Morphological studies of fossil and extant shark teeth have typically been qualitative in nature, with resulting taxonomic problems due to the complicated forms of heterodonty exhibited by many sharks. This is apparent in the designation of fossil species assigned to Isurus (Lamniformes), where the status of the putative Neogene fossil species Isurus xiphodon and I. hastalis is solely based upon supposed differences in tooth morphology. Here we apply the geometric morphometric techniques of Procrustes superimposition, resampling-based Goodall's F-test, and canonical variates analysis to extant Isurus teeth, with the goal of assessing whether these quantitative analytical techniques provide a more objective basis for taxonomic decisions than do traditional qualitative morphological descriptions. These quantitative techniques are then applied to I. hastalis and I. xiphodon to examine whether I. xiphodon should be considered a junior synonym of I. hastalis or a separate species. Results show that geometric morphometric techniques can differentiate between the two extant species as well as the two extinct species, supporting I. xiphodon as a valid taxon. We suggest that this type of analysis is applicable for examining tooth-based species delimitations of sharks with both extant and extinct members, and has the potential to be applied to other fossil shark species as well.

Shark teeth are the most common vertebrate fossils found along the western shore of Chesapeake Bay at Calvert Cliffs in Maryland. The stratigraphic distribution of teeth within the cliffs has not yet been documented. We utilized museum collections of in situ teeth to access their distribution within stratigraphic beds and a large selection of float teeth retrieved from Calvert County beaches as a proxy for the distribution of teeth within stratigraphic beds and across underlying beaches. Museum collections provide 1,866 teeth recorded in situ; float collections yield a total of 24,409 teeth. These data sets offer different, but complementary, results.

Miocene sediments along Calvert Cliffs comprise the Calvert, Choptank, and St. Marys formations. Over 96% of all teeth in the in situ data set derive from the Calvert Formation, likely due to favorable paleoenvironmental conditions for sharks. The non-uniform stratigraphic distribution of teeth is further supported by an uneven distribution of teeth collected on beaches below the cliffs. Samples from northern localities contained more float specimens; cliffs in this area are composed almost entirely of the Calvert Formation.

Fifteen genera are represented in the in situ and float collections. The main constituents are Carcharhinus spp., Hemipristis serra, Galeocerdo spp., Isurus spp., and Carcharias spp. Most of these genera exhibit significant unidirectional trends in the proportional abundance of teeth across Calvert Cliffs beaches. Factors influencing these variations remain unclear, but the overall dominance of carcharhiniforms over lamniform and other sharks observed for the Miocene persists in modern nearshore environments.

The earliest Actinoptergyii (ray-finned fishes) and Sarcopterygii (lobe-finned fishes) have been studied intensely, and a consistent picture of interrelationships has begun to emerge for the latter. In contrast, there has been minimal documentation of the pattern of character acquisition leading to the osteichthyan crown. We review the synapomorphies proposed for various levels within osteichthyan phylogeny (total group; Acanthodes crown group; crown group; Sarcoptergyii; Actinopterygii), confirming some, rejecting others, and making new additions. This distribution of characters is used to interpret the placement of problematic Siluro-Devonian genera traditionally assigned to Actinopterygii, and suggests these taxa are stem osteichthyans. Earlier placements of these forms within the crown are symptomatic of taxonomies based on unpolarized similarities rather than synapomorphies.

A new double-armored member of the Ellimmichthyiformes (Clupeomorpha, Teleostei) is described from the Cenomanian (Upper Cretaceous) of Ein Yabrud, near Ramallah, Middle East. The anatomical description of Rhombichthys intoccabilis, gen. et sp. nov., is based on 13 subcomplete or incomplete acid-prepared specimens. This taxon shows several remarkable characters such as an important dorsoventral elongation of the lateral wings of the ventral scutes that give an apex-shaped ventral profile in the biggest specimens. Some dorsal fin rays are very extended and branched, and the dorsal fin extends along the major part of the dorsal margin of the body. Rhombichthys intoccabilis, gen. et sp. nov., shares the synapormorphies of the family Paraclupeidae and the subfamily Paraclupeinae. It appears closely related to the genera Triplomystus and Ezkutuberezi, mainly in the basis of the shape of dorsal and ventral scutes and the absence of a hypural diastema.

