Born too late? A University of Colorado team has unearthed two sets of fossil remains that they say cast doubt on the mass-catastrophe theory of dinosaur extinction. One is a giant cetiosaur, a "whale dinosaur" rarely found in North America; the other is a brontosaurus named Bernice that may have lived a million years after her species is presumed to have died out.

Paleontologist Robert Bakker and colleagues have been digging in a part of Wyoming where rock strata reveal a clear geological chronology. The evidence from that site shows that "every major extinction of dinosaurs occurred in a series of pulses," Bakker said. "The last remains of different families are strewn through millions of years of rock." Thus, the popular notion of a single abrupt and deadly event, such as a meteor collision with Earth, he argues, "is simply not true." Instead, he has found gradual, "stepwise" die-off, both during the dinosaurs' "mid-life crisis" in the Jurassic period, 144 million to 208 million years ago, and during the final extinction cycle some 66 million years ago at the end of the Cretaceous period.

Bakker said Bernice is the first brontosaurus known to have made it into the Cretaceous period, although "our initial reaction was that the animal was stuck in the wrong time zone." As for the 70-foot cetiosaur, the biggest found in Wyoming, it "appears to be the last of its line," Bakker said. "The large dinosaurs tended to get larger before they went extinct."