WASHINGTON • An asteroid impact in Mexico compounded by colossal volcanism in India 66 million years ago killed about three-quarters of Earth's species, including the dinosaurs.

But soon afterwards, a little animal that looked like a beaver was thriving, exemplifying the resilience of the mammals that would arise from the margins of the animal kingdom to become Earth's dominant land creatures.

Findings published in the Zoological Journal of the Linnean Society yesterday explained the discovery in New Mexico of the fossil remains of Kimbetopsalis simmonsae, a plant-eating, rodent-like mammal boasting buck-toothed incisors like a beaver.

Kimbetopsalis, about 1m long, was likely covered in fur and possessed large molar teeth with rows of cusps used to grind plants. It was one of a group called multituberculates that disappeared about 35 million years ago, after successfully surviving for 120 million years.

It lived in lush forests, rivers, streams and lakes as Earth's ecosystems began recovering from the catastrophe that ended the Cretaceous Period and opened the Paleocene Epoch.

"It shows just how quickly mammals were evolving in that brave new world after the asteroid cleared out the dinosaurs," said palaeontologist Stephen Brusatte of the University of Edinburgh. "Mammals which originated hundreds of millions of years earlier, at the same time as the dinosaurs, now found themselves in an empty world, and they took advantage."

REUTERS