The tetrapodomorph fish Marsdenichthys longioccipitus from the Givetian-Frasnian of Mt. Howitt, Victoria, Australia, occupies an uncertain phylogenetic position. Marsdenichthys has been linked to the base of the Tristichopteridae, as well as to the poorly known Northern Hemisphere form Rhizodopsis, based on the presence of rounded scales bearing a median boss on the internal surface. However, its affinities to these taxa are ambiguous, due to the incomplete preservation of the two Marsdenichthys specimens initially described. For the first time, we present significant information regarding the cheek and palate of Marsdenichthys, based on the descriptions of two new specimens from Mt. Howitt. New autapomorphies for Marsdenichthys are proposed, including the presence of a bar-like maxilla being approximately equal in depth to the dentary, and a rectangular anterior termination of the lacrimal. Several plesiomorphic features are described from the palate, including rounded vomer morphology lacking a posterior process, a relatively short, broad parasphenoid, and a dermopalatine approximately equal in length to the ectopterygoid. No synapomorphies are shared between Marsdenichthys and tristichopterids. Scale morphology is redescribed, and shown to exhibit concentric rings on the external surface, as in Rhizodopsis. However, differences in skull morphology, such as the lack of an external opening for the pineal foramen in Rhizodopsis, suggest that this scale morphology may have evolved independently.

The osteohistology including bone cross-sectional geometry of skeletal elements such as the limb bones, ribs, and intercentra of three Triassic temnospondyl taxa from India were examined to reveal varied bone microstructure and differing growth patterns. The Early Triassic trematosaurid examined is characterized by a change in tissue type from a well-vascularized fibrolamellar bone early in ontogeny to peripheral lamellar bone and lines of arrested growth later in ontogeny, suggesting a fast initial growth followed by a slow and intermittent growth later in life. In contrast, the Middle Triassic paracyclotosaurid and the Late Triassic chigutisaurid examined had a cyclical, overall slow growth, as evidenced from predominance of lamellar bone in the cortex. It is hypothesized that the rapid growth of the trematosaurids was an attempt to stabilize the ecosystem after the Permo-Triassic extinction event. Fibrolamellar bone tissue is described for the first time in a Triassic temnospondyl. Bone cross-sectional geometry, low-to-average cortical porosity, and other parameters imply that the members of the Early and Middle Triassic taxa recovered from India retained a high level of terrestriality. The high cortical porosity and extensive medullary spongiosa suggest that the Late Triassic chigutisaurids had a semi-aquatic or aquatic life style. The varying cortical thickness of the limb bones in paracyclotosaurids may be attributed to different biomechanical constraints.

Redescription of the Upper Cretaceous marine squamate Acteosaurus tommasinii von Meyer, 1860, notes at least 10 cervical vertebrae, 27 dorsal vertebrae, an absence of pachyostosis on the vertebrae and ribs, overall limb reduction where the forelimbs are smaller than the hind limbs, a flattened pubic bone with a square pubic process and subrectangular descending ramus, small postzygapophyses on the trunk vertebrae, long and narrow neural spines on the caudal vertebrae, and posteroventrally positioned, unfused haemal arches on the caudals. Cladistic analysis of Acteosaurus and other marine squamates, including mosasauroids, dolichosaurs, pontosaurs, Adriosaurus, and Aphanizocnemus, and living and fossil snakes (Dinilysia, Yurlunggur, Eupodophis, Haasiophis, Pachyrhachis, Scolecophidia, Macrostomata, and Anilioidea) resulted in three most-parsimonious trees of 280 steps (C.I. = 0.59, R.I. = 0.81, R.C. = 0.48). All recovered tree topologies found support for the monophyly of the clade Ophidiomorpha, inclusive of Dolichosauridae (Dolichosaurus, Coniasaurus), Pontosaurus, Aphanizocnemus, Adriosaurus, Acteosaurus, and Ophidia. Acteosaurus is found to be a basal ophidiomorph and the sister taxon to the Ophidia.

A Late Cretaceous (Maastrichtian) assemblage of snakes from the Maevarano Formation of the Mahajanga Basin, northwestern Madagascar, constitutes the only fossil record of snakes from the island. The assemblage, which lived in a highly seasonal, semi-arid climate, includes only archaic forms belonging to the Madtsoiidae and Nigerophiidae, and therefore no representatives of extant Malagasy clades. A large sample of exquisitely preserved vertebrae and several ribs are assigned to Madtsoia madagascariensis, a long (almost 8 m), heavy-bodied ambush predator inferred to have subdued its prey via constriction. A new madtsoiid genus and species, Menarana nosymena, is represented by several associated vertebrae and rib fragments, and part of the basicranium. It was approximately 2.4 m long and appears to have been a powerful, head-first burrower, or at least to have had a burrowing ancestry. Kelyophis hechti, by far the smallest snake in the assemblage (<1 m long), is a new genus and species of primitive nigerophiid based on six isolated vertebral specimens. It was not as specialized for the aquatic lifestyle inferred for other nigerophiids. Although recent molecular phylogeographic studies suggest an early colonization of Madagascar by snakes ancestral to modern Malagasy boids, with subsequent vicariant evolution, the Maevarano Formation assemblage offers no support for this hypothesis. The repeated pattern of extinct archaic lineages being replaced on Madagascar by basal stocks of extant clades (e.g., Anura, Crocodyliformes, Avialae, Mammalia) after the Late Cretaceous is also a plausible scenario for the origin of the extant Malagasy snake fauna.

