19 December 2015

19. Snowmass

Bison latifrons skull at Snowmass
Denver Museum of Nature & Science
Location: Colorado, USA
Age: Pleistocene (140,000-55,000 years ago)

While diprotodonts and kangaroos were getting trapped in the caves of Naracoorte, an entirely different group of megafauna existed in North America.  Perhaps our best window into what this fauna looked like before the arrival of humans is provided, unusually, by a high-elevation site west of Denver.  Skiers are likely familiar with Snowmass, one of the many resort towns that dot the Colorado Rockies, but since 2010 it has become a familiar place to paleontologists as well.  While expanding a reservoir in town, a bulldozer operator uncovered the remains of a much older, natural body of water: a lake that had entombed the remains of numerous Pleistocene organisms.  The nickname of the site, Snowmastodon, is due to the large numbers of American mastodon (Mammut americanum) found there.  Also present are other mainstays of the continent's megafauna, notably the mastodonts' distant relative the Columbian mammoth (Mammuthus columbi), the ground sloth Megalonyx jeffersoni, the long-horned Bison latifrons, as well as camels, horses, and deer.  Snowmass is more than just a megafaunal bone bed, though: also recovered from the site have been small animals such as reptiles, amphibians, rodents, and fish, as well as plant and pollen fossils.  These last have been especially important in reconstructing environmental responses to climate change through time and are a nice illustration of how variable the response of ecosystems to change can be; during one cooling event, for example, Snowmass seems to have stayed relatively warm, while during another its decrease in temperature was greater than the global average.  Unusual among North American megafauna sites, the Snowmastodon fossils were deposited entirely prior to the arrival of humans to the continent, making it an ideal study site for those interested in the changes to an ecosystem brought about by climate and other natural factors.

Visit: The town of Snowmass operates an Ice Age Discovery Center focusing on the site.
Fossils: The Denver Museum of Nature & Science, an excellent museum and a long-time personal favorite, is the repository for all Snowmass material.
Is there a relevant book full of gorgeous fossil photos that I can gift to a paleontologically-minded friend?: Not for adults, but Kirk Johnson, one of our greatest paleontological ambassadors, has written a book about the site for kids.

This post is part of my 2015 Paleontology Advent Calendar, a series of vignettes on lagerstätten - sites of exceptional fossil preservation - that document changes in climate and environments through the Cenozoic.  You can see the other posts here.

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