Long bones of the temnospondyl Metoposaurus diagnosticus krasiejowensis from the Late Triassic of Krasiejów, Poland, were studied using histological analysis. Six femora, three humeri, a radius, and an ulna were prepared for thin-sectioning. In all bones, the dominant type of primary bone matrix is parallel-fibered bone with secondary, or rarely primary, deposition of lamellar bone inside vascular canals. Two small humeri and the smallest femur showed incipient fibrolamellar bone, which may be a character typical for juvenile individuals. The medullary region is filled with well-developed trabecular bone. The growth marks in all bones are organized as thick layers of highly vascularized zones and thick compact annuli with numerous rest lines, which may correspond with favorably wet and long, unfavorably dry seasons. The thickness of the annuli is similar to the thickness of zones for reasons still unknown. Based on the highest estimated number of growth cycles in the femora, the long bones from Krasiejów all belong to juvenile animals. High amounts of Sharpey's fibers are very characteristic in all described bones. A new interpretation of mode of life is proposed based on these findings: the extremely flat skull, the relatively short and wide humerus, large manus, and limbs with strong muscles suggest that this species might have been able to burrow underground during the long unfavorable part of the year.

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An exceptionally well-preserved specimen of a batoid from the Turonian (Late Cretaceous) of Morocco has been named as †Tingitanius tenuimandibulus, sp. nov. The fossil has been identified as a member of the Platyrhinidae and represents the oldest known example of a thornback ray. Mechanical and acid preparation of the ventral surface has revealed the general body form of the specimen and permitted teeth and three morphotypes of dermal denticles to be extracted. Computed tomographic (CT) scanning of the chondrocranium and thoracic region has allowed the detailed study of the skeletal elements concealed within the rock. The phylogenetic position of the new specimen and implications for the phylogenetic positions of the ‘rhinobatoids’ are discussed. †Britobatos, gen. nov., is erected to accommodate †Raja primarmata which is here shown to be a sister taxon to the Platyrhinidae including †Tingitanius. It is likely that reassessment of isolated batoid teeth from the Cretaceous and Paleogene will confirm the former importance of the Platyrhinidae.

A new species of hump-backed semionotiform fish, Lophionotus sanjuanensis, gen et sp. nov., is described based on specimens recently and previously collected from the Upper Triassic Church Rock Member of the Chinle Formation of southeastern Utah. It is characterized by a deep body with a large postcranial hump, and dense tuberculation on the posterodorsal margin of the skull that continues into the dorsal ridge and dorsolateral flank scales. The vertical preoperculum bears a short and broad paddle-like ventral process. The infraorbital series expands ventral to the suborbital and contacts the anterior ramus of the preoperculum, although this character has also been observed in other deep-bodied semionotiform taxa. This taxon represents the first newly described semionotiform fish species from the western United States in over 45 years, and adds to knowledge of Triassic fishes biodiversity.

The first fossil specimen of the characiform genus Salminus is described here. The material, a threedimensionally articulated head, is very well preserved and allowed us to identify a new species. We could study both outer and inner bones. The specimen was found in the locality Toma Vieja, northeast of the city of Paraná, central eastern Argentina. The bearing horizon is the so-called ‘Conglomerado osífero,’ which is putatively included in the lowermost beds of the fluvial Ituzaingó Formation. The ‘Conglomerado osífero’ is early Tortonian (early late Miocene) in age. Recent species of Salminus are top-ranking pelagic predatory fishes in temperate to tropical lowland freshwaters of South America. The aquatic vertebrate fauna occurring in the bearing bed shows a similar composition to several northern South American units such as the Urumaco Formation (Venezuela, late Miocene) and La Venta Formation (Colombia, middle Miocene).

The holotype of the large temnospondyl Calamops paludosus is the oldest known tetrapod fossil from the Triassic of the Newark basin in Pennsylvania. Although it is usually placed in Metoposauridae, its affinities have remained unknown since its original description because the unique specimen had never been prepared. Preparation and casting of the specimen, which comprises three pieces of a left mandibular ramus, now permits detailed anatomical description of the jaw and assessment of its affinities. Calamops paludosus is a valid taxon of trematosauroid temnospondyls that can be diagnosed by several autapomorphies. It represents one of the geologically youngest known records of long-snouted trematosaurs and the first record of these temnospondyls from the Late Triassic of North America.

