum (Fig. 14A). The posteriorly in-clined angle of the long axes of these proatlantal facets isparallel to the rim of the opening of the foramen magnumand is oriented posteriorly at 248 below the horizontal planeof the dorsal cranial surface. This is a further indication thatthe foramen magnum opened posteroventrally and is consis-tent with the correlation between the inclination of the skulland the posteroventral pitch of the transverse nuchal crestabove the foramen magnum. This would indicate that thenormal orientation of the head of Tatankacephalus wouldhave been similar to the oblique orientation in Pawpawsau-rus (Lee 1996).

In Figs. 13A and 14A, the prominent nuchal crest directlyabove the foramen magnum on Tatankacephalus is in con-trast to the lack of this feature above the foramen magnumon Sauropelta (AMNH 3035) (Fig. 14B). There is some evi-dence of an incipient nuchal crest on the Sauropelta speci-men YPM 5529, but it is too fragmentary to determine anydetails of the structure. The foramen magnum of AMNH3035 is oval with a horizontal diameter of 31.86 mm and avertical diameter of 34.24 mm (Fig. 14B), which is in con-trast with the horizontally oval foramen magnum in Tatan-kacephalus. Also, the foramen magnum of AMNH 3035opens posteriorly, whereas that of Tatankacephalus opens ina posteroventral direction. This difference is confirmed bythe difference in the angle of the vertical axes of the proat-lantal facets on both of these taxa (Figs. 14A, 14B).

The dorsal margin of the basioccipital is partially definedby the ventral edge of the horizontally oriented, irregularlyshaped foramen (fenestra metotica), which contains theopenings for the glossopharyngeal (IX), vagus (X), and spi-nal accessory (XI) nerves (Fig. 11). Although the suture be-tween the basioccipital and the exoccipital–opisthotic isfused, the dorsoventrally flattened, anteroposteriorly elon-gate structure of this foramen gives some indication as tothe boundary between the dorsal margin of the basioccipital,which forms the ventral edge of this fissure, and the regionthat is considered transitional between the opisthotic andexoccipital, which forms the dorsal edge of this fissure.

ProoticThe foramen for the trigeminal nerve (V) indicates in part

the contact between the prootic and the laterosphenoid(Vickaryous and Russell 2003). The posterior edge of thisforamen creates a thin wall between this fossa and the ante-rior edge of the prootic ridge. The border of the prootic withthe laterosphenoid and basisphenoid forms a prominentridge. In a slightly posteroventral position in relation to thetrigeminal nerve (V) foramen, the facial nerve (VII) foramenpenetrates the wall of the prootic (Tumanova 1987). Poste-rior to the facial nerve foramen and positioned between theexoccipital–opisthotic and the prootic is the fenestra ovalis,into which would have been inserted the footplate of thecolumella (stapes).

BasisphenoidThe basisphenoid (Figs. 11, 15) is positioned between the

basioccipital and the parasphenoid. Its ventral surface has an

irregular, roughened rugose texture compared with the rela-tively smooth ventral surface of the anterior portion of thebasioccipital. The posterolateral position of the basal tuberaand the ventral cortical rugosity help to demarcate these twoelements and allow for the anteroposterior measurements ofboth of these two cranial elements. The anteroposteriorlength of the basisphenoid is 36 mm. Taking into considera-tion the loss of the occipital condyle, the anteroposteriorlength of the basioccipital is 42 mm. Thus, the basisphenoidis anteroposteriorly shorter than the basioccipital. The basip-terygoid processes project ventrolaterally from the basisphe-noid by less than 1 cm. The contact between the quadrateramus of the pterygoid and the basipterygoid process isfused. Posterior to the basipterygoid processes and directlyventral to the foramen ovalis, there are small, paired basaltubera. The basisphenoid contains a large foramen for theentrance of the internal carotid artery. Anteroventral to thecarotid foramen, some damage has occurred to the basisphe-noid region, but a portion of the otosphenoidal crest still re-mains intact.

