That finding cemented that fast rates of anatomical change don’t need to coincide with genetic diversity or an abundance of species (called taxonomic diversity), and further rebutted adaptive radiation as the only explanation for the origin of new animal groups and body plans. The researchers also note that it took reptiles almost 10 million years to recover to previous levels of anatomical diversity.

“That kind of tells you on the broad scheme of things and on a global scale how much impact, throughout the history of life, sudden environmental changes may have,” Simões said.

Further evidence that contradicted adaptive radiation included similar but surprising findings on the origins of snakes, which achieved the major aspects of their skinny, elongated body plans early in their evolution about 170 million years ago (but didn’t fully lose their limbs for another 105 million years). They also underwent rapid changes to their skulls about 170 to 165 million years ago that led to such powerful and flexible mouths that today they can swallow whole prey many times their size. But while snakes experienced the fastest rates of anatomical change in the history of reptile evolution, these changes did not coincide with increases in taxonomic diversity or high rates of molecular evolution as predicted by adaptive radiations, the researchers said.

The scientists weren’t able to pinpoint why this mismatch happens, and suggested more research is needed. In particular they want to understand how body plans evolve and how changes in DNA relate to it.

“We can see better now what are the big changes in the history of life and especially in the history of reptile life on Earth,” Simões said. “We will keep digging.”

This work was supported by an Alexander Agassiz Postdoctoral Fellowship from the Harvard Museum of Comparative Zoology and by the National Science and Engineering Research Council of Canada.