The dicynodont wastebasket genus Dicynodon is revised following a comprehensive review of nominal species. Most nominal species of Dicynodon pertain to other well-known dicynodont genera, especially Oudenodon and Diictodon. Of the Karoo Permian species that are referable to “Dicynodon” sensu lato, we recognize four common, valid morphospecies: Dicynodon lacerticeps, D. leoniceps, D. woodwardi, and Dinanomodon gilli, comb. nov. Eleven additional species of “Dicynodon” are recognized worldwide: D. alticeps, D. amalitzkii, D. bathyrhynchus, D. benjamini, D. bogdaensis, D. huenei, D. limbus, D. sinkianensis, D. traquairi, D. trautscholdi, and D. vanhoepeni. Morphometric analysis of D. lacerticeps and D. leoniceps specimens recovers statistically significant separation between these species in snout profile and squamosal shape, supporting their distinction. A new phylogenetic analysis of Anomodontia reveals that “Dicynodon” is polyphyletic, necessitating taxonomic revision at the generic level. D. benjamini and D. limbus are basal cryptodonts, whereas the other valid “Dicynodon” species are basal dicynodontoids. The genus Dicynodon is restricted to D. lacerticeps and D. huenei. We reinstate use of Daptocephalus, Sintocephalus, Turfanodon, Daqingshanodon, Jimusaria, and Gordonia for other species. We synonymize Vivaxosaurus permirus and Dicynodon trautscholdi (as V. trautscholdi, comb, nov.) We establish new generic names for several species formerly included in Dicynodon: Peramodon amalitzkii, comb, nov., Keyseria benjamini, comb, nov., Euptychognathus bathyrhynchus, comb, nov., Syops vanhoepeni, comb, nov., and Basilodon woodwardi, comb. nov. Of the main Karoo Permian taxa, Dicynodon, Basilodon, and Dinanomodon range throughout the Cistecephalus and Dicynodon assemblage zones, but Daptocephalus is restricted to the Dicynodon Assemblage Zone.

A new protocetid archaeocete, Aegyptocetus tarfa, is represented by a nearly complete cranium and an associated partial skeleton. The specimen was recovered when marbleized limestone was imported commercially to Italy and cut into decorative facing stone. It came from middle Eocene Tethyan marine strata of the Gebel Hof Formation of Wadi Tarfa in the Eastern Desert of Egypt. Exceptional preservation and preparation enables study of some internal features of the skull as well as its external morphology. The skull of Aegyptocetus is unusual in having the rostrum and frontal portions of the cranium deflected more ventrally relative to the braincase than is typical for archaeocetes. This ventral deflection, clinorhynchy, is a rare specialization related to feeding or hearing that is widely distributed across mammals. Aegyptocetus has well-developed ethmoidal turbinai bones, indicating retention of a functional sense of smell. It also has cranial asymmetry, thinning of the lateral walls of the dentaries, enlarged mandibular canals, and thinning of the anterolateral walls of the tympanic bullae, indicating enhanced ability to hear in water. Neural spines are long on thoracic vertebrae Tl through T8, suggesting that Aegyptocetus was able to support its weight on land like other protocetids. This combination of terrestrial and aquatic characteristics is consistent with interpretation of protocetids as semiaquatic. The pattern of tooth marks preserved on the ribs of Aegyptocetus indicates that the individual studied here was attacked by a large shark, but it is not certain whether this was the cause of death.

Although teeth are considered one of the most important steps in vertebrate evolution, details of their origins are obscure. Two prominent and opposing theories for the evolution of the vertebrate dentition are current: the ‘Outside-in’ hypothesis and the ‘inside-out’ hypothesis. One of the main arguments against the ‘outside-in’ hypothesis is that, although similarities between teeth and scales have been observed, there is little fossil evidence of transitional forms between the two structures. Specimens of ischnacanthid acanthodians from the Man On The Hill (MOTH) locality in the Mackenzie Mountains of Canada provide the first unequivocal example of such transitional forms in an Early Devonian (Lochkovian) vertebrate assemblage. The head scales of these specimens are modified with proximity to the mouth to be extremely tooth-like. Three distinct morphotypes of modified cheek and lip scales are described. Their detailed similarity to teeth suggests that they are a result of the same developmental processes, and also suggests the existence of a field of gene expression near the mouth margin in which scales could be transformed into teeth. These transitional forms remove one of the chief objections to the ‘outside-in’ hypothesis for the origins of teeth in vertebrates.

