Dinosaurs were heading for extinction long before the meteor impact that is believed to have wiped them out, new research suggests.
The study, published in the Proceedings of the National Academy of Sciences, says dinosaurs had entered a long-term decline 90 million years ago, with species going extinct faster than new ones emerged. Then, 24 million years later, the catastrophic six-mile-wide asteroid strike occurred off the coast of Mexico.
"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 study co-author Chris Venditti, an evolutionary biologist at the University of Reading.
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Lead researcher Dr Manabu Sakamoto, from the University of Reading, said: "While the asteroid impact is still the prime candidate for the dinosaurs' final disappearance, it is clear that they were already past their prime in an evolutionary sense.
"While a sudden apocalypse may have been the final nail in the coffin, something else had already been preventing dinosaurs from evolving new species as fast as old species were dying out."
That "something else" remains unexplained, says Sky News, but it is possibly linked to the break-up of continental land masses and the sustained volcanic activity of the time.
While dinosaurs overall were seeing a sharp decline, the study did show that "duck-billed dinosaurs and horn-faced dinosaurs appear to have been booming just before the meteor impact occurred", says The Guardian.
It is this discovery that has left some scientists unconvinced by the study's findings, adds the newspaper.
"It may be that the effects of the asteroid were a bit worse because you had dinosaurs that maybe weren't as strong in an evolutionary sense as they once had been," said paleontologist Stephen Brusatte, from the University of Edinburgh. "But I think if there was no asteroid, you would still have dinosaurs around today."
