James M Clark

James M Clark
George Washington University | GW · Department of Biological Sciences

PhD

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159
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Publications

Publications (159)
Article
Jaw muscles are key features of the vertebrate feeding apparatus. The jaw musculature is housed in the skull whose morphology reflects a compromise between multiple functions, including feeding, housing sensory structures, and defense, and the skull constrains jaw muscle geometry. Thus, jaw muscle anatomy may be suboptimally oriented for the produc...
Article
The early-branching crocodylomorph species Notochampsa istedana is known from a single South African specimen collected more than 100 years ago. This species is potentially important for understanding early crocodylomorph evolution, but it is of uncertain taxonomic status and its stratigraphic position is poorly constrained. Here we reinvestigate t...
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Numerous dinosaurian, crocodyliform, and testudine fossils have been recently recovered from the mid-Cretaceous of the Yanji Basin, Jilin Province, China. Among the crocodyliform remains, the specimen (YJDM 00009) described here represents a new genus and new species, Yanjisuchus longshanensis gen. et sp. nov. It is the third Cretaceous crocodylifo...
Article
Sustained miniaturization, here defined as a drop in body size of at least two orders of magnitude from ancestors to descendants, is a widespread and important phenomenon in animals, but among dinosaurs, miniaturization occurred only rarely, once in the lineage leading to birds and once in the Alvarezsauroidea, one of the most bizarre theropod grou...
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Owls and nightbirds are nocturnal hunters of active prey that combine visual and hearing adaptations to overcome limits on sensory performance in low light. Such sensory innovations are unknown in nonavialan theropod dinosaurs and are poorly characterized on the line that leads to birds. We investigate morphofunctional proxies of vision and hearing...
Article
Fossil-rich deposits from the Middle and Late Jurassic of China have yielded a diverse array of sauropod dinosaurs, including numerous species referred to Mamenchisaurus and Omeisaurus. Despite an abundance of fossils and a proliferation of taxa, the anatomy of Middle–Late Jurassic Chinese sauropods remains poorly documented. Here, we comprehensive...
Article
Major evolutionary transitions, in which animals develop new body plans and adapt to dramatically new habitats and lifestyles, have punctuated the history of life. The origin of cetaceans from land-living mammals is among the most famous of these events. Much earlier, during the Mesozoic Era, many reptile groups also moved from land to water, but t...
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Almadasuchus figarii is a basal crocodylomorph recovered from the Upper Jurassic levels of the Cañadón Calcáreo Formation (Oxfordian–Tithonian) of Chubut, Argentina. This taxon is represented by cranial remains, which consist of partial snout and palatal remains; an excellently preserved posterior region of the skull; and isolated postcranial remai...
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Alvarezsaurian dinosaurs, a group of bizarre theropods with greatly shortened and modified forelimbs, are known mostly from the Cretaceous of Asia and South America. Here we report a new alvarezsaurian, Shishugounykus inexpectus gen. et sp. nov, based on a specimen recovered from the Middle–Upper Jurassic Shishugou Formation of the Junggar Basin, w...
Article
Graphical Abstract Highlights d Two new alvarezsaurian dinosaurs are described from Northwest China d They are intermediate between Late Jurassic and Late Cretaceous alvarezsaurians d They showcase the evolution of highly specialized alvarezsaurian forelimb d Specialized alvarezsaurian forelimb morphology evolved slowly, in a mosaic fashion In Brie...
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Shartegosuchids are a poorly known, early-branching group of Asian and North American crocodylomorphs. Shartegosuchids have been hypothesized to have eusuchian-type secondary palates, but a paucity of described material makes assessing this difficult. Our fieldwork in western Mongolia recovered cranial material of a new Shartegosuchus specimen from...
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Bellusaurus sui is an enigmatic sauropod dinosaur from the Middle-Late Jurassic Shishugou Formation of northwest China. Bellusaurus is known from a monospecific bonebed preserving elements from more than a dozen juvenile individuals, including numerous bones of the skull, providing rare insight into the cranial anatomy of juvenile sauropods. Here,...
Article
Ceratopsia includes some of the best-known ornithischian dinosaurs. Many species are erected based on cranial elements alone, and the postcranial skeletons are either missing or undescribed in many taxa. Here we provide the first detailed postcranial description of Yinlong downsi based on the holotype and eight other well-preserved skeletons. Yinlo...
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Background Macelognathus vagans Marsh, 1884 from the Late Jurassic Morrison Fm. of Wyoming was originally described as a dinosaur by Marsh and in 1971 Ostrom suggested crocodilian affinities. In 2005, Göhlich and collaborators identified new material of this species from Colorado as a basal crocodylomorph. However, a partial skull found in associat...
Data
TNT file of the data matrix used in this contribution
Data
Supplementary Information Includes specimen list, character list, additional cladograms depicting the support measures and the synapomorphy list for each node.
