Stegosaur Plates Used for ID, Not Defense, Study Says

Hillary Mayell
for National Geographic News
May 25, 2005

Scientists have long puzzled over the sometimes bizarre ornamentation found on dinosaurs. Such features range from feathers, bills, and horns to spikes and plates, among others.

A new study of the finlike plates that lined the backs of the Jurassic-period plant-eaters known as stegosaurs suggests that the plates served a rather simple purpose: dinosaur I.D.

Researchers behind the study think stegosaur plates, as well as many structures in other dinosaur species, evolved to help the ancient animals recognize their own kind.

Russell Main, a biologist at Harvard University in Cambridge, Massachusetts, co-authored the study, which is published in latest issue of the research journal Paleobiology.

Referring to many dinosaur families, the biological classification above genus and species, he said, "If you look at [them] from the neck down, their body form is relatively generalized, they're all relatively similar."

"Dinosaurs have come up with a number of weird structures, and people have always wanted to give them interesting and sort of strange functions," he said. "But perhaps the simplest explanation is recognition between groups."

Jack Horner, a paleontologist at the Museum of the Rockies in Bozeman, Montana, joined Main in the study, which was led by Kevin Padian at the University of California, Berkeley.

"The skeletons of these dinosaurs [stegosaurs] below the neck are identical," Horner said. He points to deer as a modern-day analog: While the skeletons of mule deer and white-tailed deer look very similar, the animals themselves have different colors, and their ears and tails are also different.

Horner says these deer attributes serve a similar function to that of the elaborate frills, crests, and back spikes found in dinosaurs. They allow mule and white-tailed deer to identify members of their own species.

Referring to the dinosaurs, Horner noted that "all of these big features on dinosaurs are very expensive" in terms of the energy required to grow them. He added that such features must therefore be extremely important.

Some scientists have theorized that stegosaur plates might have evolved as defense mechanisms, a notion Horner disputes.

"When you think about defense, it's something you don't have to do all the time. Not every animal gets attacked," he said. "But when it comes to species recognition, [that] is something you need all the time. Species recognition is the most important thing, if you're planning to have more stegosaurs."

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