Figures 11 and 15 present comparisons between the ven-tral surfaces of the basisphenoid and the available remnantsof the basipterygoid processes from both Tatankacephalusand Sauropelta. After taking into consideration the relativeproportions of other cranial elements within the region ofthe braincases of both taxa (in YPM 5529, the anteroposte-rior width of basipterygoid processes is 17.83 mm; whereas,it is 26.11 mm in MOR 1073), the remnant stump of the leftbasipterygoid process on the Sauropelta specimen(Figs. 11B, 15B; the only available example of a basiptery-goid process for Sauropelta) is relatively smaller than theright basipterygoid process on Tatankacephalus (Figs. 11A,15A). The remnant of the basipterygoid process on Sauro-pelta (YPM 5529) is not sufficient to determine whether itis fused or unfused to the quadrate process of the pterygoid,and thus within the current data matrix used here (Vickar-yous et al. 2004), the coding for this character is (?). Theventral surface of the basisphenoid between the basiptery-goid processes on Sauropelta (YPM 5529) is relativelysmooth and possesses a finely striated bilaterally symmetri-cal pattern, whereas the same surface on Tatankacephalus isirregularly rugose, especially at the base of the basipterygoidprocesses and exhibits no symmetrical patterning.

Fig. 15. Comparison of basipterygoid processes and ventral sur-faces of basisphenoids on Tatankacephalus cooneyorum gen. et sp.nov. (MOR 1073, holotype) and Sauropelta edwardsorum (YPM5529). (A) Ventral view of basisphenoid and right basipterygoidprocess on Tatankacephalus (MOR 1073). (B) Ventral view of ba-sisphenoid and remnant of left basipterygoid process on Sauropelta(YPM 5529). bpp, basipterygoid process; psr, parasphenoidal ros-trum; qrp, quadrate ramus of pterygoid. Photograph of YPM 5529courtesy of Yale Peabody Museum of Natural History.



LaterosphenoidThe foramina for the optic (II), oculomotor (III), trochlear

(IV), and abducens (VI) nerves emerge within depressionson the lateral surface of the laterosphenoid (Fig. 11A). Thelaterosphenoid continues dorsally to contact the skull roof.The laterosphenoid appears to merge with the postocularshelf, although the extent of the fusion between these twoelements cannot be determined due to damage.

Orbitosphenoid–presphenoidAlthough in some described ankylosaurids the interorbital

region comprises the presphenoid, orbitosphenoid, and sphe-nethmoid (Maryanska 1977), the demarcations betweenthese elements within the interorbital region are not clear.Within this region, four centimetres anterior to the foramenfor the optic nerve (II), there is an ovoid foramen that pier-ces the orbitosphenoid–presphenoid. This is either for theophthalmic artery or possibly a venous sinus. The orbitos-phenoid–presphenoid forms a wall that separates the orbitand forms the lateral margins of the channel for the olfac-tory nerve (I) (Vickaryous et al. 2004).

Parasphenoidal rostrumA robust subtriangular parasphenoidal rostrum projects

anteriorly from its junction with the basisphenoid (Fig. 10).It lies directly dorsal to the interpterygoid vacuity.

DentitionOne leaf-shaped tooth crown with multiple ridges on the

cusp was preserved with the holotype. It was found in thematrix that filled the left orbital cavity (Fig. 16). This toothis similar to the general structure of various ankylosaur max-illary or dentary teeth as described by Coombs (1990). It islabiolingually compressed and lacks any clear evidence of acingulum, a feature more commonly observed on the teethof ankylosaurids (Coombs 1990; Fig. 16). Between the basesof the basal denticles the mesial–distal dimension of thetooth is 8.94 mm; from the tip of the basalmost denticle tothe tip of the apical denticle the basal–apical dimension is10.24 mm. It is damaged along one edge. In buccal view, itis only slightly asymmetrical, exhibiting four denticles oneither side of the apical denticle. The apical denticle is bro-ken from the tooth but was found in contact with it and heldin position by the surrounding matrix. The apical denticle isapproximately the same size as the lateral denticles.

Although a considerable degree of variation in structurehas been observed on teeth from Sauropelta (Ostrom 1970;Coombs 1990; personal observation), the symmetrical set ofdenticles on the tooth of Tatankacephalus differs from theasymmetrical arrangement of denticles on the teeth of Sau-ropelta. There has been some abrasion to the enamel sur-face, but the ridges of the denticles and the fluting thatoccurs between the denticles clearly continue onto the crownface. This fluting does not continue down beyond the middleof the tooth. Similar fluting continues down to the cingulumon the teeth of Priconodon crassus (USMN 437985), a pos-sible nodosaurid from the Arundel Formation of Maryland(Carpenter and Kirkland 1998; personal observation). Alongwith the lack of a cingulum, the lack of the further extensionof this fluting differentiates the teeth of Tatankacephalusfrom those of Priconodon. The Arundel Formation and the

Cloverly Formation are of similar geological age; thus, de-spite the geographical separation, Priconodon is approxi-mately contemporaneous with Tatankacephalus andSauropelta.

