A team of paleontologists has discovered a fossil in northwest Colorado, revealing a new species of mammal that lived alongside dinosaurs.

CU Boulder professor Jaelyn Eberle and colleagues discovered a muskrat-like mammal that lived in Colorado about 70 to 75 million years ago. It was discovered near Rangely and named Heleocola piceanus. The team’s findings were published on October 23.

Although the animal probably weighed two pounds, it is considered large for a mammal at this time and relatively rare.

“It’s a little bit bigger than the mammals that were scurrying around at that time,” Eberle said.

John Foster, a scientist at the Utah Field House National Park Museum of Natural History, remembers first seeing the mammal’s jaw, protruding from a slab of sandstone in 2016. The fossil measured about an inch in width. long.

“I said, ‘Gosh, this is huge,’” Foster said in a statement.

The muskrat was likely a plant omnivore, meaning it fed primarily on plants with a few insects or other animals. Eberle said that for now, the mammal appears to be found only in Colorado.

“It’s great to see it in the news and to see a whole new genus of fossil mammal emerging from western Colorado,” she said.

The Colorado in which the mammal lived 70 million years ago would be unrecognizable today. At that time, it was a swampy, swampy land home to turtles, dinosaurs and crocodiles.

“The area might have looked a bit like Louisiana,” ReBecca Hunt-Foster, a paleontologist at Dinosaur National Monument in Utah and western Colorado, said in a statement. “We see a lot of animals that lived happily in the water, like sharks, rays and guitarfish.”

However, most mammals were the size of a mouse or rat. Examining the new mammal’s teeth, Eberle said they resembled the mouth of an opossum.

Scientists have less information about when the newly discovered mammal lived. This is due to a sea wave that covered many areas of western North America, meaning there is less land sediment containing fossils. This discovery constitutes a new step in the understanding of this period.

“Because we haven’t represented this time slice, this 70 to 75 million year old time slice, it’s just not as well known as other late Cretaceous slices,” said Eberle.

She said scientists are learning more about mammal diversity during this period than was known about 20 years ago. She said it’s exciting and cool that Colorado plays a role in it.

“It’s important to know if we’re going to understand the evolution of mammals, and we’re mammals, so we need to go back… to understand the roots of the types of mammals that we live with today,” said Eberle.