Ancient Sloths and Mastodons Turn Up in Colorado

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The ancient world has poked its way to the surface in Colorado.

Scientists excavating what they call "an ice-age ecosystem" in the resort town of Snowmass Village, CO, say they have found the first Jefferson's ground sloth ever discovered in Colorado -- a companion to the mammoths and mastodon bones already turned up at the remarkable site.

Denver Museum of Nature & Science research associate Greg McDonald confirmed Saturday that a bone found earlier this week is the upper arm of the Jefferson's ground sloth. He said that other sloths have been found in Colorado, but they were a different species called Harlan's ground sloth. He and his colleagues were ecstatic about the range of bones found at the site.

“I’m trying to think of a cooler fossil that I’ve ever seen in my life,” said Dr. Kirk Johnson, the Museum’s chief curator and vice president of Research and Collections. “This is the iconic fossil recovered thus far in the excavation.”

So far, scientists working at the site have also found a Columbian mammoth, American mastodon, ice-age bison and an ice-age deer. When combined with the well-preserved plant matter, insects, and invertebrates found at the site, the excavation is revealing an exceptionally-well preserved ecosystem.

“It is truly uncommon to get all parts of a fossil ecosystem preserved in one place,” said Dr. Ian Miller, the Museum’s curator of paleontology and chair of the Earth Science Department. “It’s one of the most exciting scientific discoveries I’ve ever worked on.”

The skull and horns of a bison were discovered at the bottom of a reservoir site. When both horns were repositioned with the skull, the span of the horns was greater than six feet. The size of the skull and horns indicates the ice-age animal was twice as large as modern bison: The entire specimen weighs 250 pounds.

Several renowned scientific experts arrived at the dig site to advise and consult with the Museum’s scientific staff. Experts are debating the age and identification of the bison specimen. Similar species found elsewhere in the western United States have indicated these extremely large bison are often found in sediments as old as 30,000 to 50,000 years old.

If confirmed, this suggests that the Snowmass Village site contains fossils from a range of ages, not just a single age. If true, this would greatly increase the scientific significance of the site, according to Johnson.