72-million-year-old fossil found near Utah leads to discovery of muskrat-sized prehistoric mammal

VERNAL — A previously unknown muskrat-sized mammal species that roamed this region when the Intermountain West looked more like swamps millions of years ago has been discovered by a chance fossil discovery near the Utah-Colorado border.

Paleontologists from the University of Colorado, Utah State Parks Department, Dinosaur National Monument and two other institutions say the mammal, which they named Heleocola piceanus, likely lived in river delta forests that existed in northeastern Utah and the northwest. . Colorado, between 75 million and 70 million years ago.

“Mammals from this time period tend to be very rare, so it’s really cool to see this slice of time preserved in Colorado,” Jaylyn Eberly, a professor of geological sciences at the University of Colorado, said in a statement.

The team’s findings, Published on Wednesday in the magazine PLOS ONEcomes from analysis of fossilized teeth and jaws that were inadvertently collected in 2016 from a sandstone block near Rangeley, Colorado, near Dinosaur National Park and a few miles east of the Utah-Colorado border.

While fragments of the turtle’s shell were visible in the mass, the new mammal discovery was not. It wasn’t discovered until a Western Colorado Museums volunteer noticed a strange collection of fossils while preparing the rock in 2018.

A team of researchers, led by Eberle, began studying what was identified as a jaw fragment with three molars. They were curious because the teeth were roughly five times the size of mammalian teeth typically found in similar blocks of sandstone in an era when most mammals, such as squirrels, were relatively small.

“The jaw, the teeth, everything was much larger than most of the mammalian fossils you see in Cretaceous rocks out there,” said John Foster, curator of collections at the Utah Natural History Field House. “I thought, ‘This is huge.’” State Park Museum, and co-author of the study.

This led to a more comprehensive review of the fossil, which was determined to be 72 million years old.

Eberly identified earlier prehistoric mammals by teeth, which are sometimes all that remains of mammals during this era. The team decided they had found a species that had never been recorded before. They believe it weighed at least 2 pounds and was a cousin to today’s marsupials.

Researchers settled on the name “Heliocula,” or “swamp-dweller,” because it likely lived near rivers and swamp sites spread throughout the world. Western Inland Sea Route and areas east of it, when the region looked more like the modern Mississippi River Delta in Louisiana.

This discovery helps researchers better understand the ecosystem that existed at that time. Foster’s previous work includes all the prehistoric species of fish, dinosaurs, reptiles and mammals that lived in the area at around the same time as Heleukola.

“This delta appears to have been crowded with a wide variety of animals on land and in the water,” he said.