Body osteodermsOnly two fragmentary osteoderms were recovered. The

intact osteoderm is large and oval in outline. It is 115 mmalong the short axis and 137 mm along its long axis(Fig. 17). It is hollow, asymmetrically spiked, conical, andthin-walled. Opposite to the position of the spike, the flattersurface of this oval is approximately 8 mm thick. The spikeitself is hollow. The internal surface of the osteoderm isconcave, and the edge of the osteoderm curves ventrallyand medially inward, undercutting the inner vacuity of thespike. The other osteoderm is incomplete. The hollow thin-walled structure of the complete osteoderm differs from themore solid osteoderms referred to Sauropelta (Ostrom 1970;personal observation) but still conforms to the general de-scription of osteoderms in Sauropelta (Ostrom 1970). It isalso similar to those described in Mymoorapelta (Kirklandet al. 1998). The anatomical positions of these two osteo-derms cannot be determined.

Rib fragmentsSeveral mid-section rib fragments with ovoid cross-sec-

tions were recovered. No other details are apparent.

Phylogenetic relationships

The phylogenetic position of Tatankacephalus cooneyo-rum within Ankylosauria was assessed by a cladistic analy-

Fig. 16. Photograph and illustration of maxillary or dentary tooth ofTatankacephalus cooneyorum gen. et sp. nov. (MOR 1073, holo-type).

Fig. 17. Fragmentary (dorsal?) osteoderm of Tatankacephalus coo-neyorum gen. et sp. nov. (MOR 1073, holotype). (A) External sur-face. (B) Internal surface.



sis of 26 taxa (24 ingroup ankylosaur taxa and two outgrouptaxa) and 63 characters, taken primarily from Vickaryous etal. (2004) and Osi (2005). Outgroup taxa included Huayan-gosaurus (Vickaryous et al. 2004) and Scelidosaurus (Osi2005). The scorings for Hungarosaurus, Scelidosaurus, andStruthiosaurus were taken from Osi (2005). The Struthiosau-rus characters that were taken by Osi (2005) came fromthree species, S. austriacus, S. transylvanicus, and S. langue-docensis. The data matrix included 63 characters: 53 werebinary and 10 were multistate. All 63 characters weretreated as unordered and of equal weight. For the purposeof creating a Bremer support analysis, secondary cladisticanalyses were run retaining suboptimal trees up to threesteps out. A Nexus data file was constructed using NexusData Editor, Version 0.5.0 (Page 2001). The data matrixwas analyzed using TNT version 1.0 (Goloboff et al. 2005).The swapping algorithm chosen was tree bisection reconnec-tion (TBR), which is the default setting. Default settingswere also chosen for the number of replications and the trees(10) saved per replication. The most parsimonious trees pos-sessed branch-length best scores of 170 steps. The best scorewas hit two times out of ten. There were 20 trees retained.The characters for Tatankacephalus can be found in Table 1.The consistency index (CI) was 0.447 and the retention in-dex (RI) was 0.713. This strict consensus tree was generatedwithin a TNT (traditional) heuristic analysis (Fig. 18).

Most of the scorings were retained from the analysis ofVickaryous et al. (2004), but there have been some changes.

Beyond the establishment of a new taxon, one other result ofthis study has been a re-examination of the cranial elementsof Sauropelta edwardsorum. This has led to re-evaluation ofsome of the cranial characters coded in the data matrix byVickaryous et al. (2004) In regard to AMNH 3035, the cra-nial roof in lateral profile posterior to the orbit is flat (char-acter 3), so the code for this character has been changed to(0). The character code for the fused or unfused nature ofthe contact between the quadrate process of the pterygoidand the basipterygoid processes (Character 30) has beenchanged to (?). The fusion between the quadrate and paroc-cipital process (character 39) is evident on AMNH 3035;thus, the coding for this character has been changed to (1).With the observation of a postocular shelf on the skull ofPanoplosaurus (ROM 1215; personal observation), the cod-ing for this character on this taxon has been changed to (1).Rows of coossified fused cervical osteoderms (character 49)have been reported in Scelidosaurus by Carpenter et al.(2001). Character 49 from Osi (2005) relating to Scelidosau-rus has been re-coded as (1). For Gastonia (J. Kirkland, per-sonal communication, 2008), the basipterygoid process isnot fused to the quadrate ramus of the pterygoid, and char-acter 30 has been re-coded as (1).

