A SPECIES LEVEL TAXONOMIC ASSESSMENT OF MAMMOTH MOLARS FROM THE CENTRAL GREAT PLAINS, USA

Fossilized mammoth (Mammuthus) teeth are relatively durable in comparison to skeletal material and are thus often discovered in isolation. A reliable means of identifying mammoth species from teeth is essential for accurately establishing their biogeographic ranges. The two most widely used characters for identifying mammoth molars are lamellar frequency (LF), measured as the number of plates per decimeter, and the thickness of exposed enamel ridges (ET) on the occlusal tooth surface. Woolly mammoths (M. primigenius) generally possess relatively thin enamel plates (ET=1.0-2.0 mm) and high lamellar frequency counts (LF=7-12). Conversely, Columbian mammoths (M. columbi) typically have thick enamel plates (ET=1.5-3.0 mm) and low lamellar frequency counts (LF= 5-9).

We measured 133 mammoth molars within University of Nebraska State Museum (UNSM) collections for enamel thickness and lamellar frequency. The specimens were collected from various localities throughout Nebraska and the Nishnabotna River region of Iowa and Missouri. Only those falling outside of the overlapping range of character values between both taxa were assigned to a species on the basis of our results. Potential effects of tooth wear on the measurements were taken into account by estimating wear stages in our specimens from those of the African elephant (Loxodonta africana). We used a Spearman's rank correlation (SRC) to determine the relationship between wear stages and both dental characteristics to test if wear posed a significant impact on the measured dental parameters. The SRC tests yielded a weak, insignificant correlation between the dental measurements and tooth wear, suggesting that wear poses a negligible effect on our taxonomic assessments.

Of the 133 UNSM mammoth molars measured, we determined that 24 belong to M. primigenius, and 70 to M. columbi. The specimens collected from Iowa and Missouri consist of both species, with a higher abundance of M. primigenius. Conversely, those collected from Nebraska belong almost exclusively to M. columbi. This distribution may due to the southward extension of the Laurentide ice sheet in north-central Iowa during the Late Pleistocene, providing more suitable habitat for the steppe-adapted woolly mammoth.