DESCRIPTIONS OF INTERGLACIAL MAMMUT (MAMMALIA, PROBOSCIDEA) FROM SNOWMASS, COLORADO

Over 4000 fossils of mastodons were recovered in 2014 from the Ziegler Reservoir, in Snowmass, Colorado. Ziegler Reservoir fossil bearing deposits were dated between 140,000 to 45,000 years ago based on four independent chronometric techniques. The site has an elevation of ~2705 meters above sea level, making it one of the few paleontological sites that represents an alpine ecosystem dated to Marine Isotope Stage (MIS) 5 in North America. Previous assessments of the Ziegler Reservoir fossil site (ZRFS) mastodons based on M3/m3 L:W ratios, and the presence of mandibular tusks, led researchers to conclude they are Mammut americanum, not Mammut pacificus. This study formally describes the cheek teeth, mandibles, crania, and femora of the ZRFS mastodons. Various statistical methods including descriptive statistics, analysis of variance (ANOVA), post hoc tests, and discriminant analysis identify the ZRFS mastodons as Mammut americanum, which is significantly different from Mammut pacificus. In addition, ZRFS mastodon molars fall within the expected linear measurements for Mammut americanum and are morphologically fairly typical for the genus. The mandibles display a well-developed, “spout-like” symphysis with large alveoli for mandibular tusks. Body mass estimates of the mastodons were calculated from femora measurements, and age of the individuals was determined through dental wear patterns. A niche model was developed from last interglacial period bioclimatic variables and North American localities dating to MIS 5 which contained remains of Mammut. Incorporating measurements from the ZRFS mastodons into large comparative datasets will contribute to ongoing research into the phylogenetic and biogeographic structure of Late Pleistocene Mammut.