Quantitative analysis of molar shape may provide a metric for paleontological phylogeography or the study of intraspecific relationships in the fossil record. In this study, outlines of the lower 3rd molars (m3) of North American Marmota were analyzed as between-shape distances after ordination with eigenshape analysis. Based on comparisons with cytochrome b, quantitative divergence in molar shape appears to be a reasonable proxy for phylogenetic reconstruction at the level of populations, subspecies, and the most closely related species of marmots. Phylogeographic analysis of living North American marmots and middle Pleistocene fossils from Porcupine Cave, Colorado, revealed that the latter were more closely related to extant Marmota monax than they are to M. flaviventris, which currently inhabits the Porcupine Cave area, suggesting that the origin of living species occurred in regions different from those they inhabit today. Change in molar shape was significant from level to level through the Porcupine Cave section, which spans a glacial–interglacial cycle, but was not correlated with environmental change. The amount of morphological difference among conspecific populations of living M. monax suggested that they differentiated over many glacial cycles, whereas morphological differences between M. caligata and M. flaviventris were smaller and may have evolved over fewer cycles.
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