James M. Clark
- Ronald Weintraub Professor of Biology
- Lisner Hall 415
- [email protected]
Areas of Expertise
Fossil vertebrates from the Age of Dinosaurs; crocodylomorphs, dinosaurs, pterosaurs, lepidosaurs; fossils and morphology in evolutionary studies.
Research in my laboratory addresses the evolution of extinct land vertebrates (tetrapods), especially those from fossil deposits of the Age of Dinosaurs (the Mesozoic). This research is grounded in the fossils discovered by expeditions I have organized or been part of, and focuses on the evolutionary relationships of dinosaurs, crocodylians, pterosaurs, and lepidosaurs. Questions addressed by my lab include which extinct groups are most closely related to their living relatives (birds, crocodylians, sphenodontids, squamates, turtles), what the fossils tell us about the transition to the living group, and how fossils inform us about the early evolution of these groups.
Excavating a fossil turtle from the Shishugou Formation, China; former PhD student J. Choiniere at bottom.
My field work has spanned four continents and resulted in the discovery of numerous new species of tetrapods (see below). While I was a college freshman George Callison and I discovered the small vertebrate beds of the Fruita Paleontological Area in the Late Jurassic of Colorado, which continue to produce amazing fossils such as the aardvark-like primitive mammal Fruitafossor. During my graduate studies I spearheaded field work in the Early Jurassic of Arizona with David Fastovsky and Kevin Padian and discovered a rich Middle Jurassic fossil site in northeastern Mexico, where I collaborated with Rene Hernandez, Victor Hugo Reynoso and Marisol Montellano. As a member and co-organizer of the American Museum of Natural History-Mongolian Academy of Sciences expeditions to the Gobi Desert of Mongolia from 1991-2002 with Mike Novacek, Malcolm McKenna, and Mark Norell, I worked with Norell on many of the theropod dinosaurs we discovered, including embryos and nesting adults of oviraptorid dinosaurs. From 2001-2011 Xu Xing and I led extremely successful expeditions to the Middle-Late Jurassic of Xinjiang, China, and I accompanied Xu on his work in the Cretaceous of Inner Mongolia. Other field work included expeditions to Late Triassic marine deposits of Nevada (with H.-D. Sues and N. Hotton), Early Jurassic deposits in South Africa (with J. Kitching and M. Raath), Cretaceous-Tertiary boundary deposits of eastern Montana (with W. Clemens), Early Jurassic deposits of Venezuela (with M. Sanchez-Villagra), Cenozoic deposits of Yemen (with I. Tattersall and P. Whybrow), and Vietnam (with I. Tattersall and J. Schwartz), and Late Jurassic deposits in Utah (with L. Chiappe). Much of this field work and the study of the fossils collected was supported by the National Geographic Society and the National Science Foundation (Earth Sciences).
GWU graduate students J. Chapman and K. Poole excavating Late Jurassic sauropod bones in SE Utah.
Exploration and Discovery
Research in my lab is fueled by discoveries from exploration of Mesozoic deposits around the world. Over a decade of expeditions to the Middle-Late Jurassic Shishugou Formation of Xinjiang, China garnered hundreds of specimens of associated and articulated skeletons, thus far including thirteen new species. Many specimens in this collection remain unstudied, and graduate students are currently studying the paleobiology of the bizarre dinosaur Limusaurus (Josef Stiegler) and the relationships of the enigmatic sauropod Bellusaurus (Drew Moore). Future field work will explore Early Jurassic deposits of South Africa with my former PhD student Jonah Choiniere, and we hope to some day crack the nut that is the Middle Jurassic of the western US.
Shishugou theropods: holotype skeleton of the toothless ceratosaur Limusaurus (top), reconstructed skull (by R.S. Li) of the basal tyrannosaur Guanlong (left), and the skull of the basal alvarezsauroid dinosaur Haplocheirus (right).
Dinosaurs and the Origin of Birds
It is now well established that birds evolved from theropod dinosaurs, and I first delved into this subject in the early 1990s during studies of the theropods collected by the AMNH expeditions to Mongolia. Mark Norell, Peter Makovicky and I began the ThWiG (Theropod Working Group) data matrix (e.g., Clark et al., 2002), which was subsequently modified in many publications and is still being built upon. A major goal of our work in China was to find theropod fossils that would help us further understand the transition from non-flying theropods to birds, and several of our discoveries did just that. Haplocheirus sollers Choiniere et al., 2010, resolved the enigma of Mononykus and its relatives, which had evolved many bird-like features independently of birds. Most surprisingly, the basal theropod Limusaurus inextricabilis Xu et al., 2009, although distantly related to birds, provided important new information on the evolution of fingers in theropods helping to clarify the complex history of digital evolution during the transition to birds.
