The dinosaurs, we are now told, were dying out before the asteroid hit.
From Ed Yong at the Atlantic:
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, he 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. (A speciation event occurs when one species diverges into two.)
If anything, Sakomoto’s study, in revealing the dinosaurs’ slow decline, reminds us about just how long they ruled for—a period of 180 million years, during which many species came and went. More.
Sakamoto’s thesis is contested, of course but it has an explanatory advantage: Groups that dominated the planet for that length of time probably wouldn’t be entirely extinguished by one single event. There must have been other factors.
Colin Patterson suspected that about the trilobites as well. There must have been something that was going wrong for them besides the grand Permian die-off.
Lots of dino interest out there just now:
See also: Dino kin grew more like birds than reptiles
Why weren’t there many dinosaur species?
Size helped largest dinos survive longer
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The official story is pretty dramatic: