Scientists Discover Ancient “Swamp Dweller” From the Age of the Dinosaurs in Colorado

Colorado paleontologists found a rare fossil mammal, Heleocola piceanus, from 70-75 million years ago. The discovery shows some ancient mammals were larger than previously thought.

A team of paleontologists near Rangely, Colorado, has discovered a new (or rather, ancient) state resident—a fossilized mammal roughly the size of a muskrat, which likely scurried through swamps during the Age of Dinosaurs.

The researchers, led by the University of Colorado Boulder’s Jaelyn Eberle, published their findings in the journal PLOS ONE.

Eberle and her colleagues named their discovery, which they identified from a piece of jawbone and three molar teeth, Heleocola piceanus. The animal lived in Colorado roughly 70 to 75 million years ago—a time when a vast inland sea covered large portions of the American West. (Fittingly, “Heleocola” roughly translates to “swamp dweller” in Latin).

“Colorado is a great place to find fossils, but mammals from this time period tend to be pretty rare,” said Eberle, curator of fossil vertebrates at the CU Museum of Natural History and professor in the Department of Geological Sciences. “So it’s really neat to see this slice of time preserved in Colorado.”

Compared to much larger dinosaurs living at the time like tyrannosaurs or the horned ancestors of Triceratops, the new fossil addition to Colorado might seem tiny and insignificant. But it was surprisingly large for mammals at the time, Eberle said.