New evidence suggests the diversity of nonavian dinosaur species may have been dropping for 10 million years before they were wiped out by an asteroid 66 million years ago.
A study demonstrates how a cooling climate and the loss of herbivores set off a chain reaction that turned the Cretaceous ecosystem against the creatures. The research was conducted by an international team of scientists, including researchers from the University of Bristol in England and the Institut des Sciences de l'Evolution de Montpellier in France.
For decades, paleontologists have debated whether this was the case. Many believe that the diversity of nonavian dinosaur species was still substantial before they died out. Some scholars even think the dinosaurs were still evolving at the time.
"The alternative scenario is that dinosaur diversity was not that high and was instead lower just before the asteroid impact than millions of years before," study lead author Fabien Condamine said. "Here, the meteorite is seen as a coup de grace for dinosaurs, which would have been declining."
A complex set of variables had previously hampered the attempt to determine the situation of the dinosaurs before the asteroid - including inadequate fossil records, uncertainty about age-dating the fossils and concerns about evolutionary models.
So, with more than 1,600 dinosaur records, the researchers ran each model millions of times to account for all potential causes of inaccuracy. Finally, to determine whether the analyses would converge and point to the most possible consequence.
According to co-author Mike Benton of the University of Bristol, the dinosaur data ultimately led to a handful of causes for the species' demise.
"It became clear that there were two main factors. First, that overall climates were becoming cooler, and this made life harder for the dinosaurs which likely relied on warm temperatures," Benton said.
The study was published in the journal Nature Communication.