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A giant asteroid that slammed Earth 65 million years ago, when the dinosaurs ceased to exist, might not carry much responsibility for the extinction of the great beasts, according to paleontologist Kevin Padian.

The curator of the Museum of Paleontology at the University of California, Berkeley, and a professor at that university, Padian spoke Wednesday night at the University of Utah. His was the second of a set of four lectures titled "Dinosaurs!" sponsored by the Utah Museum of Natural History and the Utah Geological Survey.Padian drew upon careful excavations by his university in areas of Alberta, Canada; Montana; and Wyoming. These are among the places where the boundary between the Cretaceous and Tertiary eras is well-preserved.

A layer of iridium deposits right at the end of the Cretaceous period, 65 million years ago, has been discovered throughout the world. The layer is believed by many scientists to be debris left from the asteroid's impact.

Berkeley scientists take a "vacuum cleaner" approach to their digs, carefully examining every type of fossil they come upon. And what they have found gives the lie to popular conceptions of dinosaurs dying off because of the asteroid.

"There was not a mass kill of dinosaurs at the Cretaceous-Tertiary boundary," Padian said.

Dinosaurs did not survive into the Tertiary era, but that doesn't mean the asteroid killed them. According to Padian, only two types of the animals were still alive at the time of the impact.

Once, the animals had been amazingly diverse, with an estimated 16,000 genera that included up to 80,000 species. They were turkey-size or as huge as the 140-foot Supersaurus. They grew spikes, plates and club tails. Some were so immense they needed an extra brain-like ganglion of nerve cells to operate the distant hindquarters.

Yet by the time the asteroid hit, only two types remained, Padian said. By then, dinosaurs had been dying out for millions of years.

Why did they die? According to him, the reason was far more subtle than a mountain dropping in from space.

Population dynamics have two components: the origination rate and the extinction rate. A population of an animal type can be stable while it loses many species, if many more species are evolving at the same time.

Dinosaurs had a high turnover rate, he said. "What is happening at the latest part of the Cretaceous, it seems, is not that the extinction rate is increasing, but that the replacement rate is dropping."

For some reason, new species of dinosaurs were not evolving as they had in the past. Nothing new showed up to replace the species-by-species extinctions that happened over the many millions of years that dinosaurs were dying out.

That's not to say that no asteroid crashed into Earth, in his opinion.

"I think it's probably fair to say an asteroid hit and it had a lot of effects, particularly in the oceans." But many species of animals and plants did survive the impact.

Adding to the stress on species at the time were gigantic volcanic eruptions caused by plate tectonics. The volcanoes happened where India was pushing into the rest of Asia.

Padian's talk was titled "The Real Jurassic Park," and he took the opportunity to comment on the 1993 film's depictions. In many instances, it was accurate. But in others - particularly in the diloph-o-saur-us spitting venom - the movie is based on misconceptions or imagination.

"I think it's a great movie, the acting aside," he said. The reason he likes it isn't that the plot is plausible, but that it shows dinosaurs more realistically than other films.

In the film, a Tyrannosaurus Rex bites through a Toyota Land Cruiser. Speaking of the creature's teeth, he said, "Now, imagine a whole mouthful of lethal bananas. . . . It actually could bite through a Toyota."