Results

The following definitive statements can be made regard-ing the results of this cladistic analysis.

Table 1. Cladistic characters and character states for Tatankacephalus cooneyorum gen. et sp. nov., and the exactsame characters taken from Osi (2005) for Scelidosaurus harrisonii and Struthiosaurus (composite of three spe-cies) 1–63 from Vickaryous et al. (2004).

Huayangosaurus 0000000010 000000000? ?00000000? 1000000100 00000??000 00?010?00? 000Scelidosaurus 0000000000 0000??0010 00??0????? 1??????0?0 ?001111?10 000000000? 000Tatankacephalus 0110122??1 11?1?20001 111??11010 1001?11?1? 111??????? ?????????? ?11Gargoyleosaurus 0000022101 1010100000 010000101? ??0?0??010 ?1111???11 ?????????? ?01Cedarpelta 0?01111?00 0?0??010?? ??1???000? ?0?100?000 ?11?1????1 ??????0??? ?11Pawpawsaurus 0010122111 1000000110 00000?0100 1001100010 ?11??????? ?????????? ?11Hungarosaurus ???02?1?0? ??0?11001? 0?0????0?? ????0??0?? ???11?1121 030??10??? 11?Edmontonia rugosidens 0010101411 0000011111 100001110? ?10111?010 0111111111 ??1??????? 111Silvisaurus 0110101101 0000000011 0000??0101 100?100011 ?111??1011 ?????????0 1?1Sauropelta 0000101??1 00??????1? ?????????? ?001110010 ??1110?0?1 0300111?1? ???Panoplosaurus 0010001411 100001111? 1?00??010? ?101101010 111111??11 0300?11?10 111Minmi 0001122??0 ?0?012?01? ???????0?? 1?000001?? ?11??????1 ???0??0?1? ??1Euoplocephalus 1101222200 1111121101 2111111111 1111011101 111110?121 11112101?0 101Ankylosaurus 1101222210 1111121001 210?110111 1111011111 11111?11?1 11?1?10??? ?11Gastonia 0100022101 101112100? 10100??111 10100111?0 ?11?????21 ?2?1111??? 101Gobisaurus 0001011100 0001121011 2011?11011 110?011110 111??????? ?????????? ?01Pinacosaurus grangeri 1001222??0 ?111121011 2111111010 1110010101 1111102121 1201210111 101Saichania 1001222300 1111121011 2111111010 1111011111 1111?12121 12?1210111 101Shamosaurus 1001211200 10001210?1 2011??0010 ?1??01?110 11111???21 ?211????1? ?01Tarchia 1001222300 1111121011 2111?11011 1111011?01 11111??0?1 12?121011? ?01Talarurus ?0012222?0 11???????? ?????11?10 110101??0? 111?1?2121 12?1210111 1??Tianzhenosaurus 1001222310 1110?210?? ??10???010 0010011101 ?11??0?1?1 1???1?0??? 101Tsagantegia 0001121100 1111121011 2?11?10011 0111011111 111??????? ?????????? ?01Ed. longiceps 0010101411 000001111? 100001110? ?10111?010 011111??11 ?????????? 111Pinacosaurus mesphistoce 1011222??0 1111021?1? ?111?1???? ?????1???1 ?1111??121 1??11???1? 101Struthiosaurus ??10000??1 00???????? ?????????? ??01000110 ??1??0012? ?3?0?1010? 1??

Note: Scelidosaurus is presented as one of the outgroup taxa. There are corrections in regard to characters 3, 30, 39, 41, and49 (see text).



(1) Tatankacephalus is a member of Ankylosauridae.(2) Hungarosaurus, Gargoyleosaurus, and Struthiosaurus

are not supported as members of either Ankylosauri-dae or Nodosauridae and have been positioned as ba-sal ankylosaurs.

