Harrisburg scientist rebuts idea that asteroid killed dinosaurs 'It's an exciting theory, but it's wrong,' he argues

August 20, 1998|By KNIGHT RIDDER/TRIBUNE

PHILADELPHIA - It's popular in some circles to believe a huge asteroid crashing into the earth caused the dinosaurs to become extinct. "It's an exciting theory - but wrong," contends paleontologist Robert M. Sullivan, who works at the Pennsylvania State Museum in Harrisburg.

Sullivan was in Philadelphia recently to address a seminar on "The Many Myths of Dinosaur Extinction" at Dinofest, a dinosaur exhibit. "We don't know why the dinosaurs disappeared," he said, "but we can say unequivocally it was not an asteroid.

"Geologists make a convincing case that an asteroid hit the earth towards the end of the Mesozoic era," when dinosaurs were about, he said, "but that doesn't prove its effects wiped out the dinosaurs.

"Why would it eliminate dinosaurs but not other species alive at the same time? That doesn't make biological sense."

It also doesn't explain the number of dinosaur species that had already become extinct before the fateful asteroid fell. The notion that all dinosaurs disappeared together is just another extinction myth, Sullivan said. In fact, the number of dinosaur species continuously declined, he explains. Apatosaurus, for example, was extinct 65 million years before Tyrannosaurus vanished.

"The data is there," he said. "But some choose not to look at it."

Paleontologists find fossils of a particular type in rock layers dating to the Triassic portion of the Mesozoic Era (190 million-225 million years ago), for example, that are not found in the rock of the Jurassic (140 million-190 million years ago) and Cretaceous (65 million-140 million years ago) periods. And fossils dated to those later periods indicate that different species of dinosaurs had appeared by then.

Sullivan says there were only 17 dinosaur species left by the end of the Cretaceous.

He thinks people prefer the asteroid-did-it theory because it's "black and white, a quick and dirty fix that's easier to relate to than trying to work out a variety of complex factors that affected evolution."

The more complex evolutionary tale of dinosaurs sees birds as a key link from one era to another.

This theory was first propositish paleontologist Thomas Huxley in 1868, Sullivan said, but only in the past 10 to 15 years have researchers been making a solid case for it by finding intermediate forms.

Pub Date: 8/20/98

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