Morphometric data for Mesodma species discrimination

<p><span>Multituberculates remain one of the more poorly understood mammalian clades. The North American multituberculate record is comprised mostly of isolated teeth and incomplete jaws leading to interpretations of relationships based on limited anatomy. Despite the fragmentary record, the p4 of cimolodontan multituberculates is both common and a source of diagnostic characters in systematic studies. The results of a recent morphometric study on the neoplagiaulacid <em>Mesodma</em> suggest that p4 size may be more useful than shape in diagnosing the various species referred to this genus. We tested this hypothesis by applying two different morphometric methods (2D geometric morphometrics and linear measurements) to two samples – (1) one including the p4s of four known species (<em>M. ambigua</em>, <em>M. thompsoni</em>, <em>M. formosa</em>, and <em>M. pygmaea</em>), and (2) a sample of unidentified p4s of <em>Mesodma</em> from the Bug Creek Anthills locality of Northeastern Montana. Our results indicate that while form explains most of the morphological variation in p4s of the various species of <em>Mesodma</em>, linear measurement data support differences in p4 morphology that are not recovered by form data alone. Depending on the methods used, we found evidence for the presence of one or more species of <em>Mesodma</em>in the Bug Creek Anthills fauna. Although shape and size both contribute to morphological variation in the p4 of <em>Mesodma</em>, our results suggest that the diagnostic power of each in isolation, or in combination, varies significantly with the type of methodology employed. </span></p>