A juvenile skull of the tyrannosaurid Tarbosaurus bataar found in the Bugjn Tsav locality in the Mongolian Gobi Desert is described. With a total length of 290 mm, the present specimen represents one of the smallest skulls known for this species. Not surprisingly, it shows various characteristics common to juvenile tyrannosaurids, such as the rostral margin of the maxillary fenestra not reaching that of the external antorbital fenestra and the postorbital lacking the cornual process. The nasal bears a small lacrimal process, which disappears in adults. Lacking some of the morphological characteristics that are adapted for bearing great feeding forces in adult individuals, this juvenile specimen suggests that T. bataar would have changed its dietary niches during ontogeny. The numbers of alveoli in the maxilla (13) and dentary (14 and 15) are the same as those in adults, suggesting that they do not change onto genetically in T. bataar and thus are not consistent with the hypothesis that the numbers of alveoli decreases ontogenetically in tyrannosaurids.

A new species of the cythaspid Poraspis is described from the Emsian (Early Devonian) Lippincott Member of the Lost Burro Formation in Death Valley, California. Poraspis thomasi, sp. nov., extends the geographic range of the genus, which had previously been reported from western Europe, Spitsbergen, the Canadian Arctic Archipelago, and District of Mackenzie. In addition, the temporal range is extended as the previously described species ranged through the Late Silurian into the Pridoli. This species includes articulated specimens showing that the oral area consisted of a single rectangular oral plate, in contrast with the view that in cyathaspids the area consisted of an arrangement of numerous finger-like plates. Also, one ventral shield shows growth lines indicating that growth of the shield occurred in a posterior direction. An additional poraspid, Lechriaspis patula, gen. et sp. nov., is described from a single specimen from the Grassy Flat Member of the Water Canyon Formation, northern Utah, that shows evidence of puncture wounds indicating predation by a eurypterid. These new heterostracans represent the first true cyathaspids to be described from the Devonian of the western United States.

The acanthothoracid Hagiangella goujeti Janvier, 2005, has been described exclusively on the basis of isolated thoracic plates from the Lochkovian (Lower Devonian) Khao Loc Formation of Tung Vai, Ha Giang Province, northern Vietnam. It is characterized by a very high, triangular median crest on the median dorsal plate, and has been referred to the Acanthothoraci on the basis of the morphology of its fused anterolateral, spinal and anterior ventrolateral plates, and the characteristic stellate ornamentation of the group. Isolated plates of H. goujeti are relatively abundant at Tung Vai and no other placoderm taxon from this locality seems to share the same type of ornamentation. However, the skull of this species remained elusive. Here we report two well-preserved skull roofs from Tung Vai, which we refer to H. goujeti. They display the same stellate ornamentation and small size as the previously described plates of the thoracic armor of this species. This new material shows that the head of H. goujeti is surprisingly short (i.e., possibly lacking dermal rostral and pineal elements), in contrast to the elongate and narrow skull of all other acanthothoracids. The combination of unique characters (e.g., presence of two pairs of posterior pit lines, two pairs of central and paranuchal plates, etc.) suggests a possible sister group relationship to the placoderm assemblage Petalichthyida Ptyctodontida Arthrodira.

Vertebrate fossils have been known from South India's Cauvery Basin since the 1840s, but records of marine vertebrates from the late Albian to Turonian Karai Formation have been limited to a single set of ichthyosaur remains. Recent surface collecting and sieving of lower Cenomanian glauconitic mudstones has yielded the first ichthyosaur material reported in India over the last 140 years, as well as a diverse and previously unrecorded shark assemblage. The ichthyosaur material, including several teeth and vertebrae, is assigned to the sole described Cretaceous genus Platypterygius and to the species P. indicus (Lydekker, 1879). Eight species of shark (one squaliformes, two hexanchiformes, and five lamniformes) are recorded. A new hexanchiform genus Gladioserratus is erected, and two new species (Gladioserratus magnus, gen. et sp. nov., and Dwardius sudindicus, sp. nov.) are named. Many of the shark genera within this largely species-level endemic fauna are known from high paleolatitudes elsewhere, with many showing an antitropical distribution, but are absent in Tethyan areas. This first description of the Karai Formation marine fauna documents the previously unappreciated diversity and unique character of India's Cretaceous marine vertebrates, and indicates a cool-water paleoenvironment for the marine vertebrate assemblage.