Skull of a shartegosuchid crocodyliforms from China reconstructed from CT scans by GW undergraduate Alexander Ruebenstahl (lower left), histological section of a shartegosuchid femur showing growth rings processed by J. Stiegler (upper left), and phylogeny of basal crocodylomorphs (Pol et al., 2013).
The Evolution of Crocodylia and Their Fossil Relatives
Crocodylians are the closest living relatives of birds, and the fossil record of the crocodylian limb of the archosaur tree extends back to the early Mesozoic and includes a much greater diversity than those surviving today. My dissertation work was the first quantitative phylogenetic analysis of crocodylians and their many fossil relatives (the Crocodylomorpha), and it identified the major lineages and erected the basic taxonomic structure used today. Subsequent work concentrated on the earliest relatives with the distinctive cranial features of crocodylians (“sphenosuchians” and “protosuchians”), such as Junggarsuchus sloani from the Shishugou Formation (Clark et al., 2004). Current work is focusing on a large sample of shartegosuchids from the Shishugou Formation of China including a growth series of skulls.
Pterosaur phylogeny showing terrestrial (yellow) and marine (blue) taxa (Andres et al. 2014). Our analysis indicates that Pterodactyloidea had a terrestrial origin and then radiated into marine environments.
Beginning with our discovery of a pterosaur skeleton in the Middle Jurassic of Mexico that demonstrated at least some pterosaurs did not walk on their toes (Clark et al., 1998), I have studied several aspects of pterosaur evolution. My former Masters student Brian Andres worked with me on Shishugou pterosaurs, including the oldest known pterodactyloid (Andres et al., 2014), and we showed that current data support a non-marine origin for this predominantly marine group. Our study of a rhamphorhynchid pterosaur, Sericipterus wucaiwanensis Andres et al., 2010, helped to resolve the phylogeny of the basal pterosaurs.
The oldest articulated squamate skeleton, from the Shishugou Formation of China (left) and the tiny skull of the enigmatic Middle Jurassic burrowing lepidosaur Tamaulipasaurus (right).
Lepidosaurs (lizards, snakes, and sphenodontids) have an extensive fossil record, and the Jurassic was an important period for their evolution. Sphenodontids from our work in the Middle Jurassic of Mexico (e.g., Reynoso and Clark, 1998) include some of the closest relatives of the living Sphenodon. Tamaulipasaurus from the same deposits (Clark and Hernandez, 1994) was a burrowing lepidosaur similar to living amphisbaenian and dibamid squamates but represents an entirely new lineage related to squamates but outside the group. Skeletons from the Shishugou Formation of China currently being studied by Jack Conrad, Wang Yuan and Clark are the oldest articulated remains of squamates.
Holotype skull and neck of Tsaagan mangas discovered by Clark at Ukhaa Tolgod, Mongolia.
New Species Discovered or Named by Clark
Mammaliaforms and Tritylodonts:
A.B., University of California, Berkeley, 1978
M.S., University of California, Berkeley, 1985
Ph.D., University of Chicago, 1986
Post-Doctoral Work: Zoology Department, U.C. Davis (1987-1989), National Museum of Natural History (1989-1991), American Museum of Natural History (1991-1994)
Clark, J.M. and R. Hernández 1994 A new burrowing diapsid from the Jurassic of Mexico. Journal of Vertebrate Paleontology 14:180-195.
Norell, M., J.M. Clark, Dashzeveg D., Barsbold R., L.M. Chiappe, A.R. Davidson, M.C. McKenna, Perle A., and M.J. Novacek. 1994 A theropod dinosaur embryo and the affinities of the Flaming Cliffs dinosaur eggs. Science 266:779-782.
Reynoso, V.H. and J.M. Clark 1998 A dwarf sphenodontian from the Jurassic La Boca Formation of Mexico. Journal of Vertebrate Paleontology 18:333-339.
Clark, J.M., J. Hopson, R. Hernández, D. Fastovsky, and M. Montellano 1998 Foot posture in a primitive pterosaur. Nature 391:886-889.
Clark, J.M., M. Norell, and L. Chiappe 1999 An oviraptorid skeleton from the Late Cretaceous of Ukhaa Tolgod, Mongolia, preserved in an avian-like brooding position over an oviraptorid nest. American Museum Novitates 3265, 36 pp.
Clark, J.M., M.A. Norell, and P. Makovicky 2002. Cladistic approaches to the relationships of birds. Chapter 2 in: "Mesozoic Birds; Above the Heads of Dinosaurs," L. Chiappe and L.Witmer, editors, University of California Press.
Kearney, M. and J. Clark. 2003 Problems due to missing data in phylogenetic analyses including fossils: a critical review. Journal of Vertebrate Paleontology 23: 263-274.
