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Dinosaur Variety Couldn't Save Them

Posted on: Friday, 19 November 2004, 07:00 CST

Mass extinctions and climate change have shaped the direction of evolution, but are variety and diversity enough of a hedge against sudden change. Apparently not, at least for the great dinosaur extinction, according to research that points to their large diversity during the last mass extinction.

Astrobiology Magazine -- When dinosaurs became extinct from the effects of a massive asteroid hitting Earth 65 million years ago, there were more varieties of the reptiles living than ever before, according to a new analysis of global fossil records by a team of researchers led by a University of Rhode Island paleontologist.

"Our analysis finally lays to rest the old, utterly unsupported idea that dinosaurs were declining in diversity during the last 10 million years of their time on Earth," said David Fastovsky, URI professor of geosciences.

Fastovsky's analysis, published in the October issue of Geology, found that early dinosaurs from the late Triassic period comprised only 40 known genera, but diversity dramatically increased throughout the time dinosaurs were on Earth, skyrocketing in the Cretaceous period -- 99 to 65 million years ago -- when at least 245 dinosaur genera lived.

"Dinosaur diversity was increasing logarithmically throughout their 160 million years on Earth," said Fastovsky, who is conducting research at the National Autonomous University of Mexico through July 2005 as a Fulbright Scholar. "Their increasing diversity seems to have been fueled by the evolution of new innovations that allowed them to explore new habitat."

According to Fastovsky and his co-authors, early dinosaurs tended to be unspecialized, but during the late Cretaceous period they became much more specialized in their feeding and behavior patterns, driving their evolution into more and more genera. The diversity of plant-eating dinosaurs in the Cretaceous was found to be especially high.

"The ability to colonize heretofore unavailable ecospace by the invention of new feeding mechanisms and behaviors may have been a key driving force in the striking and continuous Jurassic-Cretaceous dinosaur diversification," the researchers wrote in Geology.

Earlier studies, based almost entirely on North American dinosaur records, suggested a drop in dinosaur diversity in the 10 million years leading up to their extinction. Fastovsky's conclusions are drawn from his analysis of a new database of global dinosaur records, which shows that much of the diversity of dinosaur genera is found in fossils unearthed in Asia and South America.

Fastovsky also believes that searching for more dinosaur fossils -- though there are likely many more to be found -- will shed little new light on this subject. Instead, he said his analysis suggests that "a more useful approach to understanding the dynamics of their evolution would be to more precisely date the ones that we already know about."

A plot of data on mass extinctions. Dinosaurs survived the mass extinction that took place about 200 million years ago. Credit: University of Chicago

Ankylosaurus dinosaur. Image credit: UCarleton

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On the Net:

NASA

University of Rhode Island

Gerta Keller's Chicxulub Debate

Impact Hazards Website

NASA/JPL Near Earth Object Program

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