The holotype specimen of the ischnacanthid acanthodian Atopacanthus dentatus comprises most of the posterior half of a dentigerous jaw bone, rather than a fragment from the middle of the jaw as was previously believed. A new diagnosis and revised description for the taxon are based on the holotype from the Rhinestreet Shale (Frasnian) and other specimens from the North Evans and Genundewa limestones (early Frasnian) of the Genesee Formation (late Givetian-early Frasnian); all of these dentigerous jaw bones were collected near Hamburg, New York state, U.S.A. An emended diagnosis for Atopacanthus clarifies the differences between it and other ischnacanthid genera.

Teeth, spines, and dermal denticles of chondrichthyans are reported from the Middle Pennsylvanian (Desmoinesian) Naco Formation of central Arizona. The most common elements are crushing teeth of the cochliodont Deltodus angularis, less common are teeth of D. sublaevis, Venustodus leidyi, Lagarodus angustus, “Cladodus” occidentalis, Petalodus ohioensis, Orodus sp., and Hybodontoidea. Fin spines of Acondylacanthus sp., Amelacanthus sp., and Physonemus sp., and the dermal denticle Petrodus patelliformis are also present. The material of Venustodus leidyi shows for the first time that this animal was heterodont, having arched anterior teeth with a v-shaped profile grading posteriorly into lower crescentic, and finally flattened teeth. Lagarodus angustus is shown to have at least three tooth morphotypes, and a new tooth arrangement is proposed in which small anterior teeth are replaced posteriorly by large crushing teeth arranged in whorls.

This fauna is similar to others in New Mexico, Colorado, and Ohio and constitutes a western extension of such faunas in North America. In addition, the presence of Deltodus sublaevis and Lagarodus angustus documents a range extension from a known European distribution, reinforcing the cosmopolitan nature of chondrichthyan faunas at this time.

A new genus and species belonging to the Macrosemiidae is described. This is the first record of a macrosemiid in the New World. The material was collected from the Early Cretaceous (Albian) Tlayúa Quarries, in Tepexi de Rodríguez, central México. The new taxon is a small, elongated fish that bears a combination of apomorphic and plesiomorphic characters including a divided dorsal fin with an area devoid of scales on either side, prearticular and coronoid bones with small pointed teeth, and strongly ornamented body scales. Phylogenetic analysis using PAUP revealed a close relationship of this new genus to Macrosemius and Legnonotus. The occurrence of macrosemiids in the Tlayúa beds indicates a wider distribution of the group within the Tethys Ocean, and represents the westernmost record of this group of neopterygians.

Diplospondichthys moreaui, gen. et. sp. nov. a freshwater fish from the Cenomanian of Morocco, is described. The fish is complete and articulated but only a few elements of the head are perfectly preserved. Therefore, the new taxon's relationships are essentially based on its very peculiar axial skeleton. Although we believe that the fish is probably a teleost, it displays such a strange combination of characters that we propose herein to classify it as an actinopterygian incertae sedis. The presence of pharyngeal teeth, diplospondylous and well-ossified vertebrae throughout the column, spine-bearing scutes on both sides of the body, and unpaired elements articulating with neural and haemal spines, are some of its unusual features. We believe that this fish could be of primary importance to understand the evolution of the axial skeleton in osteichthyans.

Early Oligocene deposits of the Jebel Qatrani Formation, Fayum Depression, Egypt, have provided three skulls that belong to a species of Lates (Perciformes, Latidae). This material differs from the other species of Lates in several features, such as the frontal bones of the fossils being broader anteriorly, the basioccipital facets having a more irregular shape, and the frontoparietal crests extending farther, and diverging, anteriorly. The Oligocene material therefore cannot be assigned to any of the described species of Lates, and is here described as a new species, L. qatraniensis. It is most similar to Lates niloticus, L. calcarifer, and L. angustifrons in the possession of an internal jugular bridge in the pterosphenoid, the parasphenoid contacting the pterosphenoid, and the anterior wall of the neurocranium (i.e., the anterior parts of the pterosphenoid, prootic, and ascending arm of the parasphenoid) extending significantly forward of the lateral commissure. Numerous cranial and postcranial elements that probably belong to the same new species are also described. This new species is the oldest Lates known from Africa.