(3) Within the Bremer support analysis, there is some sup-port for a pairing of Tatankacephalus and Gastonia.They are united for trees at least two steps longer.Although Tatankacephalus is distinct from Gastoniain that it possesses certain characters such as a su-praorbital boss, a fused basipterygoid process withquadrate ramus of the pterygoid, a dome-like cranialroof posterior to the orbit (in lateral view), ornamenta-tion of the premaxilla, and a nuchal shelf that over-hangs the occiput, Gastonia and Tatankacephalusshare several characters that unite them as sister taxa.These include

(4) In lateral profile anterior to the orbit, the cranial roofis dome-like.

(5) The squamosal boss is a pyramidal protuberance.(6) The quadratojugal projection is a deltaic protuberance.(7) Raised nuchal sculpting is present.(8) The maximum premaxillary rostrum width is equal to

or greater than the distance between the posteriormostmaxillary teeth.

(9) The premaxillary tomia continues posteriorly and islateral to the maxillary tooth row.

(10) The maxillary tooth rows are linear anteriorly and di-verge posteriorly.

(11) Maxillary and dentary cingula are absent.(12) The secondary palate comprises only the anterodorsal

palatal arch.(13) The external naris are visible in anterior view.(14) The mandibular ramus of the pterygoid is directed

anterolaterally.(15) The basisphenoid length is less than that of the basioc-

cipital.(16) The basal tubera structure is bulbous.(17) The paroccipital processes are directed laterally.(18) The occipital condyle is oriented posteroventrally.(19) The foramen magnum is oriented posteroventrally.(20) The alternative hypothesis of Polacanthidae as a sepa-

rate major clade within Ankylosauria is not supported.(21) Ankylosauridae and Nodosauridae still appear as

monophyletic clades within Ankylosauria.(22) The analysis places Pinacosaurus grangeri and P. me-

phistocephalus as part of a polytomy; this does not ne-cessarily mean that they are not closely related to oneanother, rather that the interrelationships of deeplynested ankylosaurids are unresolved.

The Bremer support analysis demonstrates that the rela-tionships among many ankylosaurs are poorly resolved.Thus, there is a need for a much more robust phylogeneticanalysis of Ankylosauria. Such an extensive cladistic analy-sis could not be conducted without a prior review of all ac-tual material from all collections relating to recognized taxawithin Ankylosauria, and thus it would be beyond the scopeof this current description of a new taxon.

DiscussionThe phylogenetic analysis reveals that this taxon is in a

transitional position between the more basal ankylosauriansand the Late Cretaceous ankylosaurids. This finding is sig-nificant because it provides important new character datafor the transition to the typical Late Cretaceous ankylosaur-ids that have tended to characterize perceptions of the clade.Some defining features in Tatankacephalus, such as the twosets of bosses, the curvature of the cranial profile anteriorfrom the orbit, the paranasal sinuses, and the overhangingnuchal ridge that obscures the occiput are similar to farmore pronounced features in later members of Ankylosauri-dae, such as Euoplocephalus and Ankylosaurus.

BraincaseFigures 11A and 11B present comparisons of the lateral

surfaces of the braincase regions on Tatankacephalus (MOR1073) and Sauropelta (YPM 5529). In Fig. 11A, the internalcarotid artery foramen on MOR 1073 is a slightly dorsoven-trally flattened oval, while the comparable foramen on YPM

Fig. 18. Phylogenetic relationships of Ankylosauria based on aheuristic (traditional) analysis of 25 taxa and 63 characters takenfrom Vickaryous et al. (2004) and Osi (2005) using TNT version1.0 (Goloboff et al. 2005) software. From 307 578 tree arrange-ments, a strict consensus tree was generated with consistency index(CI) equaling 0.447 and retention index (RI) equaling 0.713.Twenty trees retained. Best score tree length 170. Major clades la-beled in smaller bold script and indicated by thick vertical lines.Numbers above branches are Bootstrap support values; numbersbelow branches are Bremer support values. In Bremer support sym-bol ‘+’ represents ‘‘more than.’’ Bootstrap resampling output op-tions were set to ‘‘absolute frequencies,’’ and the number ofreplicates compared was 10 000. Only Bootstrap values above 50%shown.



