Dinosaur Extinction Didn't Make Way for Us

Mar 29, 07:01 PM

Current Headlines: Scientists have been dumbstruck by new findings that appear to show the mass extinction of dinosaurs 65 million years ago did not make way for the evolution of today's mammals, as previously thought.

For years experts have believed the demise of the dinosaurs paved the way for a flurry of new mammal species, eventually making way for the evolution of man.

But scientists who have constructed a massive family tree for mammals found no sign of an evolutionary burst for the ancestors of today's creatures at the time of the dinosaurs' extinction.

Only mammals with no modern-day descendants seem to have benefited from the dinosaurs' death.

"I was flabbergasted," said study co-author Ross MacPhee, curator of vertebrate zoology at the American Museum of Natural History in New York.

His group's findings were published in yesterday's edition of scientific journal Nature.

At the time of the dinosaurs' demise, mammals were small, ranging in size between shrews and cats. The long-held view has been that once the dinosaurs were gone, they were suddenly free to exploit new food sources and habitats, and as a result they produced a burst of new species.

While the new study says that happened to some extent, it also shows that the new species led to evolutionary dead ends.

In contrast to the failed species, no such burst was found for the ancestors of modern-day mammals such as rodents, cats, horses, elephants and humans.

Instead, the prehistoric ancestors of today's mammals showed an initial burst between 100 million and 85 million years ago, that was followed by another much later burst between 55 million and 35 million years ago.

MacPhee said the new study explains why scientists have been unable to find any relatively modern-looking ancestors for today's creatures from the time of the dinosaurs' demise without any evolutionary boost from the extinction, those ancestors were still relatively primitive and unrecognisable at that time.

Some experts praised the large scale of the new evolutionary tree, which used a controversial "supertree" method to combine data covering the vast majority of mammal species.

It challenges paleontologists to find new fossils that can shed light on mammal history, said Greg Wilson, curator of the Denver Museum of Nature & Science.

William J. Murphy of Texas A&M University, who is working on a similar project, said no previous analysis had included so many mammal species.

But, "I don't think this is the final word," he said.

The study's approach for assigning dates was relatively crude, he said, and some dates it produced for particular lineages disagree with those obtained by more accurate methods.

So as for its interpretation of what happened when the dinosaurs died off, "I'm not sure that conclusion is well-founded," Murphy said.

The study's family tree includes 4,510 species, more than 99 percent of mammal species covered by an authoritative listing published in 1993. To construct it, the researchers combined previously published work that relied on analysis of DNA, fossils, anatomy and other information.

Agencies

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