Rewriting the Book on Dinosaurs

Forget what you knew: they weren't necessarily cold-blooded or pea-brained, and may not really be extinct

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If the earliest dinosaurs were meat eaters, how did they evolve into herbivores -- a key to their ability to survive in a variety of environments? The arrangement of teeth and jaws was probably a major factor, and that may explain in part why dinosaurs were so successful overall. Weishampel is trying to correlate tooth design, patterns of tooth wear, the size of the mouth and other aspects of skull mechanics with the types of plants the dinosaurs might have munched. "You can get a rough feeling for how fibrous the material was that they ate, and whether they sheared, ground or pulped their food."

Take sauropods, for example, the four-legged, long-necked giants that flourished in the Jurassic, the middle period of the dinosaurs' reign, which lasted from 208 million to 144 million years ago. These largest of all dinosaurs include Brontosaurus (an out-of-favor name these days: call them Apatosaurus, or risk correction by a knowledgeable six-year-old). They evidently used their spoon-shaped and pencil-shaped teeth to bite off leaves and twigs, relying, like many modern birds, on gizzard stones to do the actual chewing. Horned dinosaurs like Triceratops, which lived toward the end of the dinosaur era, in the late Cretaceous, had very inefficient jaws. "Their teeth were arranged in a vertical plane, which is very unusual," explains University of Pennsylvania paleontologist Peter Dodson. "That essentially means they were eating salad with a pair of scissors."

Weishampel is also using his dental analyses to determine how the advent and proliferation of flowering plants during the early Cretaceous might have influenced population levels of large, plant-eating dinosaurs. There is some evidence, he says, that the spread of flowering plants hurt large-bodied dinosaurs like sauropods and helped the somewhat smaller duck-billed and horned dinosaurs. When flowering plants began to dominate the landscape in the mid-Cretaceous, they edged out the conifers, tree ferns and other plants that the long-established sauropods depended on. The smaller vegetarians, which evolved much later, had not become so set in their eating habits.

Another idea, posited by David Norman, director of the Sedgwick Museum at the University of Cambridge: the giant, established herbivores may have overgrazed their customary food plants, giving the newly evolving flowering plants a chance to compete. Says Norman: "It's rather an exaggeration, but you could say that in a sense dinosaurs might have invented flowering plants."

Dinosaur bones also hold clues to parts of the body that have disintegrated over the eons. By assessing the relationship in living animals between the vertebrae and the delicate nerves they protect, Emily Giffin, a paleontologist at Wellesley College, attempts to make inferences about the neuroanatomy of dinosaurs. Vertebrae are especially revealing because the canal running through them varies in size according to the number of nerve fibers it contains, and that in turn depends on how much the muscles controlled by these nerves are used. Giffin is trying to determine whether theropods -- the dinosaurian suborder that includes fierce predators like Oviraptor, Deinonychus, Velociraptor and Tyrannosaurus rex -- could have used their undersize forelimbs for grasping or whether the arms were purely vestigial.


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