Into the Mouth of the Hadrosaur

Abstract

A dental exam has supplied evidence that Edmontosaurus —one of the most common dinosaurs of the late Cretaceous, some 67 million years ago—chewed unlike any animal alive today. Edmontosaurus belonged to a group of plant-eating dinosaurs called ornithopods. In 1984, researchers studying the sutures between bones in fossil skulls concluded that ornithopods had flexible upper jaws. When the lower jaw clamped shut, they said, the pressure would spread outward from both sides of the upper jaw. The upper rows of teeth would then grind against the lower teeth, rather than slicing as they do in other dinosaurs. Now three paleontologists have acquired the strongest independent evidence yet for this unique jaw motion. Vincent Williams of the University of Leicester in the United Kingdom and colleagues examined microscopic wear patterns on 13 teeth from a 13-meter-long Edmontosaurus found in Wyoming. The dinosaur and its close kin, known as hadrosaurs, had as many as 1000 teeth in multiple rows that moved forward as functional teeth were worn down, says Leicester co-author Mark Purnell. Patterns of tiny scratches on the teeth revealed that the jaws moved just as had been predicted, the team reported last week in the Proceedings of the National Academy of Sciences . “They would have been able to process very tough vegetation,” such as horsetails, says co-author Paul Barrett of the Natural History Museum in London. ![Figure][1] Rows of unerupted teeth in the lower jaw below the chewing surface look like overlapping leaves. CREDIT: VINCE WILLIAMS Paleontologist Lawrence Witmer of Ohio University College of Osteopathic Medicine in Athens calls the study “one of the best microwear papers I've seen.” But he still isn't convinced that the upper jaw could flex. [1]: pending:yes