5529 (Fig. 11B) is a relatively larger, anteroposteriorly flat-tened oval. Similar contrasts in the long axes of the oval tri-geminal nerve foramina (V) exist. For MOR 1973, the longaxis of the oval trigeminal nerve foramen (Fig. 11A) is ante-roposterior in orientation. For YPM 5529, the long axis ofthe oval trigeminal nerve foramen (Fig. 11B) is dorsoventralin orientation. On MOR 1073, the breakage at the base ofthe left basipterygoid process (Fig. 11A) indicates that theprocess was a much more robust feature than the basal tu-bercle. On YPM 5529, the basal tubercle (Fig. 11B) appearsequal to or possibly even larger than the basipterygoid proc-ess. On MOR 1073, the facial nerve foramen (VII)(Fig. 11A) appears on a laterally enlarged prominence di-rectly above the internal carotid foramen and is separatedfrom it by the enlarged dorsal rim of the internal carotidforamen. In contrast, on YPM 5529 (Fig. 11B), althoughthe facial nerve foramen appears in roughly the same posi-tion relative to the internal carotid artery foramen as onMOR 1073, it is within a recessed concavity that ventrallycontinues into a trough between the ventral edge of the fa-cial nerve foramen and the dorsal edge of the internal caro-tid foramen. On YPM 5529, the cranial foramina in thelaterosphenoid region (Fig. 11B) open in a more anteriorlyoriented direction than on MOR 1073 (Fig. 11A). Althoughthe cranial nerves in this region are in comparable positions,in general the laterosphenoid on YPM 5529 (Fig. 11B) ap-pears anteroposteriorly more compressed.

HomoplasyBetween the two primary clades of Ankylosauria, there is

a considerable degree of apparent homoplasy; this may havecontributed to the lack of resolution in the more weakly sup-ported branches within this latest cladistic analysis. Exam-ples of features that occur as apparent examples ofhomoplasy are the presence of a parietal dome; a postocularshelf; a pyramidal, laterally projecting postorbital boss; atransversely aligned, continuous, laminar posterior edge tothe pterygoids (this character is plesiomorphic with the pter-ygoid structure of the holotype skull of Stegosaurus stenops(USNM 4934; personal observation)); the development oforbital rings; and the retention of a visible lateral temporalfenestra. The resolution of either the homoplastic or homol-ogous origin of these features would add considerably to ourunderstanding of the relationships between the taxa withinAnkylosauria.

AcknowledgementsWe express our sincerest thanks to J.P. Cooney and J.P.

Cooney, Jr. and are indebted to J. Horner for the years ofencouragement he has given to us. Also, we thank R. Laubof the Buffalo Museum of Science for his friendship, in-struction, and continuous encouragement in all aspects ofthis project. We acknowledge the advice, support, and en-couragement received from C. Ancell, R. Harmon, P.Leiggi, D. Varricchio, and the Museum of the Rockies. Wethank L. Witmer and H. Rockhold for the CT scan, L.Witmer for having proofread the initial draft of this text,and V. Martonis for copy-editing the final drafts. We thankJ. Grehan of the Buffalo Museum of Science for advice incladistic analysis. K. Carpenter, J. Kirkland, and S. Samp-son, gave continued advice and encouragement. We thank

the following for access to specimens and in some cases theuse of photographs of these specimens: H.-D. Sues, T. Carr,and K. Seymour (ROM); M. Norell, C. Mehling, and C.Holton (AMNH); and J. Gauthier, W. Joyce, D. Brinkman,and L. Murray (YPM). We thank P. Bush from the Univer-sity of Buffalo. We thank M. Sorenson for help with thecladistic analysis. We would like to thank H.-D. Sues, theAssociate Editor of the Canadian Journal of Earth Sciencesand our two anonymous reviewers for their insightful cri-tiques. Finally, we would like to acknowledge our indebted-ness to J. Ostrom for having initially encouraged us whenwe needed it.

ReferencesBarrett, P.M., You, H., Upchurch, P., and Burton, A.C. 1998. A

new ankylosaurian dinosaur (Ornithischia: Ankylosauria) fromthe Upper Cretaceous of Shanxi Province, People’s Republic ofChina. Journal of Vertebrate Paleontology, 18: 376–384.

Brown, B. 1908. The Ankylosauridae, a new family of armored di-nosaurs from the Upper Cretaceous. Bulletin of the AmericanMuseum of Natural History, 24: 187–201.

Carpenter, K. 2004. Redescription of Ankylosaurus magniventrisBrown, 1908 (ankylosauridae) from the Upper Cretaceous ofthe Western Interior of North America. Canadian Journal ofEarth Sciences, 41(8): 961–986. doi:10.1139/e04-043.

