SCIENCE LAB SCULPTS : HERBIVOROUS DINOSAURS

Destroyer of Shins

A sledgehammer for a tail, and a host of rivals to pound.

Many herbivorous dinosaurs were biologically armed to the teeth. Some had skulls studded with horns; others had tails bristling with spikes. But few matched the arsenal of ankylosaurus, a group of herbivores that peaked in diversity during the Cretaceous period

Most of the ankylosaur's body was encased in bony plates that jutted out into jagged points, and some lugged around a sledgehammer-like tail club capable of delivering bone-cracking blows.

Because of their seemingly indestructible nature, paleoartists and researchers alike have spent decades hypothetically pitting these plant-powered tanks against tyrannosaurs and other apex carnivores. But predators may not have been the only creatures they battered.

IN A STUDY in the journal Biology Letters, researchers analyzed the anatomy of one of the world's most complete and ankylosaur skeletons from a species they christened Zuul cruivasator, or  ''Zuul, the destroyer of shins.''

They discovered several broken and healed armor plates concentrated around the creature's hips that lacked any clear signs of disease or predation. Instead, the armor appeared to have been splintered by another ankylosaur's club.

Like today's elk or bighorn sheep, Zuul may have evolved weapons to help it establish dominance within its own species.

''The injuries are right where you'd expect two battling ankylosaurus would break things,'' said Victoria Arbour, a paleontologist of the Royal BC Museum in British Columbia and an author of the study. But they would still have been capable of delivering a debilitating blow below a tyrannosauru's knee.

''The destroyer of shins is still quite apt,'' Dr. Arbour said. [Jack Tamisiea]