The Schreger pattern is a microstructural feature unique to proboscidean dentin. Previous studies have attempted to use characteristics of the Schreger pattern (qualitative descriptions and the angle made by intersecting Schreger lines) to distinguish among proboscidean species, with varying degrees of success. In Columbian mammoths (Mammuthus columbi), for example, the Schreger angle tends to be acute and the pattern resembles a “V,” but in American mastodons (Mammut americanum) the Schreger angle tends to be obtuse and the pattern resembles an “X” or a checkerboard. The aim of this project is to qualitatively and quantitatively describe the Schreger pattern in tusks of Pacific mastodons (Mammut pacificus). The Pacific mastodon, recognized as distinct from its contemporary American mastodon (Mammut americanum) in 2019, is currently known from the Irvingtonian and Rancholabrean of western North America. It is expected that Schreger pattern characteristics are shared between M. pacificus and M. americanum, but no published data supports this hypothesis. The Grizzly Ridge mastodon, housed in the Western Science Center (Hemet, CA), is an Irvingtonian-aged Pacific mastodon discovered near San Francisco, CA. A 3-cm thick transverse cross section of the tusk, with a major diameter of 14.5 cm and a minor diameter of 13.5 cm, was removed for analysis of the Schreger pattern. The section includes the cementum-dentin junction (CDJ) and the pulp cavity. Four thin sections will be made from the transverse section of the tusk at increasing distances from the tusk exterior (CDJ) so that any variation in Schreger pattern from the CDJ to the pulp cavity will be captured. Characteristics of the Schreger pattern will be compared to data from the literature to assess whether there is qualitative or quantitative overlap between Pacific and American mastodons and/or between Pacific mastodons and Columbian mammoths (Mammuthus columbi) to determine if Schreger patterns may be used to distinguish among these contemporary proboscidean species. If little to no overlap exists between Pacific mastodons and Columbian mammoths, then the Schreger pattern may aid in species identification for fossil assemblages containing both species, a common occurrence in the Pleistocene of North America.