Fishes of the genus Astroscopus are anatomically distinctive within the family Uranoscopidae, mostly because they are characterized by internal nares and are the only marine teleosts known to possess electric organs derived from extraocular muscles. The new world genus Astroscopus contains three extant species from tropical to temperate coastal waters of both sides of the American continent, plus fragmented isolated bones and otoliths of an indeterminate fossil species from the Pliocene and Pleistocene of the Coastal Plain of the eastern United States. Astroscopus countermani, sp. nov., a new stargazer from the Miocene (Tortonian) of Calvert Cliffs (Maryland), is described herein based on well-preserved three-dimensional cranial remains. These cranial remains represent the earliest known skeletal record for the family Uranoscopidae, as well as the earliest occurrence of the genus Astroscopus in the fossil record. Astroscopus countermani is typified by a unique neurocranial appearence, an obliterated orbital foramen, and a prominent ornamented tuberosity arising from the dorsolateral surface of the hyomandibula. Among the anatomical distinctive features of Astroscopus countermani is the relative enlargement of the interorbital portion of the neurocranium (with respect to its extant congeners), which appears to be related to a reduced development of the electrogenic organs. Paleoecological considerations suggest that Astroscopus countermani was a predatory fish that inhabited the subtropical and warm temperate Atlantic marine and paralic waters of North America during the Miocene.

The main objective of this paper is to undertake a detailed re-description of the neotype (skull and lower jaw) and the referred material (postcranial remains) of Niolamia argentina. Additional preparation of this material has revealed previously unrecognized details of the cranial and postcranial skeleton, including the recognition of additional cranial scales, bone sutures, and foramina, the presence of a distinct ornamentation on the skull roof, and the identification of several new inner skull structures. Importantly, the additional preparation shows detailed carotid artery anatomy: the entrance of the carotid artery lies posteriorly in the pterygoids, runs anteriorly and bifurcates into the cerebral and palatine arteries within the basisphenoid, and is not covered ventrally by the pterygoids. In addition, the pterygoids are placed in a ventral position with respect to the basisphenoid and an intrapterygoid slit, a character diagnostic of Meiolaniidae, is present. We corroborate that Crossochelys corniger is a junior synonym of Nio. argentina. Following our preferred phylogenetic hypothesis, South American and Australian taxa related to or belonging to Meiolaniidae and Mongolochelys efremovi from the Upper Cretaceous of Mongolia form a monophyletic group, implying that the origin and diversification of this lineage predated the complete break up of Pangea in the Early to Middle Jurassic. The presence of a ghost lineage between this clade and Cryptodira, extending from the Middle Jurassic to the Early Cretaceous, supports this assessment.

A new specimen of the protorosaur Macrocnemus fuyuanensis, from the Zhuganpo Member of the Falang Formation at Fuyuan (Yunnan Province, southwestern China), is described and compared with Macrocnemus bassanii. The new specimen is the first in the genus Macrocnemus that clearly shows details of the preorbital region of the skull. A large, plate-like lacrimal is located in front of the tall, columnar prefrontal that defines the anterior margin of the orbit. A longitudinally oriented nasal groove extends along the anterior two-thirds of the snout, accommodating the external naris at its anterior part. A similar preorbital depression has previously been described for Dinocephalosaurus and it is also reported here for the first time in Tanystropheus. The new specimen confirms the status of Macrocnemus fuyuanensis as a species distinct from Macrocnemus bassanii on the basis of a humerus that significantly exceeds the radius in length. The occurrence of both Macrocnemus and Tanystropheus in southwestern China further underscores the close faunal affinities of the eastern and western Tethyan realms during the Middle and early Late Triassic.

