New look for an old dinosaur: armor plates all in a row.

New Look for an old dinosaur: Armor plates all in a row

For more than a century, paleontologists have argued about the proper arrangement of the bony plates that stuck out of the back of the stegosaurus, the large, armored dinosaur that roamed the earth 150 million years ago. Some scientists have contended that pairs of these plates were aligned in two matching rows, while other have maintained that the two rows were staggered.

Now a dinosaur artist and paleontologist says he has put this debate to rest by showing that neither approach is correct. Stephen Czerkas, who works with the Natural History Museum of Los Angeles (Calif.) County, believes instead that stegosaurus was crowned by a single row of plates. His work "answers questions that have longbeen bothering people," says James FArlow at Indiana University-Purdue University in Ft. Wayne. Czerkas's explanation also would alter thinking on the plates' role in metabolism.

Most scientists had concluded that stegosaurus had two rows of plates because the upper parts of the plates in the neck and shoulder regions of fossils were found overlapping one another. The bases of these plates are also asymmetric, suggesting to some that another row of plates was required to make the animal symmetric overall. The most complete stegosaurus skeleton, found in North America in 1886, does not have two rows, but because it was missing some of its tail, scientists argued that additional plates must be missing too.

In carefully reexamining this skeleton, however, Czerkas noticed that the plates over the animal's back neither overlap nor have asymmetric bases. Moreover, he says, the bases of the neck and shoulder plates do not overlap at all, so there is no reason to assume that the plates emanated from two rows in this region either. He thinks these neck and shoulder plates, with their thick and asymmetric bases, pointed up and out at an angle so that the animal could move freely.

Czerkas also concluded that the fossil has all of its original plates. The bases "filled out the entire length of the vertebral column perfectly, allowing space for the tail spikes," he says. "The fossil was much more complete than anyone had ever realized."

If Czerkas's findings are correct, scientists will have to revise their pictures of stegosaurs found on other continents and rethink the function of the plates. In his studies, Farlow has found that double rows would have been ideally suited to cooling the stegosaurus by channeling air across its back. This was one line of evidence that led some scientists to think stegosaurs were warm-blooded, according to Czerkas. But with only one row, the plates may have acted as conductors, used more for warming the animal. Other scientists, however, think stegosaurus used the plates to defend itself.