Dinosaurs were already past their prime when a huge asteroid finished them off 66 million years ago, according to Universities of Reading and Bristol researchers who say their work "changes our understanding of the fate of these mighty creatures." They write in the Proceedings of the National Academy of Sciences of a decades-long debate: whether the creatures were "reigning strong" or "in a long-term decline" before that "final catastrophic event." They say they have for the first time used a statistical approach that allowed them to model the "the evolutionary dynamics of speciation." What they've found is that dinosaur species were going extinct faster than new ones were emerging for as many as 53 million years before the devastating impact, with other factors—including volcanic activity, the breakup of continents, and even our small, furry, egg-eating mammal ancestors—contributing to a long, slow decline.
"We were not expecting this result," lead researcher Manabu Sakamoto says in a University of Reading press release. "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." Discovery explains that their study is the first on the topic to make use of phylogenetic data, "meaning how species are related to one another." And Discovery sees a modern-day lesson in the results: that any group of animals on the evolutionary decline could be eradicated from Earth in the event of another such catastrophe. (Other researchers argue that the asteroid impact was "bad timing" and dinosaurs would still be around today if the asteroid had hit a few million years earlier or later.)