The South African non-archosauriform archosauromorph Prolacerta and the archosauriforms Proterosuchus, Erythrosuchus, and Euparkeria were important constituents of the Early to early Middle Triassic Karoo ecosystem following the end-Permian mass extinction. We present new data on the osteohistology of these stem archosaurs and provide insight into their paleobiology. Bone tissues of the Early Triassic Prolacerta contain a poorly defined fibro-lamellar complex, with parallelfibered bone in some regions, whereas the contemporaneous Proterosuchus exhibits rapidly forming uninterrupted fibrolamellar bone early in its ontogeny, which becomes slow forming lamellar-zonal bone with increasing age. The early Middle Triassic Erythrosuchus deposited highly vascularized, uninterrupted fibro-lamellar bone throughout ontogeny, whereas the growth of the contemporaneous Euparkeria was relatively slow and cyclical. When our data are combined with those of previous studies, preliminary results reveal that Early and Middle Triassic non-crown group archosauromorphs generally exhibit faster growth rates than many of those of the Late Triassic. Early rapid growth and rapid attainment of sexual maturity are consistent with life history expectations for taxa living in the unpredictable conditions following the end-Permian mass extinction. Further research with larger sample sizes will be required to determine the nature of the environmental pressures on these basal archosaurs.

A skull and mandible of a new species of notosuchian, Caipirasuchus paulistanus, belonging to the Sphagesauridae, were discovered in the rocks of the Adamantina Formation (Bauru Basin: Late Cretaceous). The main autapomorphies are external naris bordered only by premaxillae; very high pterygoids and ectopterygoids; palatines contacting maxillae by a cuneiform process; well-developed oval antorbital fenestra; premaxilla with four teeth; dentary with ten teeth and two diastemata; and one diastema in the premaxilla and another between the fourth alveolus of the premaxilla and the first of the maxilla. Morphological analysis and experimental data suggest an animal with a powerful bite and a dentition with specific regions of action, one adapted to apprehension and the other to food processing.

The earliest ornithischian dinosaurs were small bipeds that possessed the derived, retroverted pubis that is synapomorphic for the clade. Their forelimbs were modified for grasping. Subsequently, ornithischians radiated into numerous body shapes and sizes. Three lineages independently evolved large size and quadrupedality, requiring profound changes to the osteology and myology of the locomotor apparatus. Using comparisons with extinct archosaurian outgroups, as well as extant birds and crocodilians, we reconstruct basal ornithischian limb musculature in order to determine the sequence of musculoskeletal changes that occurred prior to and during the early evolution of Ornithischia. The musculoskeletal anatomy of basal ornithischian forelimbs was probably more similar to that of the crown group archosaur common ancestor and crocodilians than it was to birds. Reduction or loss of the clavicle resulted in migration of the clavicular deltoid onto the proximal scapula and development of a distinct acromial process. The coracobrachialis brevis and supracoracoideus probably protracted the humerus, whereas the scapulohumeralis caudalis and deltoideus scapularis probably retracted it. The deltoideus clavicularis was likely a humeral abductor. In the hind limb, the elongate preacetabular process indicates lateral migration of important femoral protractors to the ilium from an inferred ancestral location on the dorsal vertebrae. The puboischiofemoralis externus was greatly reduced or possibly lost due to pubic retroversion. The reconstruction of basal ornithischian myology provides a baseline for determining the musculoskeletal changes associated with different locomotor modes in ornithischians, and a foundation for biomechanical studies of dinosaur locomotion.