Article
Ontogenetic variation is documented within many dinosaur species, but extreme ontogenetic changes are rare among dinosaurs, particularly among theropods. Here, we analyze 19 specimens of the Jurassic ceratosaurian theropod Limusaurus inextricabilis, representing six ontogenetic stages based on body size and histological data. Among 78 ontogenetic c...
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Background Turtles (Testudinata) are a successful lineage of vertebrates with about 350 extant species that inhabit all major oceans and landmasses with tropical to temperate climates. The rich fossil record of turtles documents the adaptation of various sub-lineages to a broad range of habitat preferences, but a synthetic biogeographic model is st...
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Ceratopsia is one of the best studied herbivorous ornithischian clades, but the early evolution of Ceratopsia, including the placement of Psittacosaurus, is still controversial and unclear. Here, we report a second basal ceratopsian, Hualianceratops wucaiwanensis gen. et sp. nov., from the Upper Jurassic (Oxfordian) Shishugou Formation of the Jungg...
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Yinlong downsi, from the Upper Jurassic Shishugou Formation, Xinjiang, northwestern China, is the oldest known ceratopsian dinosaur. Here we provide a detailed description of the skull and mandible based on the holotype, three partial skulls, and disarticulated materials from several other specimens. Yinlong can be diagnosed by six autapomorphies:...
Data
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The dromaeosaurid Linheraptor exquisitus was named in 2010 based on a nearly complete skeleton recovered from the Upper Cretaceous Wulansuhai Formation at the Gate Locality, in Bayan Mandahu, western Nei Mongol, China. However, three recent studies regarded L. exquisitus as a subjective junior synonym of Tsaagan mangas, a dromaeosaurid from the Upp...
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The dromaeosaurid Linheraptor exquisitus was named in 2010 based on a nearly complete skeleton recovered from the Upper Cretaceous Wulansuhai Formation at the Gate Locality, in Bayan Mandahu, western Nei Mongol, China. However, three recent studies regarded L. exquisitus as a subjective junior synonym of Tsaagan mangas, a dromaeosaurid from the Upp...
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The basalmost alvarezsauroid Haplocheirus sollers is known from a single specimen collected in Upper Jurassic (Oxfordian) beds of the Shishugou Formation in northwestern China. Haplocheirus provides important data about the plesiomorphic morphology of the theropod group Alvarezsauroidea, whose derived members possess numerous skeletal autapomorphie...
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The pterosaurs were a diverse group of Mesozoic flying reptiles that underwent a body plan reorganization, adaptive radiation, and replacement of earlier forms midway through their long history, resulting in the origin of the Pterodactyloidea, a highly specialized clade containing the largest flying organisms. The sudden appearance and large suite...
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We describe the anatomy of a new coelurosaurian theropod Aorun zhaoi gen. et sp. nov., from the Middle–Late Jurassic of Xinjiang, China. Histological analysis of the holotype and only known specimen shows that the new taxon is represented by the skeleton of a juvenile individual aged no more than one year. A phylogenetic analysis of theropod relati...
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Extant crocodylians have a limited taxonomic and ecological diversity but they belong to a lineage (Crocodylomorpha) that includes basal and rather generalized species and a highly diverse clade, Crocodyliformes. The latter was among the most successful groups of Mesozoic tetrapods, both in terms of taxonomic and ecological diversity. Crocodyliform...
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The Shishugou Formation in the Junggar Basin was deposited during the late Middle Jurassic to the early Late Jurassic. It is known as a rich source of vertebrate fossils, including specimens of several different kinds of theropod. Here we report an isolated theropod left metatarsal IV (IVPP V 18060) from the upper part of the Shishugou Formation, e...
Article
Extant crocodylians have a limited taxonomic and ecological diversity but they belong to a lineage (Crocodylomorpha) that includes basal and rather generalized species and a highly diverse clade, Crocodyliformes. The latter was among the most successful groups of Mesozoic tetrapods, both in terms of taxonomic and ecological diversity. Crocodyliform...
Chapter
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Five fossil turtle species (?Sichuanchelys sp., three species of Xinjiangchelys, and an indeterminate species of Annemys) are present in the Shishugou Formation (late Middle to early Late Jurassic) of the Junggar Basin, northwestern China. Two of these, X. radiplicatoides sp. nov. and Annemys sp., are each represented by an associated skull and she...
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A small new basal crocodyliform, Fruitachampsa callisoni gen. nov., sp. nov., is represented by several partial skeletons from the Morrison Formation at the Fruita Paleontological Area near Grand Junction, Colorado. It is placed in the Family Shartegosuchidae Efimov, 1988, previously comprising three genera from the Late Jurassic locality of Shar T...