Carpenter, K., and Kirkland, J.I. 1998. Review of lower and middlecretaceous ankylosaurs from North America. In Lower and Mid-dle Cretaceous terrestrial ecosystems. Edited by S.G. Lucas, J.I.Kirkland, and J.W. Estep. New Mexico Museum of Natural His-tory and Science, Bulletin No. 14, pp. 249–270.

Carpenter, K., Miles, C., and Cloward, K. 1998. Skull of a Jurassicankylosaur (Dinosauria). Nature, 393(6687): 782–783. doi:10.1038/31684.

Carpenter, K., Kirkland, J.I., Burge, D., and Bird, J. 2001. Disarti-culated skull of a new primitive ankylosaurid from the LowerCretaceous of eastern Utah. In The Armored dinosaurs. Editedby K. Carpenter. Indiana University Press, Bloomington, Ind.,pp. 211–238.

Coombs, W.P., Jr.. 1978. The families of the ornithischian dinosaurorder Ankylosauria. Palaeontology, 21: 143–170.

Coombs, W.P., Jr. 1990. Teeth and taxonomy in ankylosaurs; InDinosaur systematics: approaches and perspectives. Edited byK. Carpenter and P. Currie. Cambridge University Press, NewYork, N.Y., pp. 269–279.

Coombs, W.P., Jr., and Maryanska, T. 1990. Ankylosauria; In TheDinosauria. Edited by D.B. Weishampel, P. Dodson, and H. Os-molska. University of California Press, Berkeley, Calif.,pp. 456–483.

Forster, C.A. 1990. The postcranial skeleton of the ornithopod di-nosaur Tenontosaurus tilletti. Journal of Vertebrate Paleontol-ogy, 10: 273–294.

Goloboff, P., Farris, J.S., and Nixon, K. 2005. T.N.T.: Tree Analy-sis Using New Technology version 1.0, Program and documen-tation available from the authors and at www.zmuc.dk/public/phylogeny.

Harris, J.D. 1998. A Reanalysis of Acrocanthosaurus atokensis, itsphylogenetic status, and paleobiogeographic implications, basedon a new specimen from Texas. New Mexico Museum of Nat-ural History and Science, Bulletin 13, Albuquerque, New Mex-ico, 75 p.

Jacobs, L.L., Winkler, D.A., Murry, P.A., and Maurice, J.M. 1994.A nodosaurid scuteling from the Texas shore of the Western In-terior Seaway. In Dinosaur eggs and babies. Edited by K. Car-



penter, K.F. Hirsch, and J.R. Horner. Cambridge UniversityPress, New York, N.Y., pp. 337–346.

Kilbourne, B., and Carpenter, K. 2005. Redescription of Gargoy-leosaurus parkpinorum, a polacanthid ankylosaur from theUpper Jurassic of Albany County, Wyoming. Neues Jahrbuchfur Geologie und Palaontologie. Abhandlungen, 237: 111–160.

Kirkland, J.I. 1998. A polacanthine ankylosaur (Ornithischia: Dino-sauria) from the Early Cretaceous (Barremian) of Eastern Utah.In Lower and Middle Cretaceous terrestrial ecosystems. Editedby S.G. Lucas, J.I. Kirkland, and J.W. Estep. New Mexico Mu-seum of Natural History and Science Bulletin 14, pp. 271–281.

Kirkland, J.I., Carpenter, K., Hunt, A.P., and Scheetz, R.D. 1998.Ankylosaur (Dinosauria) specimens from the Upper JurassicMorrison Formation. Modern Geology, 23: 145–177.

Kvale, E.P., and Vondra, C.F. 1993. Effects of relative sea-levelchanges and local tectonics on a Lower Cretaceous fluvial totransitional marine sequence. Bighorn Basin, Wyoming, USA.Special Publication of the International Association of Sedimen-tologists, 17: 383–399.

Lee, Y.-N. 1996. A new nodosaurid ankylosaur (Dinosauria: Or-nithischia) from the Paw Paw Formation (late Albian) of Texas.Journal of Vertebrate Paleontology, 16: 232–245.

Makovicky, P.J., and Sues, H.-D. 1998. Anatomy and phylogeneticrelationships of the Theropod Dinosaur Microvenator celer fromthe Lower Cretaceous of Montana. American Museum Novitates3240, pp. 1–27.