Branchiosaurids are small Permo-Carboniferous temnospondyls that retained an immature morphology and external gills throughout ontogeny. Their preservation of numerous size classes makes them outstanding examples for the study of ontogenetic patterns. Here, ontogenetic data of several branchiosaurids are analyzed in order to reconstruct and compare developmental trajectories. These trajectories are based on numerical changes, marked by the successive appearance of bones in the skeleton. The earliest phases in the formation of the skull are preserved only in two species, Apateon caducus and Melanerpeton humbergense. Despite being distant relatives within the clade, their ontogenetic trajectories are similar in the early formation of dentigerous elements in the jaws and palate, and a slower development of the median skull roof as compared with the smaller branchiosaurids Apateon pedestris, A. gracilis, and A. dracyi. Patterns shared by all five species are (1) the late formation and slow completion of circumorbital elements and most details of their temporal succession, (2) an anteroposterior progression of ossification in the postcranium, and (3) a delayed appearance of the interclavicle with respect to outgroups. In addition, Melanerpeton humbergense and Apateon caducus share the earlier appearance of the humerus relative to the femur. Apart from differences in growth rates of single elements, the analyzed trajectories differ in the chronological order of bone formation. These discrepancies are largely restricted to the late phase of larval development, and they affect the formation of the hyobranchial apparatus, sclerotic ring, scapula, and the last dermal bones to appear in the skull roof (postfrontal, postorbital, tabular, and jugal). The observed variation is probably a result of disassociated heterochrony, which is supported by comparison with outgroups such as Sclerocephalus.

The temnospondyl amphibian Slaugenhopia texensis from the late Leonardian (Early Permian) San Angelo Formation of Knox County, north-central Texas, was described as a trimerorhachid by Olson. Restudy of the material shows it to be a member of the Tupilakosauridae and thus a more derived member of the clade Dvinosauria than the trimerorhachids. It possesses derived character-states of the Tupilakosauridae, including the reduced postfrontal, the postorbital-parietal suture, and the posterior pterygoid notch, but lacks the embolomerous centra of the Triassic tupilakosaurids. It is the earliest and most primitive tupilakosaurid and extends the history of the group back to the end of the Early Permian.

The cranial anatomy of plesiosaurs in the family Polycotylidae (Reptilia: Sauropterygia) has received renewed attention recently because various skull characters are thought to indicate plesiosauroid, rather than pliosauroid, affinities for this family. New data on the cranial anatomy of polycotylid plesiosaurs is presented, and is shown to compare closely to the structure of cryptocleidoid plesiosaurs. The morphology of known polycotylid taxa is reported and discussed, and a preliminary phylogenetic analysis is used to establish ingroup relationships of the Cryptocleidoidea. This study also presents new material referable to Polycotylus latipinnis from the Mooreville Chalk Formation of Alabama. This skeleton is largely complete, and although the skull is fragmentary it does preserve several regions not previously represented. The preserved portions demonstrate that the palate of Polycotylus is similar to that of Trinacromerum in the possession of robust epipterygoids, and similar to that of all other polycotylids in the possession of a large anterior interpterygoid vacuity. Polycotylus therefore displays the derived palate morphology common to all polycotylids, but also displays some plesiomorphic features. This impression is confirmed by the results of the cladistic analysis.

