BOULDER, Colo. (CBS4) - Scientists at the University of Colorado Boulder say they found three new fossil mammal species. The discovery was made in an ancient river bed in southern Wyoming.

Scientists say the fossils are Conacodon hettingeri, Miniconus jeanninae and Beornus honeyi. They roamed the area within a few hundred thousand years after a mass extinction event 66 million years ago.

They are of ancestors of today's hoofed animals like cows, horses or moose.

"We still don't fully understand what happened after the extinction of the dinosaurs. We don't have anything quite like condylarths living today, so there's a lot of speculation about their biology and ecology," said Jaelyn Eberle, curator of fossil vertebrates at the CU Museum of Natural History and a professor of geological sciences.

Many of the animals were not bigger than an average house cat, and they had toes rather than hooves.

Paleontologists say they may have underestimated how diverse the mountain west was after the extinction of dinosaurs.