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This paper describes a new species of the genus Adocus (A. inexpectatus, sp. nov.), based on an almost complete shell from the upper Eocene Youganwo (= Youkanwo) Formation of the Maoming Basin, China. The inclusion of A. inexpectatus in a phylogenetic analysis of Adocusia resulted in a polytomy with Adocus aksary and A. amtgai (both from the Upper Cretaceous of Asia). This clade formed a polytomy with the North American species of Adocus. Like other ‘true’ Adocus, A. inexpectatus has overlapping of the marginals onto the costals in the middle and posterior parts of the carapace and sculpturing of the shell surface with small grooves and pits. Thus, A. inexpectatus represents the first ‘true’ Adocus from the Paleogene of Asia. Other specimens from the Paleogene of Asia that have been referred to Adocus, characterized by shell sculpturing with small dots and unknown condition of the marginal/costal overlapping, are distinct from ‘true’ Adocus and herein referred to as ‘Adocus’ spp. Here we also report the presence of ‘Adocus’ from the Paleocene of North America. Our study indicates that the evolutionary and biogeographic history of the Adocidae was more complicated than considered previously, including previously unrecognized dispersal events between Asia and North America.

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The late Campanian—aged (= Judithian) squamates from the Terlingua Local Fauna of the Aguja Formation, southern Texas, includes four scincomorphans: a new taxon (Catactegenys solaster, gen. et sp. nov.), referable to Xantusiidae, that has massive teeth and tooth crown morphology similar to that of contogeniid lizards; an indeterminate scincomorphan (Apsgnathus triptodon, gen et sp. nov.) with robust teeth; and two unnamed scincomorphan morphotypes. Anguimorphans in the fauna include Odaxosaurus piger, cf. Parasaniwa wyomingensis, and a likely xenosaur. Ophidian jaw fragments confirm the presence of a snake in the fauna. The Aguja squamate assemblage is one of the most southerly of a series of paracontemporaneous squamate faunas extending from central Alberta to northern Mexico. Comparison of these faunas reveals that, although two taxa are endemic to the Aguja Formation, others show some latitudinal trends. Odaxosaurus and Parasaniwa are present in all well-sampled faunas from Alberta to Texas. The mammal-like Peneteius and snakes are found only in faunas from southern Utah to Mexico. Chamopsiids are only present from Alberta to New Mexico. The sole representatives of Contogeniidae and Xantusiidae are restricted to southern Utah and southern Texas, respectively. These hypotheses of distributional patterns must continue to be tested through ongoing investigations of all of the relevant faunas from the late Campanian of the Western Interior.

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Madtsoiidae are a group of archaic snakes, widely distributed in the Upper Cretaceous of Gondwanan landmasses (South America, Madagascar, India, Africa), but otherwise reported outside Gondwana based only on scarce material from a few southern European localities. Here, we describe associated snake remains from uppermost Cretaceous (Maastrichtian) beds of the Hajeg Basin, Romania, as a new small-madtsoiid taxon, Nidophis insularis, gen. et sp. nov. Nidophis, represented by a large number of well-preserved vertebrae and ribs that apparently belonged to one individual, is one of the best-known Cretaceous madtsoiids, and the most completely documented member of the family from Europe. Phylogenetic analyses place the new taxon within a moderately supported Madtsoiidae, closely related to Herensugea from the Upper Cretaceous of Spain. The two European taxa, together with other small madtsoiids, are recovered as the sister taxon to a second madtsoiid clade including large-to-gigantic forms such as Madtsoia, Wonambi, and Yurlunggur. The presence of these small madtsoiids, together with that of Menarana, in the uppermost Cretaceous of Europe, suggests that early widespread distribution of madtsoiids, extending over the southern part of Europe, instead of late northward immigration from Gondwanan landmasses, as proposed previously, might account for the paleobiogeographic distribution of Cretaceous Madstoiidae.

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A new protorosaur is described on the basis of a single specimen from the Ladinian of southern China. Although it has been greatly crushed, it still preserves clear details of the skull and axial skeleton. It possesses a neck that is longer than the trunk and is similar to tanystropheids in having 12 or 13 cervicals. Unusual among protorosaurs, the new form has an elongate snout. It also lacks a clear thyroid fenestra, although there is a slight separation of the pubis and ischium close to the pubic symphysis. The new form adds to the growing diversity and disparity of protorosaur taxa from the Middle Triassic of southern China.