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Reply to “Limusaurus and bird digit identity”
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Sixteen isolated theropod teeth were discovered in two areas in the upper Middle–lower Upper Jurassic Shishugou Formation of the Xinjiang Uyghur Autonomous Region, northwest China. This sample can be divided on the basis of qualitative features and simple quantitative metrics into seven tooth morphotypes, each of which probably represents a distinc...
Article
A new stegosaur species, Jiangjunosaurus junggarensis, gen. et sp. nov., is erected based on a specimen collected from the Upper Jurassic upper section of the Shishugou Formation in the Junggar Basin, Xinjiang, China. It represents the first stegosaur from the Jurassic of Xinjiang and increases the diversity of the dinosaur fauna in the Shishugou F...
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We describe a new coelurosaurian theropod, Zuolong salleei, gen. et sp. nov., from exposures of the upper part of the Shishugou Formation at the Wucaiwan locality, Xinjiang Autonomous Region, People's Republic of China. Zuolong has a large, inclined quadrate foramen that extends onto the medial surface of the quadratojugal, an unusually large fovea...
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We describe a new dromaeosaurid theropod from the Upper Cretaceous Wulansuhai Formation of Bayan Mandahu, Inner Mongolia. The new taxon, Linheraptor exquisitus gen. et sp. nov., is based on an exceptionally well-preserved, nearly complete skeleton. This specimen represents the fifth dromaeosaurid taxon recovered from the Upper Cretaceous Djadokhta...
Article
We describe a new dromaeosaurid theropod from the Upper Cretaceous Wulansuhai Formation of Bayan Mandahu, Inner Mongolia. The new taxon, Linheraptor exquisitus gen. et sp. nov., is based on an exceptionally well-preserved, nearly complete skeleton. This specimen represents the fifth dromaeosaurid taxon recovered from the Upper Cretaceous Djadokhta...
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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...
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The fossil record of Jurassic theropod dinosaurs closely related to birds remains poor. A new theropod from the earliest Late Jurassic of western China represents the earliest diverging member of the enigmatic theropod group Alvarezsauroidea and confirms that this group is a basal member of Maniraptora, the clade containing birds and their closest...
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Three newly discovered bonebeds from the Shishugou Formation of Xinjiang, China, are unusual in preserving vertically stacked and articulated to associated skeletons of at least 18 small, non-avian theropod dinosaurs in pits that are 1-2 m deep. The pits host a soft sediment-deformed mixture of alluvial and volcanic mudstone and sandstone. There is...
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Gigantic, ferocious, long-dead animals like Tyrannosaurus rex never fail to capture people's attention, and the discovery of a new tyrannosaur—giant or otherwise—is always big news. On page 418 of this issue, Sereno et al. (1) report on a spectacular skeleton of a new genus and species near the ancestry of the group including T. rex and its closest...
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The troodontid Byronosaurus jaffei is known from two specimens from adjacent localities in the Nemegt basin, Omnogov Aimag, Mongolia. These specimens are composed of well- preserved cranial material and fragmentary postcrania. All of these elements are described here. Byronosaurus jaffei is included in a comprehensive phylogenetic analysis of Coelu...
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We describe the skull of the holotype of Citipati osmolskae, one of the best preserved oviraptorid skulls known. The skull preserves stapes and epipterygoids, and the mandible preserves a slender coronoid bone, none of which has been reported before in oviraptorids. The braincase is similar to that of other basal coelurosaurs but possesses extensiv...
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An embryonic oviraptorid skeleton is described within an egg from the Late Cretaceous Djadokha Formation of Ukhaa Tolgod, Mongolia. The specimen comprises the ventral part of the skull and most of the mandible, a poorly preserved axial skeleton missing most of the tail, and portions of the forelimbs, shoulder girdles, pelvis, and hindlimbs. The sku...
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A new genus and species of Tritylodontidae, Yuanotherium minor, is described and compared with other known tritylodontids. The new taxon is represented by a partially preserved upper jaw with three postcanines, collected from the upper part of the Shishugou Formation (Oxfordian, Late Jurassic) in the Wucaiwan area of the Junggar Basin, northwest− e...
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We review the morphology, taxonomy, and phylogenetic relationships of the upper Cretaceous Mongolian troodontid Saurornithoides. Saurornithoides mongoliensis is known only by the holotype from Bayan Zag, Djadokhta Formation. This specimen includes a nearly complete, but weathered, skull and mandibles, a series of dorsal, sacral, and caudal vertebra...
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Theropods have traditionally been assumed to have lost manual digits from the lateral side inward, which differs from the bilateral reduction pattern seen in other tetrapod groups. This unusual reduction pattern is clearly present in basal theropods, and has also been inferred in non-avian tetanurans based on identification of their three digits as...
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Dinosaurs have captured the popular imagination more than any other extinct group of organisms and are therefore a powerful tool in teaching evolutionary biology. Most students are familiar with a wide variety of dinosaurs and the relative suddenness of their extinction, but few are aware of the tremendous longevity of their time on Earth and the r...