RECIPROCAL ILLUMINATION BETWEEN QUANTITATIVE AND QUALITATIVE CHARACTERS IN UNDERSTANDING THE SYSTEMATICS OF FOSSIL POCKET MICE (RODENTIA: HETEROMYIDAE)

Heteromyid rodents are among the most widespread and abundant vertebrate taxa in North American Neogene faunas. The oldest heteromyid rodents described are from the Oligocene of North America, during the Chadronian North American Land Mammal Age. Extant heteromyids are represented by six genera, all but one of which are found only in North America. The phylogenetic relationships between extant and extinct, and among extinct taxa of heteromyids, are not well known, because fossil heteromyid taxa are represented mainly by isolated teeth. Therefore identification and classification of these rodents are mostly based on dental characteristics. The relatively simple tooth morphology and high variability of various dental characters in heteromyids have hindered identification of new fossils, even to genus or subfamily. Previous studies have generally focused on either qualitative or quantitative dental characteristics in distinguishing heteromyid taxa. Here we conducted both qualitative and quantitative analyses on a select group of heteromyid species whose dentitions have been well described in published literature. A number of the taxa examined co-occur in the microfauna of the Split Rock local fauna in central Wyoming. Differences between qualitative (phylogenetic analysis using parsimony) and quantitative (multivariate cluster analysis) methods revealed biases inherent in using a unilateral approach in the identification of fossil heteromyids and suggest a reason for some of the disagreement about heteromyid systematics. In addition, analyses conducted independently on several genera of heteromyids showed the utility of this combined analytical approach. When applied to higher heteromyid taxa, it is possible to test the conformation of characters of questionably assigned specimens to established generic characters.