The beaver was part of a group of mammals that flourished a few hundred thousand years after the apocalypse that wiped out the dinosaurs, and laid the foundation for the mammals of today.

A fossil discovered in New Mexico has provided scientists with insight into the kinds of mammals that filled the gap left by the dinosaurs when they became extinct 65 million years ago.

"Our new mammal, called Kimbetopsalis simmonsae, would have looked like a prehistoric version of a beaver," explained Stephen Brusatte, a member of the group of scientists that studied the fossil.

"It was a couple of feet long, weighed 10-40 kilograms, and had buck-toothed incisors at the front of its snout that it used to cut up leaves and branches."

The beaver-like creature was the largest known member of a completely extinct group of mammals called multituberculates, which originated alongside the dinosaurs and survived their extinction. In turn, Kimbetopsalis went extinct 35 million years ago when they were superseded by smarter, faster-growing modern rodents.

© REUTERS / Tom Williamson/Handout via Reuters The teeth of Kimbetopsalis simmonsae

The fossil of Kimbetopsalis was found in New Mexico, and the scientists believe that the creature was one of many that flourished in the period immediately after the asteroid impact that wiped out the dinosaurs.

Kimbetopsalis had a herbivorous diet, in contrast to the mammals which went before them, and possessed highly complex cheek teeth adapted for eating plants, according to the study, published in the Zoological Journal of the Linnean Society.

The beaver was larger than the primitive mammals that had lived alongside the dinosaurs over the previous 150 million years, which rarely, if ever, got above 10-15 kilograms in mass.

"Kimbetopsalis is testament to how the history of life hinges on moments that can reset the course of evolution," writes Brusatte.

"Mammals were clearly prospering in this brave new world, getting their first taste of evolutionary success and laying the foundation for a whole new era in which they, not dinosaurs, reigned supreme. This burst of evolution led to primates, which eventually led to us."