Recent discoveries have shown that non-dinosaurian dinosauromorphs were morphologically diverse, globally distributed, and have a stratigraphic range extending into the Upper Triassic. Silesauridae, the sister group to Dinosauria, contains at least seven species. Here we describe Lutungutali sitwensis, gen. et sp. nov., the first silesaurid from the upper portion of the Ntawere Formation of the Luangwa Basin, Zambia. The upper Ntawere Formation has been correlated with subzone C of the Cynognathus Assemblage Zone of the Karoo Basin in South Africa and the Lifua Member of the Manda beds in the Ruhuhu Basin in Tanzania, both of which are considered Anisian in age and the latter has yielded the silesaurid Asilisaurus kongwe. The results of our phylogenetic analysis, including a new pelvic character, allies Lutungutali with Upper Triassic silesaurids such as Silesaurus, Sacisaurus, and Eucoelophysis rather than with the possibly coeval Asilisaurus. The Zambian silesaurid shares a laterally oriented brevis fossa on the ilium and a transversely thin ischium in cross-section with Upper Triassic forms. Silesaurids were more diverse during their early evolution in the Anisian than previously suspected. Lutungutali and Asilisaurus are the two oldest known members of the bird-line archosaurs represented by body fossils. Together they show that a subclade of bird-line archosaurs was diversifying soon after its origin, building further support for the rapid diversification of Archosauria in the wake of the Permo-Triassic extinction.

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The transition from basal sauropodomorphs to sauropods is one of the most dramatic evolutionary transformations in the history of dinosaurs. Constituent taxa of this transition were recorded mainly in South Africa and South America, and to a lesser extent in North America. We describe here the postcranial anatomy of four specimens of basal sauropodomorphs from the Late Triassic of Patagonia, Argentina, and identify them as adult individuals of Mussaurus patagonicus. The material is composed of one subadult and three adult specimens and was originally identified as Plateosaurus. The completeness of the material provides more complete knowledge of this taxon and allows us to introduce aspects of basal sauropodomorph anatomy that were poorly understood until now, such as the configuration and arrangement of the distal carpal elements. The phylogenetic relationships of Mussaurus patagonicus are tested through a cladistic analysis of basal sauropodomorphs based on the anatomy of these specimens rather than on the post-hatchling and juvenile specimens previously known for this taxon. Mussaurus is recovered as a non-sauropod anchisaurian, being the sister group of Aardonyx plus more derived sauropodomorphs and is depicted outside the ‘quadrupedal clade,’ given the presence of plesiomorphic features such as a humerus/femur ratio <0.8, a curved femoral shaft in lateral view, and a nearly circular femoral midshaft cross-section. Mussaurus patagonicus adds new and valuable information that helps to clarify the core of the basal sauropodomorph-sauropod transition.

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Polar dinosaurs provide unique insights for testing hypotheses regarding paleobiology, paleoecology, and paleobiogeography. Critical for such testing is a comprehensive understanding of the taxonomic diversity of contemporaneous polar and lower-latitude paleofaunas. Here we determine the taxonomic identity of a theropod metatarsal that was discovered in the Upper Cretaceous Prince Creek Formation on the North Slope of Alaska. Its morphology and size are most consistent with a metatarsal IV of an ornithomimosaurian or a juvenile tyrannosaurid. Long bone histological analysis reveals a bone tissue composed of fibrolamellar matrix with a mosaic of laminar, longitudinal, sub-plexiform, radiating, and reticular vascularization patterns. The spacing between two outer growth lines diminishes near the periosteal surface, suggesting that the individual was near somatic maturity at the time of death. This finding suggests that its adult body size was comparable to contemporaneous North American ornithomimids, such as Ornithomimus, and much smaller than those of known tyrannosaurids. Thus, we ascribe the Alaskan specimen to Ornithomimosauria, providing new evidence on the known taxonomic diversity of the Prince Creek fauna. Interestingly, the Alaskan specimen primarily shows annuli, which is inconsistent with the pronounced lines of arrested growth (LAGs) reported in the purported southern high-latitude ornithomimosaurian Timimus and observed variably in contemporaneous lower-latitude ornithomimids. Due to this inconsistency, additional dinosaurian specimens are needed to comprehensively examine the relevance of particular histological features to polar climate habitation.

We describe the anatomy and bone histology of an enantiornithine specimen from the Early Cretaceous Jehol Group of northeastern China. CNUVB-0903 is larger than most Early Cretaceous enantiornithine birds and also different from all other named taxa. Thus, we erect the new species Zhouornis hani for the new specimen. CNUVB-0903 preserves a suite of new morphologies for the clade. Noteworthy are those of the braincase and occipital region of the skull, which was previously poorly known for enantiornithines. The morphology and placement of the large basipterygoid processes and the well-developed basisphenoid recess—comparable in morphology to those of non-avian dinosaurs—highlights the evolutionary conservatism of the enantiornithine skull. The histological characterization of CNUVB-0903 indicates that it was not yet a full-grown individual at the time of death. This, combined with the comparatively large size of the skeleton, supports previous evidence indicating that early in their history, enantiornithines were able to achieve relatively large sizes.