The discovery of a new genus and species of gavialoid at the Danian–Thanetian boundary, in the Oulad Abdoun Basin of Morocco, is consistent with an African origin of Gavialoidea. Argochampsa krebsi, n.g. n.sp., exhibits a particular shape of the anterior end of its premaxillae, transversely broad and strongly bent downwards, a shape found in distantly related taxa, such as pholidosaurids and Terminonaris. A phylogenetic analysis, suggests that A. krebsi is a primitive gavialoid, placed with Eogavialis africanum between ‘thoracosaurs’ (primitive Gavialoidea) and more derived taxa. This analysis supports the previous morphological analysis, which suggests a close relationship of Tomistominae with Crocodylinae, in contrast with the molecular analysis which give a closer relationships between Tomistoma and Gavialis. The marine nature of the layer where Argochampsa comes from is consistent with a marine origin for Argochampsa. This demonstrates the existence of marine adaptation in fossil species of primitive gavialoids, which may explain the dispersal of the fossil gavialoids to South America and Asia during and after the Oligocene.

Kerberosaurus manakini, gen. et sp. nov. (Dinosauria, Hadrosauridae) is described on the basis of disarticulated skull elements from the Maastrichtian Tsagayan Formation of Blagoveschensk, Far Eastern Russia. This flat-headed hadrosaur is characterized by a unique morphology of the lateral wall of the braincase, a particularly narrow frontal, a depressed rostral margin of the parietal, a strong, wide and flattened crest around the circumnarial depression, and a very prominent hook-like palatine process on the maxilla. A phylogenetic analysis, based on 21 cranial characters, indicates that, among hadrosaurines, Kerberosaurus is the sister taxon of a monophyletic group formed by Prosaurolophus and Saurolophus. Several independent hadrosaurid lineages migrated from western North America to eastern Asia, probably by late Campanian to early Maastrichtian time. At the end of the Maastrichtian, completely different dinosaur faunas developed in both regions, indicating some kind of geographical or paleoecological barrier.

In recent years, mousebirds (Aves, Coliiformes) have been recognized as one of the predominant groups of small perching birds in the early Tertiary of the Northern Hemisphere. Two major lineages can be distinguished, the Sandcoleidae, which are exclusively known from Paleocene and Eocene deposits, and the Coliidae, which have been found in Upper Eocene to Pliocene deposits and also include the six extant African species. Here we describe a nearly complete tarsometatarsus of a mousebird from the middle Eocene to upper Oligocene fissure fillings of the Quercy in France. The specimen is tentatively referred to Selmes absurdipes Peters, 1999, and represents a previously unknown tarsometatarsal morphology that combines derived characters of Sandcoleidae and Coliidae. It provides further evidence that Selmes is a stem lineage representative of the Coliidae and not a sandcoleid bird as assumed in the original description. Classification of Selmes into the Coliidae is also supported by a cladistic analysis of 19 morphological characters.

The Upper Cretaceous marine squamate Pontosaurus lesinensis is redescribed. Extensive re-preparation has exposed new details of the skull, mandibles, and postcranial skeleton. Important new characteristics include a unique supraoccipital-parietal articulation, elongation of all postdentary bones, at least twelve cervical vertebrae, hypapophyses with large unfused peduncles, twenty-eight dorsal vertebrae, and a fused scapulocoracoid with a primary coracoid emargination. Cladistic analysis of all anguimorph squamates, including mosasaurs, aigialosaurs, dolichosaurs, snakes, and Pontosaurus, resulted in 3-most parsimonious trees: 334 steps; C.I. 0.78; H.I. 0.42; R.I. 0.81. Both the strict consensus tree and the 50% majority-rule consensus tree found support for the monophyly of the Pythonomorpha, containing mosasaurs, aigialosaurs, dolichosaurs, and snakes (pachyophiids and modern snakes). Pontosaurus is found to be a dolichosaur nested within the clade Pythonomorpha as the sister taxon to Adriosaurus and the Ophidia.

Two new specimens of the aquatic sloth Thalassocnus from the Pliocene of Peru are described, one of T. carolomartini McDonald and Muizon, 2002 and the other T. yaucensis, sp. nov. Comparisons with the type species of Thalassocnus, T. natans, demonstrates that T. carolomartini and T. yaucensis are more similar morphologically to each other than to other species of the genus and are more derived. For example, both have a more elongated rostrum (premaxillae and mandibular spout) and more robust, quadrate to circular molariform teeth. The aquatic sloth Thalassocnus is sufficiently distinct morphologically that it is placed in a new subfamily, the Thalassocninae, and the Nothrotheriinae is raised to family rank. The morphological features shared by T. carolomartini and T. yaucensis indicate these species were better adapted to grazing on marine vegetation than earlier species of Thalassocnus.

