USGS geologist Jeff Pigati flagging potential sample locations at the Snowmastodon site. Photo courtesy of Helen Richardson (Denver Post).
Complete ancient, high-elevation ecosystems are rarely preserved across glaciations. In fact, prior to discover of the Snowmastodon site in the Rocky Mountains of Colorado, no multi-proxy biotic records from the Sangamon Interglacial (125,000-75,000 years before present [yrBP]) were known from elevations greater than 1,000 m in North America. In 2010, construction to enlarge a reservoir at 2,720 m in the Colorado Rockies revealed a series of stacked Sangamonian ecosystems with abundant and exceptionally well-preserved plant, invertebrate, and vertebrate remains. Scientists and volunteers from the Denver Museum of Nature & Science recovered more than 5000 bones in two short field seasons ending in July 2011. The fossils included at least seven large mammals: American mastodon, the giant Bison latifrons, Jefferson's ground sloth, Columbian mammoth, ice-age deer, horse, and camel, as well as a number of smaller animalsórodents, salamanders, reptiles, snakes, fish, and birds. In addition to the vertebrate fossils, the site is host to exceptionally well-preserved plant, insect and aquatic invertebrate fossils ó beetle parts are iridescent, plants are still green, and conifer cones are intact. The Snowmastodon site provides an unparalleled long-term record of biodiversity and climate change in the high-elevation Rocky Mountains.
Why is this research important?
Analysis of pollen and plant macrofossils show major vegetation changes occurred here several times between ~130,000 and 50,000 yrBP, a period that includes the Sangamon Interglacial period. Climate conditions during Sangamonian times are closely analogous to projected future conditions for the region. Understanding how these fragile, high-elevation ecosystems responded to climate change in the past allows us to better prepare for the future.
Project Team: Tom Ager, Bruce Bryant, Paul Carrara, Jeff Honke, Shannon Mahan, Dan Muhs, Jim Paces, Eugene Schweig (all USGS), plus 30 others from the Denver Museum of Nature and Science and academic institutions in the U.S., Canada, Europe, and Puerto Rico.