A Taste for Dinosaurs

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Taken together, the finds overturn the idea that early mammals were tiny and timid. That had been eroding anyway with occasional discoveries of teeth and bone fragments that hinted at larger creatures. Now paleontologists can stop cooking up theories to explain why mammals were so little--that they had to be small to avoid being found, for example, or they couldn't grow larger because dinosaurs already occupied those ecological niches.

But it's now clear that mammals did fill some of the niches reserved for larger animals. "It's quite possible," says Anne Weil, a Duke University paleontologist who wrote a commentary accompanying the Nature report, "that they competed with dinosaurs for the same prey." And because they ate dinosaurs, she says, they may even have had an influence on dinosaur evolution. What sort of influence? "We don't know," she says. "That's how it is with the best finds. They leave you with more questions than answers." Those answers may be lurking under the barely scratched surface of Liaoning province. --Reported by Andrea Dorfman/New York