The aquatic sloth Thalassocnus is represented by five species that lived along the coast of Peru from the late Miocene through the late Pliocene. A detailed comparison of the cranial and mandibular anatomy of these species indicates different feeding adaptations. The three older species of Thalassocnus (T. antiquus, T. natans, and T. littoralis) were probably partial grazers (intermediate or mixed feeders) and the transverse component of mandibular movement was very minor, if any. They were probably feeding partially on stranded sea weeds or sea grasses, or in very shallow waters (less than 1 m) as indicated by the abundant dental striae of their molariform teeth created by ingestion of sand. The two younger species (T. carolomartini and T. yaucensis) were more specialized grazers than the three older species and had a distinct transverse component in their mandibular movement. Their teeth almost totally lack dental striae. These two species were probably feeding exclusively in the water at a greater depth than the older species.

A single layer of radial enamel in the incisors represents the plesiomorphic condition for stem-lineage representatives of Glires (Lagomorpha and Rodentia). A single layer of radial enamel is detected in the incisors of the zalambdalestid Barunlestes butleri and the pseudictopid Pseudictops lophiodon as well as the eurymylid Eurymylus laticeps. The eurymylid Matutinia nitidulus exhibits a more derived, double-layered schmelzmuster with Hunter-Schreger bands (HSB) in the portio interna (PI) and radial enamel in the portio externa (PE). Mimotonids are characterized by a schmelzmuster with HSB: Anatolimys rozhdestvenskii has double-layered enamel (PI with HSB, PE with radial enamel) and two undetermined mimotonids from Mongolia exhibit a single-layered enamel. An incisor of an undetermined leporid (Strenulagus or Aktashmys) from the early Eocene of Kyrgyzstan, one of the geologically oldest studied, has double-layered schmelzmuster with HSB in the PI and radial enamel in the PE, whereas all other leporids have single-layered enamel with HSB. This is evidence that the single-layered leporid incisor schmelzmuster is derived from a double-layered condition. The presence of multilayered schmelzmuster in upper and lower incisors of Ochotonidae with modified radial enamel, HSB, and tangential enamel is corroborated. All three species of the supposed ochotonid Desmatolagus (D. gobiensis, D. robustus, and D. vetustus) exhibit a single-layered schmelzmuster with HSB and therefore are transferred to the Leporidae. Ochotonid schmelzmuster was derived by a different pathway than leporid schmelzmuster and possibly originated from that of yet poorly known early Paleogene Gliriformes such as Decipomys mongoliensis. This indicates that the ochotonid-leporid divergence is much older than previously believed.

The probable diets of members of the extinct ruminant family Dromomerycidae were determined via an assessment of gross anatomical correlates of feeding strategy, mesowear analysis, and microscopic scar topography of enamel surfaces of cheek teeth. Discriminant models derived from 108 extant ruminants of known diet were applied to fossil taxa to ascertain probable trophic habits in dromomerycids. Microwear and mesowear analyses of molar tooth wear supplemented this gross skull and tooth morphological assessment as a means of providing more direct and independent sources of evidence for the nature and potential shifts in diet within dromomerycid lineages. In general, estimations of diets obtained from the study of gross morphology correlated well with those obtained from wear patterns. However, this was not always the case, suggesting that independent means of dietary analysis are critical when attempting to reconstruct paleodiets. In addition, hypsodonty (relative molar crown height) proved to be problematic as a variable in determining the diet of these extinct taxa. Information obtained from gross morphology, microwear, and mesowear support the hypothesis that later species of the Dromomerycidae within the tribe Cranioceratini had a shift in diet toward coarser food materials as a response to a trend toward increasing aridity and a shift in vegetational structure in the late Miocene–early Pliocene of North America.

