Dinosaur extinction occurred at diversity peak
ACCORDING TO a new analysis of global fossil records by a team of researchers led by a University of Rhode Island palaeontologist, 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.
``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, University of Rhode Island professor of geosciences.
Cretaceous period
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.
``Dinosaur diversity was increasing logarithmically throughout their 160 million years on Earth,'' said Fastovsky. ``Their increasing diversity seems to have been fuelled 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.
However, during the late Cretaceous period they became much more specialized in their feeding and behaviour patterns, driving their evolution into more and more genera. The diversity of plant-eating dinosaurs in the Cretaceous was found to be especially high.
Key driving force
``The ability to colonise heretofore unavailable ecospace by the invention of new feeding mechanisms and behaviours 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 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.''
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