Brain imaging of dinosaur yields surprise Study suggests it acted like crocodile, not bird

October 23, 1998|By NEWSDAY

Very fine silt that filled a dead dinosaur's skull millions of years ago is shedding new light on the behavior of the Allosaurus, suggesting it acted more like a crocodile than like a bird, scientists announced yesterday.

By using modern CT scan equipment to see inside the fossil material, Scott Rogers, a molecular neurologist at the University of Utah, determined the brain's size and shape. He can also see where blood vessels entered and exited the brain, the complete inner ear and a few other parts of the brain's structure.

"This is the first imaging of what we think is the internal structure of a fossil brain" in such an old, fossilized creature, said Rogers.

"This suggests that Allosaurus, which was always thought to be a bird ancestor, doesn't have a brain that was avian in nature," he said. Allosaurus' brain is far closer to the neural systems seen today in alligators and crocodiles.

The fossil remains represent a carnivorous reptile, Allosaurus fragilis, that lived about 140 million years ago, a 35-foot-long, 2-ton predecessor to the even larger Tyrannosaurus rex. It was found in 1960 in the Cleveland-Lloyd quarry in Emery County, Utah, and has been in storage at the Utah Museum of Natural History, never on public view.

The oval-shaped brain, about 7 inches long and 5 inches high, is roughly the size of a small loaf of bread. What's surprising is that the brain fills only half of the skull, which offers an important clue.

"This neurological configuration looks very close to that of modern-day alligators and crocodiles, and nothing like an avian brain," he explained. In birds -- and also in humans -- the brain fills the skull almost completely, "so this is a very distinguishing feature" suggesting it's an ancestor of the crocodilians. Rogers' report appears. in the current issue of Neuron.

As for birds, Rogers said they probably descended from a different branch of the dinosaur family. Recent finds -- dinosaurs with feathers -- strongly support that idea.

Because of the brain structure in Allosaurus, Rogers said, the animal "probably moved its head fast to snap at things, and it was probably extremely fixed in its behavior, very rigid in terms of what it would do."

So Allosaurus was probably well-adapted to its existing environment, "but couldn't adapt very well to changing conditions," such as the need to find a new food supply. Nonetheless, the species endured a long time, surviving for about 20 million years, he said.

Pub Date: 10/23/98

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