Fossil moles from the Gray Fossil Site (Tennessee): Implications for diversification and evolution of North American Talpidae

Abstract

The Gray Fossil Site (GFS), an early Pliocene aged site in northeastern Tennessee, is one of the richest Cenozoic localities in the eastern United States. To date, thousands of micro-vertebrate specimens have been collected, but few small mammals have been identified and thoroughly studied. This study describes the first talpid specimens recovered from the GFS, which represent four talpid species (Parascalops grayensis sp. nov., Neurotrichus sp., Mioscalops sp., and a new stem desman, Magnatalpa fumamons gen. et sp. nov.). The fossil taxa were quantitatively compared to a wide range of extant and extinct moles using a geometric morphometric analysis of humeri shape. Humeral morphology has commonly been used to diagnose talpid species and study their relationships. Quantitative analysis shows humerus shape is highly reflective of locomotor ecology in extant talpids, highlighting convergence among highly fossorial clades, and allows ecological inferences for fossil species. Hierarchical cluster analysis using morphometric data allowed examination of morphological similarity among taxa and helped to secondarily support taxonomic designations for the Gray Fossil Site taxa. The resulting phenogram shows strong similarity to the most up-to-date molecular cladogram and actually matched phylogenetic relationships substantially better than any morphological cladistic analyses to date. All six recognized tribes were represented on the cluster analysis phenograms, all of the shrew moles (Scaptonychini, Urotrichini, and Neurotrichini) clustered together, and there was some separation between the tribes Talpini and Scalopini. Additionally, the cluster analysis provides new information about the placement of fossil taxa and which parts of the tree still need better resolution.