Aelurodon montanensis, sp. nov. (Carnivora, Canidae, Borophaginae), is described from a new locality, Aelurodon Cut, near Pipestone Springs in Jefferson County, Montana. The new species is a primitive representative of the previously recognized Aelurodon mcgrewi–A. stirtoni clade, one of the most hypercarnivorous, relatively rare clades in the subfamily Borophaginae. It shares with this clade such derived characters as a broadened posterior cingulum of p3, initial development of a posteriorly expanded M1 internal cingulum, and similarities in dental proportions. Evolutionary trends within this clade include reduction in size, increasingly hypercarnivorous dentition with lengthened shearing blades on the upper and lower carnassials, a more trenchant talonid on m1, a reduced grinding part of upper and lower molars, and a posteriorly expanded M1 internal cingulum. Based on the stage of evolution of the new canid and on an associated metapodial fragment of Aepycamelus, we tentatively assign an early Barstovian age to the Aelurodon Cut locality.

Eobalaenoptera harrisoni, gen. et sp. nov., is described from a partial skeleton collected from the middle Miocene Calvert Formation of Virginia. Characteristics of this taxon, particularly of the petrosal, indicate that the new whale is a member of the clade that includes the Balaenopteridae (rorquals) and Eschrichtidae (gray whales) to the exclusion of “cetotheres” and the Balaenidae (right whales). Some of the probable synapomorphies of this clade include an elongate pars cochlearis, a tubular internal auditory meatus, the greater petrosal nerve foramen on the tympanic side of the petrosal, the stylomastoid fossa extending onto the posterior process of the petrosal, no medial groove on the pars cochlearis, four digits on each forelimb, depressed supraorbital processes, and ascending processes of maxillae extending onto the vertex. The approximate 14-million-year age of the specimen makes it the oldest known member of the clade by some 3 to 5 million years, and extends the fossil record of this clade closer to the divergence time estimated by some recent molecular studies.

A new species of hippopotamid, Hexaprotodon bruneti, sp. nov., was discovered in both the Hata Member of the Bouri Formation and at upper Maka in the Middle Awash study area of Ethiopia. Hexaprotodon bruneti is characterized by an enlarged i3 and differs from all African fossil and living hippos in the shape of its mandibular symphysis. It has stronger phylogenetic affinities with Pliocene hippopotamids of southern Asia than with African species. This probable Asian origin agrees with a hypothesis of an important faunal turnover in Africa about 2.5 Ma, perhaps linked with climatic change.

A new species of Notochoerus, N. clarki, sp. nov., has been identified from three Pliocene Formations in Ethiopia, the Omo Shungura, Konso, and Bouri (Middle Awash). This taxon, formerly known from isolated dentognathic elements and attributed to a long-lasting Notochoerus euilus, represents the fourth species of Notochoerus to be recognized. Its temporal distribution shows that Notochoerus euilus was not the long-lasting species formerly imagined. The new species' anatomical specializations, unusual spatial distribution, and apparent sympatry with its close relative Notochoerus scotti all imply narrow niche partitioning in eastern African suids during the Pliocene.

The common pyrothere of Salla, Bolivia (Deseadan, late Oligocene) is described as a new species, Pyrotherium macfaddeni. It is distinguished by its small size (linear dimensions but two-thirds those of Pyrotherium romeroi) and pi-shaped upper premolars. Recovery at Salla of the first known calcaneum of Pyrotherium permits the description and analysis of the proximal tarsus. It is distinctive by the pronounced dorsoventral compression of the calcaneal tuber and similar flattening of the astragalar trochlea, concavity of the ectal facet of the calcaneum, and extreme reduction of contact between the calcaneum and the cuboid. These derived characters were not seen in any other mammal examined except the embrithopod Arsinoitherium from the Tertiary of Africa. Whether this is due to common ancestry or the unusual mode of locomotion used by these animals (graviportal and plantigrade) remains to be seen. This more complete study of the tarsus of Pyrotherium fails to support the proposed relationship of pyrotheres with the Xenungulata.