D i n o s a u r

The Real Jurassic Park
A fossil bonanza in northwestern China shows that the ancestors of T. rex and other reptile giants started small.
By Peter Gwin
National Geographic Staff
Photograph by Ira Block

Perhaps the shriek of a dying animal enticed the dinosaur into the trap. Or maybe it was the scent of rotting flesh. Whatever the bait, once the predator was lured into the mud pit, it quickly forgot its prey. It thrashed futilely in the mire for a long while, but its legs couldn’t reach the bottom. Doomed, the animal slowly accepted its fate and succumbed to exposure, but not before its struggle attracted another predator to the pit, continuing the cycle of the death trap. Eventually the mud turned to stone, entombing its victims, stacked one on top of another, for 160 million years.
This is the story contained in a column of rock unearthed in northwestern China’s Junggar Basin. But that column is just part of a startling collection of fossils excavated over the past seven years by paleontologists James Clark and Xu Xing with support from the National Geographic Society. Their discoveries are opening a new window onto an obscure period in Earth’s geologic history—a violent interval that lasted from about 165 to 155 million years ago and saw the continents breaking apart and dinosaurs undergoing a burst of evolution. As landmasses divided and animals became isolated from each other, a profusion of new branches sprouted on the dinosaur family tree. These new branches eventually yielded many famous dinosaur groups, including horned ceratopsians, armored stegosaurs, and tyrannosaurs. But the dearth of terrestrial fossils from this ten-million-year span had vexed scientists. “We could trace these groups back through time to this period, but then the trail went cold,” says Clark, a professor at George Washington University.
In 2000 Clark joined Xu (pronounced shoe), a rising star at Beijing’s Institute of Vertebrate Paleontology and Paleoanthropology, for a scouting trip to the Junggar Basin. The following year the two scientists mounted a full expedition to the basin’s Shishugou formation, one of the few places on Earth where the exposed rock dates to the Middle Jurassic. Some 160 million years ago it was a marshy realm at the foot of a small mountain range riddled with volcanoes. Now it is a series of desiccated badlands and dunes splayed along the Gobi desert’s western edge.
“We intentionally chose an area where I had seen a lot of small fossils,” says Clark, noting that small prehistoric species tend to be rare, more difficult to find than large creatures. The excavation of one massive skeleton, like that of a multi-ton sauropod, can take an entire field season, Clark says. Instead, he and Xu focused on quantity, a strategy they hoped would yield plentiful clues about the missing segments of the dinosaur panorama.