New material of the traversodontid cynodont Dadadon isaloi from the Triassic of southwestern Madagascar is described. The new material consists of a complete, well-preserved skull (FMNH PR 2232) and an unassociated, partial lower jaw (UA 10608). The new material reveals several novel aspects of Dadadon's, morphology. Newly recognized autapomorphies that diagnose Dadadon include a fourth upper incisor with posterior accessory cusp, deep interorbital depressions confined to the frontals, and a very tall, robust mid-frontal ridge. Dadadon can further be distinguished from the similar traversodontids Massetognathus and Santacruzodon by the presence of shorter, broader prefrontals with prominent dorsal depressions, robust anterolateral processes overhanging the orbits, a single cusp in the anterior cingulum of the upper postcanines, and relatively elongate, striated, conical upper incisors. In a revised phylogenetic analysis incorporating data from the new specimens, Dadadon is recovered in a clade with Massetognathus and Santacruzodon. This clade is the sister taxon to the well-supported traversodontid subclade Gomphodontosuchinae. The ‘basal Isalo II’ cynodont fauna from Madagascar is more similar in composition to that of South America than to mainland Africa, although this is probably attributable to the lack of Ladinian—Carnian therapsid fossils on the mainland rather than an actual biogeographic pattern.

The early Eocene genus Tubulodon (Epoicotheriidae) from Wyoming is one of a few primitive genera of the Palaeanodonta that retained tooth enamel. Contemporary Palaeanodon lacked enamel, as presumably did all metacheiromyid palaeanodonts and some derived epoicotheriids. The enamel of Tubulodon is relatively thin and therefore often transparent. Thus, unusual tubes in the orthodentine are often visible. These tubes were initially interpreted as primary dental structures, being pre-stages to the hexagonal dentinal prisms in aardvarks, and inspired the name Tubulodon. Our detailed scanning electron microscopic study showed that individual tubes are surrounded by a hypermineralized rim and enclose a cluster of much smaller elongated structures, or filaments, each residing in a small tunnel. The tubes and filaments do not belong to the natural orthodentine structure and are here interpreted as early post-mortem bioerosional phenomena. Size and morphology of the filaments affiliates them with actinomycetal bacteria. Bioerosional destruction is not unique to Tubulodon. Additional evidence that this is a widespread taphonomical phenomenon comes from numerous specimens of other early Eocene teeth from the Willwood Formation of the Bighorn Basin, Wyoming, as well as diverse mammalian taxa from different stratigraphic levels and geographic locations where we observed varying degrees of tunneling, and even substantial tube development in the dentary itself. In contrast to the orthodentine, the enamel of Tubulodon is not altered. It can be characterized as a primitive stage of radial enamel with substantial interprismatic matrix.

Apatemyids are known from the Paleocene and Eocene of Europe, and the Paleocene to Oligocene of North America, and may share a special relationship with Euarchontoglires. The only endocast previously described for an apatemyid pertains to Carcinella sigei from the late Eocene of France. Here we present a composite virtual endocast of Labidolemur kayi derived from high-resolution X-ray computed tomography data, based on partial crania from the late Paleocene (Clarkforkian) and early Eocene (Wasatchian) of the Clarks Fork Basin, Wyoming. Like C. sigei, L. kayi had voluminous, transversely expansive olfactory bulbs, accounting for approximately 12–15% of the endocranial volume. This is similar to Cretaceous eutherians, but contrasts with the relatively smaller olfactory bulbs in both the basal gliran Rhombomylus turpanensis and in primitive primates (Ignacius graybullianus, Microsyops annectens). Similar to R. turpanensis, I. graybullianus, and the inferred ancestral condition for Microsyops, but unlike C. sigei, L. kayi exhibited exposed caudal colliculi, supporting the inference that this condition was primitive for Euarchontoglires and Euarchonta. The cranial capacity of L. kayi is estimated at 0.5–0.6 cc, yielding encephalization quotient (EQ) estimates of 0.23–0.28 or 0.42–0.50 depending on the equation used. These values are much lower than estimates for C. sigei, suggesting significant increase occurred in brain size in Apatemyidae, perhaps related to elaborations in the family's specialized manual extractive feeding regime. Similarities with primitive primates in EQ and the inferred position of the rhinal sulcus may allow for inferences about encephalization and neocorticalization in the common ancestor of Euarchontoglires.

