LONG IN THE TOOTH: TUSK MORPHOLOGY OF LATE PLEISTOCENE PROBOSCIDEANS FROM THE DIAMOND VALLEY LAKE LOCAL FAUNA, INLAND SOUTHERN CALIFORNIA

The Diamond Valley Lake local fauna (DVLLF) of inland southern California is one of the largest Late Pleistocene fossil assemblages in the southwest, producing over 3,000 megafauna specimens identifiable to the genus level. Fossils in this assemblage are likely an unbiased sample of the local population, and have been dated at between ~40,000 and ~13,000 years before present. Proboscideans, both American mastodons (Mammut americanum) and Columbian mammoths (Mammuthus columbi), represent a substantial component (~25 %) of the DVLLF assemblage. The proboscidean material includes at least 15 tusks attributed to mastodons, 6 attributed to mammoths, and 20 of uncertain affinity. Despite the abundance of megafauna recovered in the assemblage, it is often overshadowed by the nearby La Brea Tar Pits, and little work on the DVLLF proboscideans has been published. Previous studies have suggested that western mastodons were smaller and had more narrow molars than eastern mastodons. A recent study showed that the DVLLF mastodons do in fact exhibit subtle differences in molar morphology from eastern mastodon populations, prompting the question: what about the tusks? The goal of this study is to conduct a morphological description of the DVLLF mastodon tusks in order to continue exploring skeletal proportions that may be unique to western mastodons. In addition, all proboscidean tusks from the assemblage will be described in order to document the demography of the DVLLF proboscideans and test the hypothesis that the assemblage represents an unbiased sample of the population. Measurements collected from each tusk, when possible, are total length, maximum tusk circumference, pulp cavity depth, alveolar depth, and maximum tusk circumference. Initial morphological analysis of DVLLF proboscidean tusks indicates an approximately 8:1 ratio of males to females, with the majority of these tusks belonging to adults. Future and ongoing studies on these tusks include growth rate and serial stable isotope analysis (δ¹⁸O, δ¹³C, δ¹⁵N), which will provide data on season of death, diet, and nutritional status for the DVLLF proboscideans.