The Missing Piece

James Clark Reconstructs the Evolutionary Puzzle

Biology professor James Clark searches for fossils in Xinjiang, China.

To James Clark, Velociraptors are not just the fast-moving predators that terrorized moviegoers in Jurassic Park; they are links in a chain connecting dinosaurs to modern birds. The Ronald Weintraub associate professor of biology also knows the crocodile’s smile—or, rather, skull and powerful jaws—developed on land long before its swim-adept body. From GW’s labs to the Gobi Desert in China, Clark seeks the missing pieces in the evolutionary puzzle.

“There is nothing as thrilling as uncovering a skeleton of a never-before-seen animal that has been buried for thousands of millennia,” Clark says. “Anticipating a discovery is almost as much fun as the discovery itself.”

On a series of field projects funded by the National Science Foundation and GW’s University Facilitating Fund, Clark has been exploring the Middle to Late Jurassic Shishugou Formation, located in Xinjiang in northwestern China, searching for links between birds and theropod dinosaurs, which are carnivorous bipeds with small limbs. The expeditions, conducted since 2000, have resulted in the collection of many other fossils, including crocodilians, mammals, pterodactyls, and herbivorous dinosaurs.
Clark also has spent 10 years collecting dinosaurs in Mongolia, notably theropods sitting on nests and embryonic dinosaurs in eggs. And his earlier field work in northeastern Mexico also resulted in the discovery of a new species of the flying reptile group Pterosauria.

Now, with a shared $3 million NSF Tree of Life grant awarded in 2002, Clark and research partners are creating an online database of theropod and bird form and structure characteristics. In stocking the database, the researchers are determining the relationships of the major groups of birds and the evolution of their anatomical features involved in their transition from theropod dinosaurs. “The online database will provide virtually every important piece of evidence for what happened during this transition, for all to see,” Clark says.

Some database information will come from a report by Clark and researchers at the University of Utah that was published in May in Nature that details the discovery of a mass graveyard of bird-like feathered dinosaurs in Utah. The previously unknown species, Falcarius utahensis, leaves clues about how meat-eaters related to Velociraptors evolved into vegetarians. While it is not yet known whether the species ate meat, plants, or was omnivorous, it shows the beginnings of features associated with herbivorous dinosaurs, such the expansion of the gut to a size required to ferment plants.

The graveyard was found thanks to a commercial fossil collector who later was convicted of fossil theft. In Clark’s experience, research clues often come from unexpected sources.

During the first of four visits to Xinjiang, his team sought small dinosaur remains relating to their study of the evolution of birds—and left finding an important link in the evolution of the crocodile. Clark co-wrote a study published in Nature in August 2004 stating that while modern crocodiles are semi-aquatic dwellers, its skull and jaws evolved on dry land long before its swim-tuned body. The fossil is the most complete known skeleton of a land-dwelling crocodilian ancestor. The three-foot long creature, believed to have lived about 150 million years ago, was named Junggarsuchus sloani after National Geographic editor Chris Sloan, who found the fossil in 2001 during that first expedition to Xinjiang.

Clark says Junggarsuchus’s skull is similar to the skulls of modern crocodilians, but that its body more closely resembles those of sphenosuchians—a class of slender, land-dwelling crocodilians living from about 230 million to 150 million years ago. Its forelimbs are more adapted to land walking than those of sphenosuchians.

While many of the fossils the team found in China remain there, a backlog of specimens from the four visits is housed at GW. “Even if I didn’t have any more grant funding, there are so many fossils we have already found, there’s decades of work,” Clark says.

In addition to Junggarsuchus slonai, Clark says the expedition may have sparked other significant findings—including several new species of dinosaurs. The Shishugou Formation is one of the world’s few fossil deposits that has preserved dinosaurs from the time when they had just begun to reach enormous sizes and dominate the world’s terrestrial ecosystem.

Clark plans to return to Xinjiang to continue the field work. There are more secrets to be found in the rocks.

—Laura Ewald

To learn more about Clark’s work, visit

back to top

© 2005 The George Washington University
The George Washington University is an equal opportunity/affirmative action institution.