Plicidentine, infolded dentine around the pulp cavity at the base of a tooth, has been histologically characterized in sarcopterygians, basal tetrapods, and the actinopterygian Lepisosteus. Within amniotes, however, its phylogenetic distribution is much less well documented and its morphological variability has not been described, in spite of the fact that plicidentine is considered a synapomorphy of three major clades of amniotes (Neochoristodera, Ichthyosauria, and Varanoidea). In this study, we provide a summary of the taxonomic distribution of plicidentine in amniotes, and also describe the morphological variation encompassed by this term. We conclude that plicidentine, as defined here, has evolved independently several times in amniotes, and that each occurrence is histologically distinct.

The taxonomy and systematics of the earliest plesiosaurians is poorly resolved. This limits our understanding of the diversification of one of the most successful clades of secondarily aquatic tetrapods. Here we provide a robust diagnosis of Thalassiodracon hawkinsii from the Pre-planorbis Beds (Triassic—Jurassic boundary interval) of the United Kingdom, and suggest that at least two other, previously unrecognized plesiosaurians are present in the same deposits. Computed tomography of an exceptionally preserved skull, and examination of previously undescribed (or briefly described) specimens yields new anatomical data. Thalassiodracon has a dorsomedian ridge on the premaxilla, a squamosal bulb, four premaxillary teeth, and a heterodont maxillary dentition. Several features of Thalassiodracon, including the squmosal bulb, broad anterior termination of the pterygoids, heterodont dentition, and single foramen in the lateral surface of the exoccipital, are plesiomorphic or represent pliosauroid synapomorphies. Among pliosauroids, Thalassiodracon shares a parietal that extends far anteriorly, a broad, interdigitating posterior termination of the premaxilla, and a short posteroventral process of the postorbital with Hauffiosaurus and pliosaurids. Thus, we suggest pliosaurid affinities for Thalassio dracon, in contrast to most recent phylogenetic studies. The early stratigraphic position of Thalassiodracon coincides with the earliest occurrence of Rhomaleosauridae (the sister taxon of Pliosauridae). The relatively long neck and small skull of Thalassiodracon indicate that the robust skeleton and macropredaceous habits of rhomaleosaurids and pliosaurids were derived independently.

Graptemys kerneri, n. sp., from the Suwannee River drainage of north-central Florida, represents the most southeastern occurrence of the genus. This species is morphologically and geographically most similar to the extant Barbour's map turtle, Graptemys barbouri. G. kerneri exhibits sexual dimorphism similar to extant G. barbouri, G. ernsti, G. pulchra, and G. gibbonsi, with females being megacephalic and attaining a much larger size than males. The new species possesses a very wide skull and mandible, making it the most blunt-headed member of its clade. Specimens described here include a nearly complete skull, eight mandibles, two epiplastra, 34 neural bones, and an assortment of other shell fragments. Previously reported fossil material from Florida was collected in the 1960s along the Santa Fe River and referred to both the Pliocene and Pleistocene. Rare earth element (REE) analysis of this material is reinterpreted here as being Rancholabrean in age.

We report the discovery of a new species of the snake Madtsoia from1 infratrappean horizons of Late Cretaceous age in Pisdura, central India. Recovered vertebrae are large (1.83 cm long; 4.35 cm tall) and pertain to a snake that was ca. 5 m long. Discovery of Madtsoia in India extends the geographic distribution of the genus and represents only the second species known from the Cretaceous. Vertebrae of Madtsoia pisdurensis sp. nov. are strikingly similar to those of M. bai and M. camposi (South America) and M. madagascariensis (Madagascar), but can be distinguished from them by a unique process on the hemal keel, which is low, flat, and triangular in outline. Whereas the eastern Gondwanan species of Madtsoia (M. madagascariensis, M. pisdurensis) are Late Cretaceous in age, the western Gondwanan species (M. bai, M. camposi) are Paleogene in age. Geophysical evidence suggests that land connections between South America, Madagascar, and Indo-Pakistan were severed by at least 100–90 Ma, which implies that Madtsoia achieved its broad geographic distribution either by (1) origin and dispersion before the end of the Turonian; or (2) the presence of an unrecognized land connection persisting into the latest Cretaceous. Both hypotheses predict that Madtsoia will be discovered in Mesozoic strata of South America, where it survived the Cretaceous-Paleogene mass extinction.

