By Nicola Davis
Dinosaurs were in decline long before the asteroid struck that spelt their doom, new research suggests.
Dinosaurs were on the up and up from the late Triassic about 220m years ago, with new species arising faster than others went extinct. But the study reveals their fortunes had begun to change long before the catastrophic six-mile-wide asteroid hit what is now the Gulf of Mexico, 66m years ago.
The research, the authors believe, could resolve a longstanding controversy among palaeontologists.
“One of the things that has been long debated about dinosaur evolution is whether they were reigning strong right up until the time of the meteorite impact, or whether there was a slow, gradual decrease in [the emergence of new species] or an increase in extinction before that time,” said Chris Venditti, an evolutionary biologist at the University of Reading and an author of the paper.
Writing in the Proceedings of the National Academy of Sciences, researchers from the University of Bristol and the University of Reading describe how they carried out a new kind of statistical analysis based on large “family trees” of dinosaurs, allowing them to explore the rise and fall of species as time marched on. The study looked at the three major groups of dinosaur: the ornithischians (beaked herbivores such as Stegosaurus), theropods (flesh-eating beasts such as Tyrannosaurus rex) and sauropods (long-necked plant-eaters that included Diplodocus).
The results showed that while dinosaurs flourished from about 220m years ago, with species arising faster than they went extinct, about 140m years ago their success started to stall. Eventually, about 90m years ago, 24m years before the asteroid hit, the dinosaurs entered a long-term decline, with species going extinct faster than new ones emerged.
That, the authors reveal, could have left the dinosaurs more vulnerable to extinction when the six-mile-wide disaster struck. “Because diversity was lacking, because species were going extinct and not being replaced, it might have made them more susceptible,” said Venditti.
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