English: Mammut americanum (Kerr, 1792) - American mastodon partial humerus from the Pleistocene of Colorado, USA. (DMNH specimen, Denver Museum of Nature & Science, Denver, Colorado, USA)

Colorado's Snowmass fossil site was discovered in 2010 and has become one of the most significant and richly fossiliferous Pleistocene locality in the world. The first fossil was noticed during bulldozer excavation at Ziegler Reservoir in the town of Snowmass Village. Tens of thousands of individual fossils have been recovered. The most common species of vertebrate is the tiger salamander, Amystoma tigrinum. The most common species of mammal is the American mastodon, Mammut americanum. The bone shown above is an example.

The Snowmass fossil site occurs in a long-lived Pleistocene-aged, high-altitude glacial lake deposit in Colorado's Elk Mountains. It is located near the intersection of Snowmass Creek Valley and Brush Creek Valley (= tributary). During the Pleistocene Ice Age, the Snowmass Creek Valley was filled with an alpine glacier. After the Bull Lake glaciation receded from the Elk Mountains about 155,000 to 130,000 years ago, a then-new moraine deposit blocked drainage from Brush Creek and formed a ~10 meter-deep glacial lake. The lake eventually filled up with fine-grained siliciclastic sediments, interbedded with some coarse-grained, poorly-sorted intervals near the lake margin. The latter units likely represent landslide deposits and subaqueous mass wasting events.

Fossil-hosting lacustrine sediments have been dated by various methods to between ~140,000 years ago and over 45,000 years ago.

The partial mastodon humerus bone shown above is remarkable for having tooth marks made by a short-faced bear (Arctodus simus) and teeth scrape marks made by rodents.

Classification: Animalia, Chordata, Vertebrata, Mammalia, Proboscidea, Mammutidae

Locality: Snowmastodon site, Ziegler Reservoir, Snowmass Village, central Pitkin County, western Colorado, USA

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Site-specific info. mostly synthesized from:

Pigati et al. (2014) - Geologic setting and stratigraphy of the Ziegler Reservoir fossil site, Snowmass Village, Colorado. Quaternary Research 82: 477-489.

Mahan et al. (2014) - A geochronologic framework for the Ziegler Reservoir fossil site, Snowmass Village, Colorado. Quaternary Research 82: 490-503.

Sertich et al. (2014) - High-elevation Late Pleistocene (MIS 6-5) vertebrate faunas from the Ziegler Reservoir fossil site, Snowmass Village, Colorado. Quaternary Research 82: 504-517.

Fisher et al. (2014) - Taxonomic overview and tusk growth analyses of Ziegler Reservroi proboscideans. Quaternary Research 82: 518-532.

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See info. at: en.wikipedia.org/wiki/Mastodon and

en.wikipedia.org/wiki/Snowmastodon_site