'Prehistoric beaver' find explains how mammals took over world

A team of UK scientists has discovered and classified a previously unknown extinct mammal which flourished as the dinosaurs died out. The beaver-like animal has been named Kimbetopsalis simmonsae.

Dr Stephen Brusatte, of the University of Edinburgh, who led the research, told the BBC the newly found fossil showed how mammals had adapted and survived after an asteroid hit the earth and caused an "extinction event".

He said: "That asteroid hit and suddenly the dinosaurs are wiped out. It looks like mammals were just waiting their turn and as soon as the dinosaurs disappeared, they thrived.

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"Literally, the world changed one day. A whole lot of mammals did die, but this group is one that made it through pretty well."

The significant find was made by a student on Brusatte's team, Carissa Raymond, while prospecting at a site in New Mexico in the US. Brusatte said they realised "pretty quickly" that the fossil was of a previously unseen type of mammal.

Kimbetopsalis would have looked like a "prehistoric version of a beaver", according to Brusatte, writing for The Conversation. It was about two feet in length and weighed between 10kg and 40kg.

The animal was buck-toothed, using the incisors in front of its snout to cut up leaves and branches. Despite appearances though, it was not closely related to the modern beaver.

Instead, Kimbetopsalis was part of a now totally-extinct group of mammals, the multituberculates, which originated at the time of the dinosaurs in the Jurassic and thrived for more than 100 million years.

Kimbetopsalis itself lived for "only" a few hundred thousand years after the asteroid hit – a "blink of the eye" in geological terms, writes Brusatte. It lived in lush forests, rivers and lakes.

Significantly, in the absence of the predating dinosaurs, Kimbetopsalis was much larger than mammals that had come before – and a dedicated plant eater. Few mammals, if any, had been vegetarians before Kimbetopsalis.