Clark, J.M., X. Xu, C.A. Forster, and Y. Wang. 2004. A Middle Jurassic ‘sphenosuchian’ from China and the origin of the crocodylian skull. Nature 430: 1021-1023.
Kirkland, J.M. L.E. Zanno, S.D. Sampson, J.M. Clark, and D. Deblieux. 2005. A primitive therizinosauroid dinosaur from the Early Cretaceous of Utah. Nature 435: 84-87.
Xu, X. J.M. Clark, C.A. Forster, M.A. Norell, G.M. Erickson, D.A. Eberth, C. Jia, Q. Zhao. 2006. A basal tyrannosauroid dinosaur from the Late Jurassic of China. Nature 439: 715-718.
Xu, X., C.A. Forster, J.M. Clark, and J. Mo 2006. A basal ceratopsian with transitional features from the Late Jurassic of northwestern China. Proceedings of the Royal Society of London (B) 273(1598): 2135-2140.
Xu, X., J. Clark, J. Mo, J. Choiniere, C.A. Forster, G.M. Erickson, D.W.E. Hone, C. Sullivan, D.A. Eberth, S. Nesbitt, Q. Zhao, R. Hernandez, C.-k Jia, F-l. Han and Y. Guo. 2009. A Jurassic ceratosaur from China helps clarify avian digital homologies. Nature 459: 940-944.
Andres, B., J. Clark, and X. Xu 2010. A new rhamphorhynchid pterosaur from the Upper Jurassic of Xinjiang, China, and the phylogenetic relationships of basal pterosaurs. Journal of Vertebrate Paleontology 30(1): 163-187.
Choiniere, J., X. Xu, J. Clark, C.A. Forster, G. Yu, and H. Fanlu. 2010. A basal alvarezsaurid theropod from the early Late Jurassic of Xinjiang, China. Science.327: 571-574.
Eberth, D.A., X. Xu, and J.M. Clark. 2010. Dinosaur death pits from the Jurassic of China. Palaios 25: 112-125.
Choiniere, J., J. Clark, X. Xu, and C. Forster. 2010. A basal coelurosaur (Dinosauria: Theropoda) from the Shishugou formation in Wucaiwan, People’s Republic of China. Journal of Vertebrate Paleontology 30: 1773–1796.
Clark, J.M. 2011. A new shartegosuchid crocodyliform from the upper Jurassic Morrison Formation of western Colorado. Zoological Journal of the Linnean Society 163 Supplement 1, S152-S172.
Choiniere, J., J.M. Clark et al. 2013. A juvenile specimen of a new coelurosaur (Dinosauria: Theropoda) from the Middle–Late Jurassic Shishugou Formation of Xinjiang, People’s Republic of China. Journal of Systematic Palaeontology 12(2): 177-215.
Pol, D., O.W.M. Rauhut, A. Lecuona, J.M. Leardi, X. Xu, and J.M. Clark. 2013. A new fossil from the Jurassic of Patagonia reveals the early basicranial evolution and the origins of Crocodyliformes. Biological Reviews 88(4): 862-872.
Brinkman, D.B., D.A. Eberth, X. Xu, J.M. Clark, and X.-C. Wu 2013. Turtles from the Jurassic Shishugou Formation of the Junggar Basin, People’s Republic of China, with comments on the basicranial region of basal Eucryptodires. Pp. 147-172 in: D. B. Brinkman, P. A. Holroyd, and J. D. Gardner (editors), “Morphology and Evolution of Turtles: Origin and Early Diversification”.Springer Verlag, Dordrecht.
Andres, B., J. Clark, and X. Xu. 2014. The earliest pterodactyloid and the origin of the clade. Current Biology 24(9): 1011–1016.
Choiniere, J.N., J.M. Clark, M.A. Norell, X. Xu. 2014. Cranial osteology of Haplocheirus sollers Choiniere et al., 2010 (Theropoda: Alvarezsauroidea). American Museum of Natural History Novitates 3816: 1-44.
Leardi, J.M., D. Pol and J.M. Clark. 2017. Detailed anatomy of the braincase of Macelognathus vagans Marsh, 1884 Archosauria, Crocodylomorpha) using high resolution tomography and new insights on basal crocodylomorph phylogeny. PeerJ 5:e2801; DOI: 10.7717/peerj.2801
Wang, S., J. Stiegler, R. Amiot, X. Wang, G-h Du, J.M. Clark, and X. Xu. 2016. Extreme ontogenetic changes in a ceratosaurian theropod. Current Biology 27: 144-148.
BISC 2333 - Evolution and Extinction of Dinosaurs
BISC 6207 - Current Topics in Systemiatic Biology
BISC 6215 - Vertebrate Phylogeny
BISC 6216 - Morphological Systematics