SCIENTISTS have helped uncover a new species of ancient mammal that lived during the time of the dinosaurs.

The small, furry creature, dubbed the 'primeval beaver', resembled a rodent and would have been active at the time tyrannosaurus rex and its relatives roamed the earth.

The species even survived the event which brought about the extinction of the dinosaurs, but later died out when it was replaced by the mammals which gave rise to today's rodents.

Scientists say it is unclear why the animals - known as multituberculates - were superseded, but it may be because modern rodents were smarter, grew more quickly, or reproduced faster, giving them an edge in competing for resources.

The new species, known as Kimbetopsalis simmonsae, was discovered during a dig in New Mexico by a team from Edinburgh University, the New Mexico Museum of Natural History and Science and the University of Nebraska.

Uncovering the creature has helped scientists update the mammals' family tree and their research revealed that the new fossil dates to about 500,000 years after the event that wiped out the dinosaurs, which is thought to have been a meteorite or comet striking the earth.

The fossil remains are thought to have been from a forebear of the biggest species in the group, which weighed up to 220lb (100kg) and might have resembled a large beaver.

The mammals originated some 100 million years before the dinosaurs were killed off and had strange and complex teeth with sharp incisors and molars with lots of cusps that were suited to their diet of plants and leaves. Studying the creatures may aid understanding of other mass extinctions, scientists said.

Dr Steve Brusatte of Edinburgh University's School of GeoSciences, who took part in the research, said: "We could think of Kimbetopsalis as a primeval beaver, which lived only a few hundred thousand years after the asteroid impact that killed the dinosaurs.

"The asteroid caused apocalyptic environmental change, but it seems like mammals began to recover pretty quickly afterwards. It was in this brave new world that our mammalian ancestors got their start."

The study was published in the Zoological Journal of the Linnean Society. It was supported by the Marie Curie Foundation, the Natural Environment Research Council, the US Bureau of Land Management, and the National Science Foundation.

Dr Thomas Williamson of the New Mexico Museum of Natural History and Science, who led the research, added: "Finding this new mammal was a pleasant surprise. It helps fill an important gap in the record of this group of mammals.

"It's interesting that this odd, now extinct group, was among the few to survive the mass extinction and thrive in the aftermath.

"It may be because they were among the few mammals that were already well-suited to eating plants when the extinction came. This new species helps to show just how fast they were evolving to take advantage of conditions in the post-extinction world."