The fossil record of dyrosaurid crocodyliforms spans the Late Cretaceous to Middle Eocene of Africa, Asia, Europe, North America, and South America. Prior to this study, specimens from South America have been limited to a few fossils with only two taxa diagnosed. We describe a nearly complete skull and unassociated mandible of a new dyrosaurid, Cerrejonisuchus improcerus gen. et sp. nov., from the Paleocene Cerrejón Formation of northeastern Colombia. The skull of C. improcerus has relatively elongate supratemporal fenestrae and well-developed occipital tuberosities, both diagnostic characteristics of Dyrosauridae. The rostrum of adult C. improcerus comprises 54–59% of the length of the skull, making it the shortest snout of any known dyrosaurid. A cladistic analysis using 82 cranial and mandibular characters for all species of Dyrosauridae known from crania yielded two most-parsimonious cladograms with C. improcerus as the sister taxon to a clade including Arambourgisuchus, Dyrosaurus, Hyposaurus, Congosaurus, Rhabdognathus, Atlantosuchus, and Guarinisuchus. Only Chenanisuchus, Sokotosuchus, and Phosphatosaurus, all known only from Africa, are more primitive within Dyrosauridae. Chenanisuchus from the Paleocene of Morocco, the only other known short-snouted dyrosaurid, is not closely related to C. improcerus and a short-snouted condition appears to have evolved independently at least twice within Dyrosauridae. Our analysis supports an African origin of Dyrosauridae with dispersals to the New World by the Late Cretaceous or earliest Paleocene. The presence of C. improcerus, together with undescribed taxa from the Cerrejón Formation, suggests a radiation of dyrosaurid crocodyliforms, possibly following the K-P boundary, in tropical South America.

A new rhamphorhynchid pterosaur species, Sericipterus wucaiwanensis, gen. et sp. nov., is described from the Upper Jurassic part of the Shishugou Formation in the Xinjiang Autonomous Region of northwest China. Pterosaurs from this unit are the earliest and only records of pterosaurs in the Jurassic of northwest China. The individual specimen is one of the largest known among ‘rhamphorhynchoids,’ or non-pterodactyloid pterosaurs. The holotype comprises an associated skeleton of mostly disarticulated, largely three-dimensional material. Although partly crushed, the preservation in this specimen reveals morphology rarely seen in non-pterodactyloid pterosaurs. This includes a distinct cervical intervertebral articulation morphology that is proposed to be widespread among the non-pterodactyloids. The skull of this new specimen is most similar to that of other rhamphorhynchids, Angustinaripterus longicephalus and Harpactognathus gentryii, found in terrestrial deposits. A phylogenetic analysis of 18 non-pterodactyloid pterosaurs and the Pterodactyloidea places Sericipterus wucaiwanensis with these species within the Rhamphorhynchinae and a monophyletic Rhamphorhynchidae. Unlike previous phylogenetic analyses, the Dimorphodontidae is paraphyletic, the Campylognathoididae is polyphyletic, and the Anurognathidae is the sister group of the Pterodactyloidea. Sericipterus wucaiwanensis, Angustinaripterus longicephalus, Harpactognathus gentryii represent a clade of large pterosaurs that likely lived in the terrestrial settings in which they preserved.

Three clutches and eight additional eggs are described from the Upper Cretaceous Chichengshan Formation in the Lishui Basin of Zhejiang Province, China. The three clutches contain 6–18 partial or complete spherical eggs, 14–18 cm in diameter. The eggshell thickness and reticulate pore system are identical to Dictyoolithus hongpoensis Zhao, 1994. However, the eggshell lacks superimposed shell units previously reported in this oospecies. The difference in microstructure most likely results from the reliance on thin section analysis in the original study; furthermore, superimposed shell units are inadequately documented in all Dictyoolithus oospecies due to the absence of scanning electron microscopy (SEM) or low (×45) magnification of SEM imaging. Cladistic analysis and the presence of the following characters support a theropod affinity of Dictyoolithus hongpoensis: relatively narrow spacing of nucleation sites, mammillary cones with blocky calcite cleavage, prismatic columns, and parallel laminae within the shell units. We reevaluate previous assignment of Dictyoolithus eggs to the Dinosauroid-spherulitic Basic Type and advocate discontinuation of Basic Type and Morphotype in fossil egg classification.

