侏罗纪中期哺乳动物的进化速度最快

Mammals were evolving up to ten times faster in the middle of the Jurassic than they were at the end of the period, coinciding with an explosion of new adaptations, new research shows. Early mammals lived alongside the dinosaurs during the Mesozoic era (252-66 million years ago). They were once thought to be exclusively small nocturnal insect-eaters, but fossil discoveries of the past decade - particularly from China and South America - have shown that they developed diverse adaptations for feeding and locomotion, including gliding, digging, and swimming.

To find out when and how rapidly these new body shapes emerged a team led by Oxford University researchers did the first large-scale analysis of skeletal and dental changes in Mesozoic mammals. By calculating evolutionary rates across the entire Mesozoic, they show that mammals underwent a rapid 'burst' of evolutionary change that reached its peak around the middle of the Jurassic (200-145 million years ago). 

The team comprised researchers from Oxford University in the UK and Macquarie University in Australia. A report of the research is published in Current Biology.

'What our study suggests is that mammal 'experimentation' with different body-plans and tooth types peaked in the mid-Jurassic,' said Dr Roger Close of Oxford University's Department of Earth Sciences, lead author of the report. 'This period of radical change produced characteristic body shapes that remained recognisable for tens of millions of years.'