An ancient “swamp-dweller” mammal has been discovered in Colorado.

BOULDER, CO – Paleontologists announced the discovery of an ancient mammal that lived approximately 70-75 million years ago in a swampy area of ​​what is now the Northwest Colorado.

In a study published this week, scientists identified the animal as Heleocola piceanus, a creature about the size of a muskrat that lived when dinosaurs roamed the Earth.

The name is inspired by the environment in which the creature lived. Unlike the Colorado we know today, the Colorado at the time of H. piceanus was partially underwater.

Artistic depiction of H. piceanus in a Late Cretaceous swamp. (Illustrations: Brian Engh-LivingRelicProductions.com, courtesy of Utah Field House of Natural History)

(Brian Engh/FOX Weather)

“The region may have looked a bit like Louisiana,” said ReBecca Hunt-Foster, study co-author and paleontologist at Dinosaur National Monument in Utah and western Colorado. “We see a lot animals that lived quite happily in the water, like sharks, rays and guitarfish.”

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According to the University of Colorado, the newly identified mammal’s name roughly means “swamp-dweller” in Latin due to its swampy environment.

A map of the body of water known as the Western Interior Seaway, covering most of North America, about 75 million years ago.

(Sampson et al., 2010, PLOS ONE / FOX Weather)

At 2 pounds or more, H. piceanus would have been large compared to other mammals of its time, according to lead author and professor in the Department of Geological Sciences Jaelyn Eberle. She noted that the animal is a cousin of modern marsupials.

Eberle and her team made their discovery by analyzing fossils found in the Williams Fork Formation in Rangely, Colorado, in the mid-to-late 1980s, as well as fossils found in the same area in the 2000s.

3D scans of the fossilized jaw bone of the mammal H. piceanus.

(Eberle et al., 2024, PLOS ONE / FOX Weather)

The earlier fossils were originally thought to belong to other ancient mammal species, Aquiladelphis incus and Glasbius piceanus.

However, further research, along with analysis of fossils discovered in 2018, challenged this classification and led scientists to conclude that they had identified a new species of ancient mammal in Colorado.

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“Colorado is a great place to find fossils, but mammals from this period are quite rare,” Eberle said. “So it’s really nice to see this piece of time preserved in Colorado.”