Geometric morphometrics of vole ( Microtus californicus) dentition as a new paleoclimate proxy: Shape change along geographic and climatic clines

Abstract

Quaternary small-mammal fossils are widespread and have served as valuable paleoclimatic proxies through niche-modeling or otherwise relating presence-absence data to climatic data. This paper examines the potential for a new, more resolved type of paleoclimate proxy in the form of Microtus tooth shape, using an abundant California species, Microtus californicus. Geometric morphometrics and partial least squares analyses are used to find geographic signals in the shape of the first lower molar (m1) of this species. M. californicus m1s are relatively straight in the northwest, cooler, moister portion of California and more curved in the southeast, hotter, drier portion of the state. These tooth shape changes may be a result of selection related to different vegetation ultimately controlled by climate, and therefore diet, within the species' range. The pattern in m1 shape persists when phylogeographic hypotheses are taken into account, indicating that the climate signal is significant independent of intraspecific groupings. This method adds an important new tool to the suite of proxies available to reconstruct past climates at fine spatiotemporal scales and reveals a geographic/climatic signal that correlates with morphological variation across the range of M. californicus.