Colorado, United States

A new fossil mammal, nearly the size of a muskrat, was found by a team of palaeontologists when they were scurrying through swamps during the Age of Dinosaurs.

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The researchers, headed by the University of Colorado Boulder's Jaelyn Eberle, published the findings in the journal PLOS ONE on October 23. 

The discovery was identified from a piece of jawbone and three molar teeth by Eberle and her colleagues and was named Heleocola piceanus. 

According to the researchers, the animal existed in Colorado roughly 70 to 75 million years ago and in those times, large portions of the American West were covered by a vast inland sea. 

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"Colorado is a great place to find fossils, but mammals from this time period tend to be pretty rare," said Eberle, who is the 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," he added. 

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New fossil comparatively large for mammals: Researchers

In comparison to larger dinosaurs like the horned ancestors of Triceratops or tyrannosaurs, the new fossil found in Colorado was tiny and insignificant. Eberle said that it was comparatively large for mammals at the time. 

Eberle further expressed her happiness that the town of Rangely, which was near Dinosaur National Monument, is getting its due.

"It's a small town, but, in my experience as a palaeontologist, a lot of cool things come out of rural environments. It's nice to see western Colorado have an exciting discovery," Eberle said. 

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For nearly 15 years, palaeontologists and co-authors of the new study John Foster and ReBecca Hunt-Foster have been visiting this part of the state to dig up fossils every summer. 

"The region might have looked kind of like Louisiana," explained ReBecca Hunt-Foster, who is a palaeontologist at Dinosaur National Monument in Utah and western Colorado. "We see a lot of animals that were living in the water quite happily like sharks, rays and guitarfish," he added. 

John Foster recalled that he first saw a bit of mammal jaw hidden beneath a slab of sandstone which he had found from the site in 2016. The measurement of the fossil was about an inch long.

"I said, 'Holy cow, that's huge,'" stated Foster, who is a scientist at the Utah Field House of Natural History State Park Museum in Vernal, Utah.

(With inputs from agencies)