You might say that the dinosaurs were extremely unlucky 65 million years ago. Things were going along swimmingly and then, poof! that nasty asteroid came along and wiped them out.
But before that, apparently, the dinosaurs led a charmed life. A study published in Science suggests the dinosaurs ruled the roost for some 135 million years not so much because they were superior to the competition, but because they were lucky.
Mike Benton of the University of Bristol in England, Stephen L. Brusatte, now at Columbia University, and colleagues studied dinosaurs in relation to a major competing group of reptiles, the crurotarsans, the ancestors of the crocodiles. Both groups survived an extinction about 225 million years ago, but few of the crurotarsans made it through another mass extinction at the end of the Triassic, 200 million years ago.
Scientists had long thought that the reason for this was that the dinosaurs were somehow superior — they were able to outcompete the crurotarsans when the going got tough. But the new study indicates this was not the case.
The researchers developed a database of hundreds of skeletal features of more than 60 dinosaurs and crurotarsans, as well as a new family tree of both groups, and used them to determine evolutionary patterns. They found much more disparity among crurotarsans’ morphological features — a much broader array of shapes and forms.
“The assumption is that the diversity or range of body forms is more or less proportional to the number of modes of life that they’d occupy,” Dr. Benton said. So the finding shows that the crurotarsans were more diverse in terms of their lifestyle, diet and habitat — they filled more ecological niches and were, if anything, the more successful of the two groups in the late Triassic. “The dinosaurs didn’t find a way to squeeze into the crurotarsans’ role,” he said.
But then at the end of the Triassic, for some unknown reason the dinosaurs survived while almost all the crurotarsans did not. “There was a certain amount of luck involved,” Dr. Benton said. “One group got pretty much wiped out and another group soldiered on and took off. The dinosaurs finally got their chance.”