The South American record of early Late Triassic aetosaurs is composed of two species: Aetosauroides scagliai and “Aetosauroides subsulcatus.” Previously undescribed materials belonging to “Aetosauroides subsulcatus” allow us to reassess its taxonomy, leading us to consider it a junior synonym of Aetosauroides scagliai. Based on the emended diagnosis of the species provided here, we recognize that specimens assignable to Aetosauroides scagliai are less common than thought previously and several of them are not diagnostic beyond indeterminate non-typothorasicine aetosaurins. Previous assignments of Aetosauroides as a junior synonym of Stagonolepis are not followed because the South American taxon is distinct due to the presence of a maxilla excluded from the external narial margin, tooth crowns with a straight distal margin and without a constriction between the root and crown, a gradually convex ventral margin of the dentary, oval fossae ventral to the neurocentral suture on the lateral sides of the centra, and a ratio between the length and the width between the distal-most tips of the postzygapophyses equal to or lower than 0.75. The evidence provided here bolsters the validity of Aetosauroides and extends the distribution of Aetosauroides scagliai into southern Brazil. Although Stagonolepis was employed as an index taxon for the Adamanian LVF, this genus is currently restricted to Europe and North America. Thus, no overlapping genera or species of aetosaur are shared between South America and other landmasses. Accordingly, the record of aetosaurs is not useful for providing biostratigraphical correlations between Late Triassic South American beds and those in other regions.

A new basal sauropodornorph dinosaur, Arcusaurus pereirabdalorum, sp. nov., is named and described on the basis of a partial, disarticulated but associated skull and dispersed cranial and postcranial elements from at least two individuals. Arcusaurus is part of a distinctive local fauna from the upper Elliot Formation (Lower Jurassic) in the Senekal District, Free State, South Africa. It can be diagnosed by various details of the premaxilla, nasal, and dentary in the skull and the shape of the distal caudal vertebrae. The taxon displays an unusual mix of characteristics. It lacks several synapomorphies of Plateosauria (Phteosaurus Massospondylus and all descendants of their most recent common ancestor) but does display other derived characteristics that are otherwise known only from less inclusive clades within Plateosauria. In a cladistic analysis a position outside Plateosauria as the sister group of the clade of Efraasia more-derived sauropodomorphs is supported; however, this position was not found to be a significantly better explanation of the data as a relatively derived position within Plateosauria. If the basal position for Arcusaurus is accepted, then a divergence from other sauropodomorphs in the middle Norian and a ghost lineage up to 35 Ma is implied. No other non-plateosaurian sauropodomorphs are known from the Jurassic, making Arcusaurus a potentially relictual taxon in the Early Jurassic.

Basal ornithopods exhibit a very low diversity in Cretaceous deposits of Asia, with only two diagnostic taxa published to date. A new basal ornithopod, Haya griva, gen. et sp. nov., is described here based on several well-preserved specimens from the Late Cretaceous Javkhlant Formation of Mongolia. Haya is diagnosed by a unique combination of characters, some of which are also present in other Asian Cretaceous basal ornithopods such as a bifid caudal ramus of the jugal and a tapering and beveled predentary. Traits, such as presence of separate maxillary fenestra, otherwise only known in Hypsilophodon, show more homoplastic distributions. Phylogenetic analysis provides weak support for grouping Haya with the Chinese Cretaceous taxa Jeholosaurus and Changchunsaurus, suggesting a greater hidden diversity of such animals in Asia. The most complete prepared specimen of Haya exhibits a sizeable gastrolith mass, representing only the second occurrence among ornithopods.

Sexual dimorphism, the condition whereby males and females differ from one another physically, is one of the most fundamental aspects of the biology of any animal. However, sexually dimorphic characters can be subtle and are mainly related to soft tissue anatomy. They are, therefore, difficult to identify reliably in the fossil record particularly when dealing with small sample sizes and osteology alone. The first geometric morphometric analysis of dimorphism in a thyreophoran (armored) dinosaur shows that the femora of the stegosaurian dinosaur Kentrosaurus aethiopicus (Upper Jurassic, Tanzania) bear a statistically significant shape difference of the proximal end, which is independent of size and is therefore proposed to be a sexual difference. Although the disarticulated nature of the material means that intraspecific variation in other skeletal elements, such as the enigmatic dermal armor, cannot be identified as sexual dimorphism at this time, this study provides a methodology for further work on articulated stegosaurian specimens and has the potential to reveal additional information regarding the paleobiology and population dynamics of this poorly understood clade.

Fossils of pelagornithids (bony-toothed birds) have been reported from strata of Paleocene to Pliocene age, and from every continent. The extreme fragility of pelagornithid bones has no doubt contributed to their geographically and temporally sporadic record, and thus it has been difficult to appreciate any long-term phylogenetic trends through geologic time for this group. We report a well-preserved partial humerus of the gigantic bird Pelagornis from the late Neogene Purisima Formation of central California. Due to its incompleteness, we refrain from naming a new species. This fossil is fortuitously bracketed by two ash beds, which have been correlated with volcanic rocks at 3.35 ± 0.05 Ma and 2.5 ± 0.2 Ma, indicating a middle to late Pliocene age for this fossil. This fossil extends the record of the pelagornithids in the Northeast Pacific, previously only known up until the early late Miocene (10–12 Ma). This fossil is the latest record of a pelagornithid for the Pacific Basin, and additionally represents the latest reliably dated pelagornithid record worldwide. This record suggests that the pelagornithids survived until the end of the Pliocene, and became extinct during the ocean restructuring and climatic upheavals that caused the demise of many other groups of marine vertebrates at that time.