The Quantou Formation of Jilin Province, People's Republic of China, has recently yielded an important new fauna of ‘middle’ Cretaceous vertebrates. This fauna includes the small-bodied cerapodan ornithischian dinosaur Changchunsaurus parvus, represented by excellent cranial and postcranial material. When initially described, Changchunsaurus was hypothesed to represent one of the most basal known ornithopods; however, similarities to ceratopsians were also noted, suggesting that Changchunsaurus may be crucial to elucidating the interrelationships of basal cerapodans, one of most problematic areas of ornithischian phylogeny. Here we present a detailed description of the craniodental anatomy of Changchunsaurus, rediagnose the taxon based upon three autapomorphies, and provide comparisons to other basal cerapodans, as a foundation for future studies of basal cerapodan relationships. Changchunsaurus shows strong similarities to the Chinese Early Cretaceous cerapodan Jeholosaurus, and it is likely that they are sister taxa.

The Eocene Green River Formation provides one of the richest records of fossil birds worldwide. As part of a reevaluation of this avifauna, we describe 12 new specimens of the stem roller Primobucco mcgrewi from the well-dated (51.66 ± 0.09 Ma) Fossil Butte Member (FBM) of the Green River Formation of Wyoming. FBM specimens represent most of avian diversity in the Green River Formation and include the oldest well-constrained record of the roller lineage (Coracii). These fossils provide new anatomical data, including the first observations on the palate, and broaden our understanding of the distribution, abundance, and taphonomy of P. mcgrewi. Using museum records and lithological comparisons, 14 of the 15 known P. mcgrewi specimens can now be assigned to specific quarries within Fossil Lake. The species is now known from five distinct localities representing both nearshore and mid-lake environments and accounts for >10% of the 148 FBM avian specimens reviewed in this study. Pectoral elements are disproportionately represented in the FBM P. mcgrewi specimens, and more than half of the sample exhibits broken elements. These new fossils and other key specimens from the Eocene of North America and Europe clarify our understanding of the evolution of the clade Coracii. Extant parts of this lineage (i.e., Coraciidae and Brachypteraciidae) have specialized ecologies and restricted Old World distributions, whereas stem representatives appear more generalized and were a major component of some North American avifaunas.

Four species of rodents (two heteromyids and two cricetids) and one lagomorph are identified from the late Tertiary Sevier River Formation of Utah. The heteromyids include a new genus and species of heteromyine, Metaliomys sevierensis, which is intermediate in morphology between the Clarendonian and early Hemphillian Diprionomys Kellogg and the extant genera Liomys and Heteromys. A single specimen is referred to Diprionomys sp., cf. D. minimus (Kellogg). The cricetid Paronychomys lemredfieldi Jacobs is known from the Hemphillian of Arizona. The second cricetid is referred to a new genus Basirepomys. Peromyscus pliocenicus Wilson from the Hemphillian of California is designated as the type species of the new genus, to which the new species B. robertsi from Utah is referred. Basirepomys is viewed as intermediate between Peromyscus and the basal neotomyine Repomys May from the late Hemphillian and Blancan. The only lagomorph in the fauna is Hypolagus vetus (Kellogg). Four of the taxa recognized from the Sevier River Formation (Diprionomys, Paronychomys lemredfieldi, Basirepomys, and Hypolagus vetus) are elsewhere known from the Hemphillian of North America. However, it is not possible at this time to determine whether the fauna is early or late Hemphillian.

Most recent phylogenetic analyses place the Cainotheriidae within the Tylopoda, but doubts about this placement within Tylopoda have been persistent. The Cainotheriidae are well known from numerous specimens and their cranial anatomy is well documented from complete, partial and disarticulated cranial material. However, high-resolution computed tomographic (CT) scans can still provide additional data to resolve problems in the interpretation of the auditory region, and allow comparison with other tylopod and ruminant taxa. Cainotheriids share several features with various groups within the Tylopoda, including an enlarged mastoid fossa, an inflated auditory bulla filled with cancellous bone, the presence of a sinus venosus temporalis, and what has been interpreted as a large flange of the periotic enclosing the petrobasilar canal. The reconstruction of the petrobasilar canal has been difficult to interpret, as the published figures are unclear. A micro-CT scan of Cainotherium (YPM 25037) shows the morphology is more complex. The periotic shows a smaller flange that does not enclose the petrobasilar canal. The skull base shows different arrangement of bones from other artiodactyls, presumably as a result of the enlargement of the auditory bulla, which has also affected the course of the petrobasilar canal. The otic region of Cainotherium shows no resemblances to ruminants, and features of this region are consistent with the Cainotheriidae being either a sister taxon to Tylopoda Ruminantia, or with inclusion in a tylopod grouping.

