December 2004

Every Fossil Tells a Story

Professor James Clark Discovers Croc Ancestors in the Crossroads of Asia

By Matthew Lindsay

As he walked the barren, undulating landscape of northwestern China, National Geographic senior editor and amateur paleontologist Chris Sloan was looking for anything out of the ordinary although he wasn’t sure what he would find. He left his rustic campsite early in the morning to scout the area, carefully inspecting the dry earth with each passing step. Something caught his eye. Sloan approached delicately, and saw what appeared to be several bones and a skull. So the story of a fossil discovery begins.

But this story is not all about grand adventure, the thrill of discovery and instant gratification. It is about patience, resolve and painstakingly careful work.

“Big things are relatively easy to find, small things are hard to find. We are looking for small things,” said James Clark, GW’s Ronald Weintraub Associate Professor of Biology.

Clark and internationally recognized dinosaur expert Xu Xing (pronounced Shoo Shing), of Beijing’s Institute of Vertebrate Paleontology and Paleoanthropology (IVPP), have led four expeditions into Xinjiang (pronounced Shin Jang), China, near the Gobi Desert. The expedition team was mainly interested in small dinosaurs that are closely related to birds, however, they discovered a number of interesting fossils of all shapes and sizes.

Sloan made his discovery on the first expedition, during the summer of 2001. He didn’t know it then, but the fossil turned out to be a new species, and an important link in the evolution of crocodilians. Clark, Xu, Yuan Wang of IVPP and Catherine Forster, associate professor of anatomical sciences at the State University of New York-Stony Brook, published their findings from a study of the fossil in the August 2004 edition of the journal Nature. The fossil — named Junggarsuchus sloani (pronounced Jun-GAR-soo-kus Sloan-EYE) in honor of the National Geographic editor — proves that the crocodilians’ skull and crushing jaws developed when the reptiles lived on land, before they evolved into the semi-aquatic creatures we see today.

Why did it take three years to publish these findings? As any paleontologist will tell you, finding a fossil is only half the battle.

Securing the funding and approval to work in China was no easy task. Prior to the expeditions, Clark had to secure financial support and/or permission to explore the site from a laundry list of public and private organizations, including GW, the IVPP, the National Geographic Society, the National Science Foundation, the Chinese Academy of Sciences, the Hilmar Tharp Sallee Charitable Trust, the Jurassic Foundation and the Changji Autonomous Prefecture.

“Working in China is easier now in part because of the new generation of Chinese scientists,” explained Clark. “But Xinjiang is hard to access, both politically and physically.”

Nevertheless, the remoteness of this location also has its benefits. “Most of the world has been fairly thoroughly looked at, but this part of China has really only been explored in the last 20 years,” said Clark.

The fossil Sloan discovered was the most complete skeleton found of a land-based crocodilian from the Middle Jurassic period. Most fossils are incomplete and difficult to excavate, classify and study. Once a fossil is discovered, several steps must be taken to ensure the specimen is safely and securely transported from the field to a lab.

Before excavating a section of the dinosaur bed, researchers will discuss the various options for slicing into the rock and removing the fossil. The difficult terrain of an area like Xinjiang oftentimes makes removing specimens problematic. Clark’s team also is sure to record the GPS position of each fossil. Then, the grunt work begins.

“Removing the rock around the fossil takes the longest amount of time,” said Clark.

The team of researchers in Xinjiang often used jackhammers to quarry the rock around large fossils. After excavating a fossil, the team at Xinjiang would cover it with plaster to protect the fragile cargo on its trip to the lab. Back in the lab, water or weak acids are used to break down the rock around the bones. In some cases, such as with Junggarsuchus sloani, researchers will prepare a specimen using tiny needles under a microscope. After careful preparation the fossils finally may be examined and compared with other fossils, when researchers can find the time.

Although many of the fossils the team unearthed from Xinjiang remain in China, Clark doesn’t have to travel there to study all of the fossils in person. The team’s successful expeditions have created a backlog of specimens, some of which are 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,” said a smiling Clark.

The age of fossils is difficult to determine, because the only means of accurately dating a specimen is to find the age of the rocks surrounding it. To compound the problem, not all rocks can be dated. Luckily, Clark’s team will be able to date the volcanic ash surrounding Junggarsuchus sloani. Lab results on the ash have not yet come back, but based on fossil comparisons Clark estimates the three-foot-long Junggarsuchus sloani fossil to be approximately 150 million years old.

“It solved a problem in the ancestry of crocodilians, but we decided to analyze this fossil first because it was interesting and relatively easy to work on,” Clark admits.

In all likelihood, Junggarsuchus sloani will not be the most important fossil the team finds at Xinjiang. The expedition may even have discovered a new kind of dinosaur. Clark and company are planning to take a closer look at several fossils of baby and adult meat-eating dinosaurs they found. What other discoveries will rise from the dinosaur beds of Xinjiang? Only time will tell.

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