Maryanska, T. 1977. Ankylosauridae (Dinosauria) from Mongolia.Palaeontologia Polonica, 37: 85–151.

Molnar, R.E. 2001. Armor of the Small Ankylosaur Minmi; In TheArmored Dinosaurs. Edited by K. Carpenter. Indiana UniversityPress, Bloomington, Ind., pp. 341–362.

Nopcsa, F. 1915. Die dinosaurier der siebenburgischen landesteileungarns. Mitteilungen aus dem Jahrbuche der Koniglich. Ungar-ischen Geologischen Reichsanstalt, 23: 1–26.

Osborn, H.F. 1923. Two Lower Cretaceous dinosaurs from Mongo-lia. American Museum Novitates 95, pp. 1–10.

Osi, A. 2005. Hungarosaurus tormai, a new ankylosaur (Dino-sauria) from the Upper Cretaceous of Hungary. Journal of Verte-brate Paleontology, 25(2): 370–383. doi:10.1671/0272-4634(2005)025[0370:HTANAD]2.0.CO;2.

Ostrom, J.H. 1969. Osteology of Deinonychus antirrhopus, an unu-sual theropod from the Lower Cretaceous of Montana. Bulletinof the Peabody Museum of Natural History, 30, pp. 1–165.

Ostrom, J.H. 1970. Stratigraphy and paleontology of the cloverlyformation (lower cretaceous) of the Bighorn basin area, Wyom-

ing and Montana. Bulletin of the Peabody Museum of NaturalHistory, 35, 1–234.

Owen, R. 1842. Report on British Fossil Reptiles. Part II. Reportsof the British Association for the Advancement of Science, 11:60–204.

Page, R.D.M. 2001. Nexus Data Editor, version 0.5.0. ComputerProgram available at http://taxonomy.zoology.gla.ac.uk/rod/NDE/nde/html.

Pang, Q.-Q., and Cheng, Z.-W. 1998. A new ankylosaur of LateCretaceous from Tianzhen, Shexi. Progress in Natural Science,8: 326–334.

Russell, L.S. 1940. Edmontonia rugosidens (Gilmore), An armoreddinosaur from the Belly River series of Alberta. University ofToronto Studies Geological Series, University of Toronto Press,Toronto, Ont., Canada, Vol. 43, pp. 1–15.

Seeley, H.G. 1887. On the classification of the fossil animals com-monly named Dinosauria. Proceedings of the Royal Society ofLondon, 43(1): 165–171. doi:10.1098/rspl.1887.0117.

Sereno, P.C. 1999. The evolution of dinosaurs. Science, 284(5423):2137–2147. doi:10.1126/science.284.5423.2137.

Tumanova, T.A. 1987. Sovmestnaya Sovetsko-Mongol’skaya Pa-leontogichekaya Ekpeditsiya [The armored dinosaurs of Mongo-lia]. Trudy, 32: 1–80.

Tumanova, T.A. 1993. A new armored dinosaur from southeasternGobi. Paleontological Journal, 27: 119–125.

Vickaryous, M.K., and Russell, A.P. 2003. A redescription of theskull of Euoplocephalus tutus (Archosauria: Ornithischia): afoundation for comparative and systematic studies of ankylo-saurian dinosaurs. Zoological Journal of the Linnean Society,137(1): 157–186. doi:10.1046/j.1096-3642.2003.00045.x.

Vickaryous, M.K., Russell, A.P., Currie, P.J., and Zhao, P.J. 2001.A new ankylosaurid (Dinosauria: Ankylosauria) from the LowerCretaceous of China, with comments on ankylosaurian relation-ships. Canadian Journal of Earth Sciences, 38(12): 1767–1780.doi:10.1139/cjes-38-12-1767.

Vickaryous, M.K., Maryanska, T., and Weishampel, D.B. 2004.Ankylosauria. In The Dinosauria. 2nd ed. Edited by D.B.Weishampel, P. Dodson, and H. Osmolska. The University ofCalifornia Press, Berkeley, Calif., pp. 363–392.

Witmer, L.M., and Ridgely, R.C. 2008. The Paranasal Air Sinusesof Predatory and Armored Dinosaurs (Archosauria: Theropodaand Ankylosauria) and Their Contribution to Cephalic Structure.The Anatomical Record, 291(11): 1362–1388. doi:10.1002/ar.20794.



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