The family Nimravidae is a group of cat-like carnivorans that evolved sabertooth forms in parallel to Felidae. The last records of nimravids are represented by species of the North American genus Barbourofelis. Fossils of Barbourofelis found in Clarendonian North American Land Mammal Age (NALMA) deposits of California represent the western-most occurrences of the genus. Here we describe new material of Barbourofelis whitfordi from the late Miocene Dove Spring Formation (12.5–8 Ma) of the northwestern Mojave Desert, southern California, including the first known saber and confirmed upper cheek dentition of the species. Consistent with the delayed canine eruption observed in other Barbourofelis species, the newly discovered permanent cheek teeth are associated with deciduous upper canines. The upper and lower third premolars of B. whitfordi are larger in size relative to the carnassials, and less reduced in cusp morphology than other Barbourofelis species. In this regard, p3 morphology and size in B. whitfordi resemble that of the Eurasian Sansanosmilus more so than its congeneric species. The known stratigraphic range of B. whitfordi within the Dove Spring Formation spans a two-million-year period from 10.5 to 8.4 Ma. Based on a distal humerus described in this study, the record of Barbourofelis in the Dove Spring Formation now extends to the Cl1–Cl2 boundary at ∼12 Ma. A comparison of known Barbourofelis in the United States revealed that the B. morrisi—B. loveorum—B. fricki sequence might represent a single anagenetic lineage, whereas B. whitfordi represents a side lineage contemporaneous with B. morrisi during much of the Clarendonian NALMA.

The carnivores preserved in the late Pleistocene Rancho La Brea tar seep deposits display a remarkably high incidence of teeth broken in life as compared with modern species. In a previous study examining tooth breakage, tooth wear and individual age of Canis dirus over different periods in time, we found that Pit 13 C. dirus (about 15,000 years before present [ybp]) exhibited heavier tooth wear and fractured their teeth about three times more often than those of the younger Pit 61/67 (about 12,000 ybp). No significant difference was found in the age structure of the population, suggesting this came from differences in feeding behavior, likely bone consumption, at these two times. In this study, we extend this work to the Rancho La Brea sabertooth cat, Smilodon fatalis, a hypercamivore with more specialized teeth and feeding behavior. We looked at tooth breakage, tooth wear, and individual age of S. fatalis compared with C. dirus from similar time intervals. As in the previous study, the age structure of the Smilodon samples did not differ between different time intervals. Interestingly, S. fatalis had consistent and higher levels of tooth breakage and apparent average age than C. dirus in either location, and tooth wear was similar to that observed in the more worn Pit 13 sample of C. dirus. This may demonstrate that S. fatalis was consuming more bone, and/or that S. fatalis individuals were older, had different relative dentine deposition rates, or might reflect the greater vulnerability of the sabercats' narrow teeth to wear and fracture.

In this study, we review the previous evidence on the paleobiology of the giant, ‘short-faced’ bear Arctodus simus (Mammalia: Carnivora: Ursidae) and contribute new ecomorphological inferences on the paleobiology of this enigmatic species. Craniodental variables are used in a comparative morphometric study across the families Felidae, Hyaenidae, Canidae, and Ursidae. Principal components analyses (PCAs) do not show an ecomorphological adaptation towards bonecracking or hypercarnivory in the ‘short-faced’ bear. In contrast, PCAs and discriminant analyses restricted to the craniodental data set of ursids suggest close morphological resemblance between A. simus and the extant omnivorous bears. In addition, the scaling of snout length on neurocranial length in bears indicates that the face of A. simus was not particularly short. Body mass estimates obtained from major limb bone measurements reveal that A. simus specimens of around 1000 kilograms were more common than previously suspected. Scaling relationships in extant bears of limb lengths on the least width of the femoral shaft (the variable best correlated with body mass) indicate that A. simus was not as relatively long-legged as previously thought. For these reasons, although the isotopic signature of A. simus has been interpreted as evidencing that it consumed large amounts of flesh relative to some contemporary populations of Ursus arctos, our results do not support the previous views of A. simus as a fast-running super-predator or as a specialized scavenger. In contrast, the picture that emerges from this study is one of a colossal omnivorous bear whose diet probably varied according to resource availability.