An article published in the journal “Current Biology” describes a research showing that there was a rapid evolution of mammals during the Jurassic period, between 200 and 145 million years ago. That period and in general the Mesozoic era, between 252 and 66 million years ago, were the dinosaurs era so we tended to think that mammals lived in their shadow, in ecological niches, such as nocturnal insectivores. Instead, the discovery of new fossils in recent years showed a series of adaptations with a previously unknown diversification.

Dr. Roger Close led a team that included researchers from the British Oxford University and the Macquarie University in Australia in the first large-scale analysis of the changes in mammals’ teeth and skeletons during the Mesozoic era. This allowed to assess their evolution’s pace, showing that it accelerated during the Jurassic.

In particular, around the mid-Jurassic, the researchers noted a diversification that led to the birth of gliding, digging and swimming mammals. In the Theria subclass – though the taxonomy is different depending on the classification system – which includes almost all mammals that exist today, there was an evolution 13 times faster than the average.

In the multituberculates (multituberculata) (photo ©Jørn H. Hurum and Zofia Kielan-Jaworowska), an order of mammals that got extinct in the Tertiary era, there were radical changes in the skeleton and teeth in the middle of the Jurassic. Towards the end of that period, however, their tendency was towards their typical rodent-shaped bodes. Some people consider them the most successful mammals because this order spread for 100 million years between Asia, Europe and North America.

The reasons for such diversification are unclear. It may have been triggered by environmental changes or perhaps mammals had accumulated some key innovations such as the live birth, hot blood and fur that allowed them to adapt to different ecological niches.

Dr. Close likened this rapid evolution of mammals to the Cambrian explosion, a time when there was the evolution of many species belonging to different phyla. In the Jurassic, an event of that type was confined to mammals but is still very interesting for their spread in various ecological niches.

Mammals’ evolution pace slowed down towards the end of the Jurassic, when they reached a high degree of diversification. Mammals started being dominant only after the dinosaurs extinction but it’s possible that the foundations of that domain were laid with their explosion in the Jurassic.