Asteroid 'didn't kill dinosaurs'
2004-10-12 13:34
Wellington - Dinosaurs were dying out before earth was struck by an asteroid impact that is widely thought to have been responsible for their extinction, two scientists claimed on Tuesday.
Writing in the Trends in Ecology and Evolution monthly, evolutionary biologists Prof David Penny of New Zealand's Massey University and Dr Matt Phillips from Oxford University called for re-examination of the asteroid impact theory.
That theory says that birds and mammals were only able to flourish once an asteroid impact wiped out the dominant dinosaurs and pterosaurs at the end of the Cretaceous period 65 million years ago.
Penny and Phillips agreed the end of the Cretaceous period was marked with an impact, as claimed by geophysicists.
Single piece of evidence
"But after 25 years they have still not provided a single piece of evidence that this was the primary reason for the decline of the dinosaurs and pterosaurs."
"Natural evolutionary processes" made the difference for dinosaurs.
The two men said they believed that mammals and birds, over 20 to 30 million years, started to out-compete dinosaurs, as they began diversifying between 80 to 90 million years ago.
Penny said fossils could tell scientists when the different species of dinosaurs, birds and mammals roamed the earth, which would indicate when the dinosaurs started their demise, and when birds and mammals began to proliferate and diversify.
But the fossil record was patchy, so many conclusions would be tentative.
"So far, this evidence contradicts the popular theory," Penny said.
"The combined evidence from fossils and molecules appears to support an expansion of birds and mammals, and a decline of pterosaurs and dinosaurs, starting many millions of years before the end of the Cretaceous."
The two said that a dogmatic adherence to the popular theory had steered scientists away from examining the real reasons behind the mass extinction.
"I see the discovery of the asteroid impact that marked the end of the Cretaceous as simultaneously a high point, and low point of 20th century science," said Penny.