The morphology of the labyrinth of zhelestids, a group of eutherian mammals from the Late Cretaceous, agrees with that of other extinct eutherians, including Kulbeckia kulbecke, Ukhaatherium gobiensis, and Zalambdalestes lechei. Features of the labyrinth of zhelestids include a cochlea with one and a half turns and a secondary common crus, which are plesiomorphic for eutherians. Although isolated petrosals likely represent multiple species because several species of zhelestids are recognized based on dental characters, the degree of variation within the entire zhelestid petrosal sample is comparable to that observed within single extant species of therian mammals. Planarities of individual semicircular canals were the most variable measurements. Coiling of the cochlea and arc radii of the semicircular canals do not vary significantly in the specimens examined. The morphology of the bony labyrinth does not suggest any phylogenetic affinities of zhelestids, but the anatomy described will be useful for future studies of the evolution and physiology of the ear of mammals.

Published computed tomographic (CT) data from the holotype of the early tribosphenidan Slaughteria eruptens were reanalyzed to test a new hypothesis of dental formula in this taxon. Results indicate that Slaughteria had a premolar count of five, and that erupted (or erupting) teeth of the holotype all represent premolar loci—the p2, p3, dp4, and dp5 (a partially calcified p5 is identified below the dp5). This dental formula is supported by serial homology of cheek teeth between eutherians and metatherians and the pre-tribosphenic mammal Peramus. The presence of five premolars in Slaughters provides additional evidence that this tooth count is primitive for tribosphenidans as a whole. Slaughteria also presents an undocumented mode of tooth replacement, with a mixed alternating and sequential pattern. This pattern may represent the condition in other taxa with five premolars, such as Peramus and some early eutherians, with potential bearing on the polarity of tooth replacement at the base of the Tribosphenida.

Test-pit excavations from 1989 in Room 2 of Cathedral Cave yielded a diverse faunal assemblage, but age estimates derived from radioisotopic dates and bio chronological assessment were widely disparate. New excavations were undertaken in 2003 to increase faunal samples and clarify chronological resolution. Arvicoline rodents recovered from the 2003 excavation include Allophaiomys pliocaenicus, Microtus meadensis, M. paroperarius, Microtus sp., Mictomys meltoni or M. kansasensis, 4- and 5-triangle morphotypes of Lemmiscus curtatus, Ondatra zibethicus, and representatives of both ancient and recent lineages of Phenacomys. A maximum age for the fauna falls between 146.02 ± 2.584 and 153.7 ± 6.4 ka, as determined through uranium-series analyses of flowstones collected near the base of the excavation. Paleomagnetic analyses, and morphological data from recovered Ondatra, are consistent with that age interpretation. Cathedral Cave contains the youngest known Irvingtonian fauna, including the youngest records of Allophaiomys pliocaenicus, Microtus meadensis, and Microtus paroperarius. These records diminish the utility of those taxa for biochronologic refinement of fossil localities in western North America. Differences in biogeographic patterns of vertebrates in the Great Basin throughout the latest Pleistocene and Holocene are tied to topographic gradients and independent faunal histories. The Cathedral Cave biota provides a greater temporal depth for that dynamic, and provides important data demonstrating that higher-elevation fossil deposits yield diachronous biochronologic boundaries relative to lowland sites, and may require independent biochronologies. Recognition of the provincial nature of biochronologic boundaries is not new, but documented local-scale provincialism highlights conceptual challenges for broad-scale application of arvicoline biochronology in North America.

Canids were important members of Clarendonian faunas from the Great Plains and the southwestern part of North America, but they remain little studied in the northwestern portion of the continent. We present an overview of the canid fauna of Oregon's Juntura Formation, the best-preserved Clarendonian fauna from the northwest United States. The fauna is dominated by borophagines. The genus Carpocyon is reported for the first time in the Northwest and is represented from Juntura by postcrania. Most positively identifiable borophagine remains can be attributed to two species of Epicyon: E. saevus and E. haydeni. Only one specimen is attributable to the Caninae, showing that, as elsewhere, this subfamily remained a minor part of canid faunas until late in the Miocene. The presence of Epicyon and the absence of Aelurodon and Borophagus in the Juntura fauna provide support for the suggestion that these borophagine genera underwent a rapid ecological succession in the Northwest that constrains regional biostratigraphy.