Chronological and Paleobiological Controls on the Expression of Mastodon (Proboscidea, Mammutidae) Mandibular Tusks in North America

• Main Authors: Inabinett, Matthew, Widga, Chris
• Published: Digital Commons @ East Tennessee State University 2019
• Subjects: mastodon; statistics; paleontology; Quaternary; proboscidean; Paleobiology; Evolutionary Biology
• Online Access: https://dc.etsu.edu/asrf/2019/schedule/142

Mastodons (family Mammutidae) are widespread and abundant in of Pleistocene faunas across North America, exhibiting considerable variation in morphology over their broad geographic and temporal range. Mandibular tusks are a notably variable feature among mastodons; these tusks vary in size and shape, and many mastodons lack them entirely, or possess only one. Patterns in mandibular tusk distribution could potentially indicate important selective controls on different populations. Various hypotheses have been proposed to explain the distribution of mastodon mandibular tusks, attributing their presence to geographic, temporal, and sexual variation, but there have been no analyses investigating whether there is statistical support for patterns of mandibular tusk distribution. We analyze a dataset of more than 100 mastodons from throughout North America. Mandibles were coded for the presence/absence of mandibular tusks. These data were used to test whether tusk presence was related to geographic or chronological patterns. The most statistically-significant differences were recorded between interglacial- and late glacial-interval mastodons. Interglacial mastodons had mean differences of 0.958 and 0.827 from last glacial maximum and post-last glacial maximum mastodons, respectively, with essentially 0 p-values for both. Though this study is preliminary and uses simple statistical tests, it shows that patterns do exist in the presence of mandibular tusks among mastodons, and that this variability warrants further investigation, particularly with regards to differences in paleoenvironment and paleoecology between interglacial and glacial mastodons that may be responsible for their apparent differences in mandibular tusk presence.