AGE PROFILE OF TERMINAL PLEISTOCENE COLUMBIAN MAMMOTHS FROM THE TULE SPRINGS FOSSIL BEDS OF SOUTHERN NEVADA

The Tule Springs Fossil Beds are highly fossiliferous Late Pleistocene deposits of the Las Vegas Formation located in northern Las Vegas Valley. The recently established Tule Springs Fossil Beds National Monument protects a large portion of these deposits, but significant fossil sites lie outside the boundaries of the new national monument. One such site, on property owned by Mr. Bill Gilcrease, has produced a large number of Columbian mammoth teeth (Mammuthus columbi). Stratigraphically, the site is located within Unit E1 of the Las Vegas Formation. Radiocarbon dates of teeth from this site indicate an age range of at least five thousand years, from approximately 18 Ka to approximately 13 Ka.

Proboscidean molariform teeth occur in a succession of progressively larger teeth that move horizontally through the animal’s mouth during the animal’s lifetime. If the animal lives long enough, a total of six teeth will be used in each quadrant of the mouth. When an animal dies, the size and wear of the teeth in its mouth at that time can be used to determine the animal’s age. In this study we identified 64 molariform teeth that were either complete or complete enough to determine the age of the animal at death. 42 +/- 5% of the animals were juveniles (12 years old or younger); 36 +/- 5% of the animals were young adults (13 to 24 years old); 19% were mature adults (25 to 36 years old), and 3% were older adults (37 to 48 years old).

The resulting age profile most closely matches a “Type A” profile, which is typical of stable or expanding populations. These results suggest that between the Last Glacial Maximum and 13 Ka, the M. columbi population in Southern Nevada was stable.