Partial eggs from the Eocene Willwood Formation of Wyoming contain unidentifiable embryonic remains; the eggs are referable to a theropod on the basis of their structural layering of calcite and to an avian theropod because of their Eocene age. We assign the specimens to the oofamily Medioolithidae as Microolithus wilsoni, oogen. et oosp. nov., on the basis of the following unique combination of characters: 600-µm-thick eggshell composed of three structural layers; abrupt and undulating contact between the mammillary and continuous layers; smooth and glossy outer egg surface; faint or obscure prisms of the continuous layer; non-branching pores; and mammillary-to-total shell thickness ratio of 1:4. The eggshell microstructure resembles that of some extant neognath bird eggs. We refer a single egg from Chadron Formation of eastern Nebraska to incertae sedis as Metoolithus nebraskensis, oogen. et oosp. nov. A combination of characters distinguishes the egg from other fossil and modern avian eggs, namely, thicker eggshell, prominent ornamentation, flared upper portion of the prisms, variable mammillary thickness, and irregular squamatic texture in the continuous layer. These characteristics more closely resemble Mesozoic non-avian theropod eggs and likely reflect mosaic evolution in the non-avian to avian-theropod transition. Finally, an external layer occurs in a wide range of Paleogene and Cretaceous eggs of variable size and taxonomic affinities, indicating that this feature may not represent an apomorphic character for the avian crown group with respect to non-avian theropod eggshell. Therefore, an external layer cannot be used to identify neognath birds in the Mesozoic.

The craniodental anatomy of Machairodus catocopis is assessed through the study of a well-preserved specimen from the early Hemphillian site of Sebastin Place (Kansas) and through comparisons with other Miocene American and Eurasiatic machairodonts, in order to resolve its affinities and to gain a clearer understanding of the evolution of machairodontine felids in the Holarctic. In view of the similarities with the Old World species Machairodus aphanistus, the original generic assignment seems correct, and later attribution of this species to the genus Nimravides appears unjustified. Similarities with Old World Miocene homotherins are too extensive to be the result of convergent evolution, especially considering the mosaic evolution of different machairodont adaptations. Hypotheses suggesting that M. catocopis is a part of a native American lineage originating from a feline, rather than machairodontine, immigrant are unjustified on anatomical or evolutionary grounds. The succession of sabertoothed felid species in the American Miocene is best explained as the result of three immigration events. A first immigration of a felid of Pseudaelurus grade led to the evolution of primitive species such as Pseudaelurus intrepidus and Nimravides pedionomus. A second immigration of a species of Machairodus aphanistus grade around the time of the ‘Hipparion event’ would result in the evolution of M. catocopis. The late Hemphillian species ‘Machairodus’ coloradensis is clearly a member of the Old World Turolian Amphimachairodus lineage, and would be the result of a third immigration event.

Increased field collecting over the last few years, combined with the examination of historical collections in Uruguay, has resulted in the discovery of a great number of specimens of the Scelidotheriinae, indicating that this subfamily is better represented in Uruguay's Pleistocene fauna than previously thought. Because much of this new material is diagnostic, in this work we provide a fuller description of some specimens (a skull with associated mandible and the manus, another almost-complete skull, and two partial dentaries) from the late Pleistocene of Uruguay for which only preliminary descriptions have been previously made, with tentatively assignments to Catonyx. A discriminant analysis was performed using 48 adult specimens including Scelidotherium, Catonyx, and Proscelidodon and supports the contention that Catonyx is a valid genus and the inclusion of these new specimens within this genus. This analysis also allows us to identify those cranial characters that better differentiate the genera. The variables involved in the discriminant analysis are those related to the length of the skull, whereas variables related to the width have been excluded from the models or when included have had little significance to the analysis. We provide new optically stimulated luminescence (OSL) dates in the range of 16–32 ka that confirms the late Pleistocene age of the Dolores Formation, the source of these specimens. The described remains represent the first record of Catonyx cuvieri in Uruguay and the first evidence for the presence of the species outside Brazil.

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A skull and a partial skeleton of a large late Pleistocene megalonychid sloth recovered from a cave on Cerro Pintado, Sierra de Perijá Mountain Range, a branch of the northern Andes, in Zulia State, Venezuela, is described as a new genus and species, Megistonyx oreobios. A cladistic analysis of the new taxon based on cranial characters indicates that it is closely related to Ahytherium, another late Pleistocene megalonychid from South America known from cranial remains, and suggests that there may have been at least two distinct clades within the family since the late Miocene. Megistonyx oreobios is one of a number of extinct sloth taxa found at high elevations in South America and suggests that many extinct sloth taxa were not as thermally sensitive as their modern relatives and were capable of living under colder climatic conditions.