This paper describes a new assemblage of fossil murids (Mammalia: Rodentia) from an Oldowan archeological site, Hadar, A.L. 894. The dates for the site are well constrained to between 2.35 and 2.9 Ma and the site itself has an estimated age of 2.4 Ma. The A.L. 894 assemblage is the first described from the younger Busidima Formation at Hadar and extends the time range for micromammals at Hadar by 800 ka. The assemblage of 28 specimens has eight taxa represented, a surprising diversity given the sample size. The specimens include a fossil skull of Thallomys, a poorly documented African endemic rodent, as well as one of the earliest occurrences of a small gerbilid, such as Gerbillus in East Africa. Fossil rodents from this time period are important for the interpretation of hominid paleoecology as well as understanding the processes underlying the evolution of ecological communities through shallow, deep-time.

A species of the dugongine dugongid genus Rytiodus from the Miocene (Burdigalian—Langhian; 19–14 Ma) deposits of Jabal Zaltan (= Gebel Zelten), Libya, is re-described, considered a valid species differing from Rytiodus capgrandi from the lower Miocene (Aquitanian) of the Aquitaine Basin (SW France), and named Rytiodus heali. R. heali, together with R. capgrandi and Corystosiren varguezi appear to constitute a taxon of dugongines characterized by broad, mediolaterally compressed, blade-like tusks with enamel mainly on the medial side, and a modified nasal process of the premaxilla. They are regarded as specialized seagrass feeders, using their tusks in excavation of seagrass rhizomes. Rytiodus lived sympatrically with the generalist small-tusked halitheriine dugongid genus Metaxytherium.

The investigation of the evolution and speciation of Equus in Eurasia is, despite the abundance of available material, often hampered by a lack of stratigraphic information. Here we present the results of our study of material belonging to Equus eisenmannae excavated from sequential ‘lower’ and ‘upper’ levels of the loess section at Longdan, China, which has been dated to ca. 2.55–1.85 Ma (early Nihewanian age). The morphological differences between fossils found in the ‘upper level’ and those from the ‘lower level’ were quantified using univariate and multivariate analyses. Quantitative variation among modern Equus is discussed in order to address issues of potential speciation events and evolutionary trends seen in the fossil material. We also discuss the evolutionary level of E. eisenmannae by comparing our sample with E. sanmeniensis. Results show that quantitative differences between fossils of E. eisenmannae from the different levels at Longdan approximate and do not exceed intraspecific variation among modern species of Equus, although the variation is smaller than in the extant species E. hemionus. Thus, no sufficient evidence of speciation within the two sequential levels could be found. However, some common evolutionary trends of modern Equus are evident in E. eisenmannae, even though E. eisenmannae is not considered the immediate ancestor of modern Equus.

Several studies have quantified selective capability in artiodactyls using skeletal correlates such as the premaxillary shape index (PSI), incisor arcade breadth (IAB), incisor arcade curvature (DOC), and incisor width ratio (IWR). These metrics are limited in their applicability because they do not account for the potential importance of muzzle length. Herein we apply a new method for the quantification of muzzle shape (the dentary shape index [DSI]) that combines dentary length and width. We find that browsers possess the longest, narrowest muzzles, whereas the muzzles of grazers are comparatively short and wide. Discriminant function analysis demonstrates that DSI yields the highest rate of correct dietary classification of all muzzle shape proxies proposed to date. Generalized estimating equations and phylogenetically independent contrasts show that the shape of the anterior dentary (DSI) is significantly correlated with both diet and premaxillary shape (PSI) across the cetartiodactyl tree. We suggest that the match between premaxillary and anterior dentary shape is important in cropping but it is the shape of the lower incisor arcade that is under direct dietary selection. We conclude that the length and width of the anterior dentary are functional determinants of selectivity in ruminant artiodactyls and that these traits have potentially evolved in response to selection for efficient feeding as it is related to the different dietary requirements of browsers and grazers.