August 1, 2003

Find could yield clues about T. rex skin

University of Chicago paleontologist Paul Sereno hopes that a tyrannosaur fossil unearthed a week ago will provide clues to answer that question. "As big as it is, the idea that a tyrannosaur would not have scales but something else is particularly mind-boggling," Sereno said as he and his students encased the fossil in protective plaster last week. The fossil is from U.S. Bureau of Land Management land near the corners of South Dakota and Nebraska. It's the same area where paleontologist Barnum Brown discovered the first Tyrannosaurus rex fossil, in 1900. The bones are embedded in four boulders and possibly a fifth. The largest boulder is about 4 by 5 feet; the smallest a couple feet long. Sereno believes the partial skeleton is that of either a young T. rex or an adult of a smaller tyrannosaur species that so far is known only through teeth from the area.

The Lance Creek Fossil Area, about 200 miles north of Cheyenne, Wyo., has yielded other "mummified" dinosaur fossils that provided evidence about dinosaur skin. "It was not buried as a mummy like the others," Sereno said of the latest find. "But it was buried in such a way that we think the surface of the skin may be preserved for the first time in a large predator." Fossils recently unearthed in China suggest that certain small, predatory, kiwilike dinosaurs had a downy coat, leading some to think that tyrannosaurs--including the fearsome T. rex--might also have had down or feathers of some kind. But that theory is the subject of much dispute among paleontologists.

Ken Carpenter, a dinosaur paleontologist with the Denver Museum of Nature and Science, is skeptical that Sereno's fossil will contain the first skin impressions from a large predatory dinosaur.

"Until he finds it, who knows?" Carpenter said. "There's been small pieces of skin impression, on a relative of T. rex in Canada, that did not show any impression of down." He pointed out how the Chinese fossils came from ancient lake beds. "Unless Paul is digging this fossil out of a lake, I think the chances are very slim," he said.

Sereno believes the tyrannosaur in Wyoming was buried in a flood. The rib cage remains intact, and different types of sandstone can be seen on either side of the ribs. The line between the sandstone types doesn't sag between the ribs, suggesting that the carcass was buried before it began to decay.

Sereno plans to carefully scrape away the rock in a Chicago lab and use a microscope to examine where the skin apparently was. Brent Breithaupt, director of the University of Wyoming Geological Museum in Laramie, said he would be surprised if tyrannosaurs turned out to have downy coats. "There could possibly be some feathers associated with it, but I don't believe it would be completely feather- covered," Breithaupt said. "However, that remains to be seen, and I would be happy to be proven wrong by the fossil record."

A young Tyrannosaurus rex would raise a different question. "If he's dealing with a young animal, do the young animals have a different kind of covering than the adults? A full-grown T. rex might have very little need for feathers if it was able to maintain a constant, stable body temperature," Breithaupt said. "These are all very interesting possibilities, and the fossil record will have to bear out what type of hypothesis is correct."

On the Net:Paul Sereno's Dinosaur Web Site: http:// Denver Museum of Nature and Science: http:// AP