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Around 66 million years ago, the sky fell on the dinosaurs’ heads. An asteroid smashed into the Yucatan Peninsula, causing cataclysmic climate changes that marked the end of the Cretaceous period, and killed off some three-quarters of animal species. A small proportion of hardy birds survived, but the other dinosaurs went extinct.
They were, however, already in decline.
Manabu Sakamoto from the University of Reading has shown that dinosaur species were going extinct faster than new ones were appearing, for at least 40 million years before the end of the Cretaceous. The dinosaur opera had already been going through a long diminuendo well before the asteroid ushered in its final coda.
Many other researchers had looked at the fates of the dinosaurs before that infamous extinction event and suggested that they were already declining. But most of these studies had simply tabulated raw numbers of species from different blocks of time. This approach has problems: the rocks from certain time periods may simply be better at preserving fossils, or may have been more intensively scrutinized by fossil-hunters.
Together with Michael Benton and Chris Venditti, Sakamoto took a recently published family tree, comprising 614 dinosaur species, and modeled the rates at which new species arose and old ones went extinct. “We’re not counting numbers of species throughout the history of dinosaurs, but of speciation events,” he explains.
Read full, original post: The Long Decline of the Dinosaurs
