Jurassic Mammals Evolved 10 Times Faster as They 'Experimented' with New Structures

The Jurassic period wasn't only an age for dinosaurs; it was also an age for mammals. Scientists have found that mammals evolved ten times faster in the middle of the Jurassic than they were at the end of the period.

Early mammals lived alongside the dinosaurs during the Mesozoic era, which occurred from 252 to 66 million years ago. In the past, scientists thought that these mammals were exclusively small, nocturnal insect-eaters. New fossils, though, have shown that they actually developed diverse adaptations for feeding and locomotion, including gliding, digging and swimming.

In order to find out how rapidly the new body shapes emerged, researchers analyzed skeletal and dental changes in Mesozoic mammals. By calculating evolutionary rates across the entire Mesozoic, the scientists revealed that mammals underwent a rapid burst of evolutionary change that reached its peak about 200 to 145 million years ago.

"What our study suggests is that mammal 'experimentation' with different body plans and tooth types peaked in the mid-Jurassic," said Roger Close, lead author of the new study, in a news release. "This period of radical change produced characteristic body shapes that remained recognizable for tens of millions of years."

The researchers actually found that during the mid-Jurassic, mammals were evolving almost ten times faster than they were at the end of the period. This was exemplified by therian mammals, which is the lineage that led to placental mammals and marsupials. This group evolved about 13 times faster than average.

The researchers still aren't sure what caused this evolutionary burst. It could be due to environmental change or perhaps that mammals required a "critical mass" of key innovations that allowed them to thrive in different habitats.

The findings are published in the journal Current Biology.

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