Palaeontologists have uncovered an extraordinary piece of the past hidden in the windswept hills of western Colorado – a fossilised mammal, about the weight of a chicken, that once scurried through prehistoric swamps around the time of the dinosaurs.
This ancient creature, now named Heleocola piceanus (H. piceanus), offers a glimpse into what life was like in the US state some 70 to 75 million years ago.
The fossil, discovered by a team led by Jaelyn Eberle from the University of Colorado Boulder, was identified from a small fragment of jawbone and three molar teeth.
It was uncovered near the towns of Rangely and Dinosaur, close to the Dinosaur National Monument. According to Eberle, the name Heleocola fittingly translates to 'swamp dweller' in Latin, as the mammal lived in a region where a vast inland sea once spread across the American West.
“Colorado is a great place to find fossils, but mammals from this time period tend to be pretty rare,” says 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.”
Though it may seem small compared to the colossal dinosaurs such as tyrannosaurs that roamed the region, H. piceanus was actually a giant by mammalian standards during the Late Cretaceous.
Weighing an estimated two pounds or more, it was much larger than the typical mouse-sized mammals of the time. Based on its teeth, the creature likely had a plant-based diet, with perhaps a few insects or other small critters added to the mix.
The discovery highlights the richness of western Colorado’s fossil beds, long overlooked in favour of their larger dinosaur counterparts.
“It’s a small town, but, in my experience as a palaeontologist, a lot of cool things come out of rural environments,” Eberle says. “It’s nice to see western Colorado have an exciting discovery.”
The fossil also provides a fascinating snapshot of a prehistoric Colorado that is unrecognisable to us today. Palaeontologists John Foster and ReBecca Hunt-Foster, co-authors of the study, have been digging in this region for over 15 years. They describe a landscape that once resembled the marshes and estuaries of modern-day Louisiana, where turtles, duck-billed dinosaurs, and even giant crocodiles thrived alongside creatures such as sharks and rays.
John Foster remembers spotting the jawbone of H. piceanus protruding from a slab of sandstone in 2016. The fossil measured about an inch long. “I said, ‘Holy cow, that’s huge."
The discovery of larger mammals like H. piceanus reveals that some species were much bigger than previously thought, adding a new dimension to our understanding of mammalian life during the Age of Dinosaurs.
Find out more about the study Paleontologists discover Colorado ‘swamp dweller’ that lived alongside dinosaurs
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