THE dinosaurs dominated life for 135 million years during Earth鈥檚 Jurassic and Cretaceous periods, but only because they got lucky. They were also-rans to their crocodilian cousins until climate change wiped out the competition.
Near the start of the Triassic period, 250 million years ago, the reptilian archosaurs split into the dinosaurs and the crurotarsans, whose only living descendants are the crocodiles. Palaeontologists used to think dinosaurs dominated the last 30 million years of the Triassic, and to do this they must have been better adapted. In fact the two groups are very similar, and many of the 鈥渄inosaur鈥� fossils from that time have turned out to be crurotarsans.
Now there鈥檚 a further challenge to the idea that the dinosaurs had an evolutionary advantage. Steve Brusatte, now at the American Museum of Natural History in New York, and Mike Benton at Bristol University, UK, found that for the 30 million years dinosaurs and crurotarsans coexisted, the two were evolving at essentially the same rate. What鈥檚 more, the crurotarsans had a much wider range of body types than the dinosaurs, so if any group were going to dominate, you would have expected it to be the crurotarsans, says Brusatte (Science, ).
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Yet rapid climate change 200 million years ago wiped out all the crurotarsans 鈥� bar the crocodiles 鈥� while for some reason the dinosaurs sailed through. Brusatte says this shows how evolution does not really record 鈥減rogress鈥� 鈥� the winners may just have luck on their side.
