Variations in hypsodonty of ungulates: testing its utility as a climatic proxy in modern and Late Pleistocene mammal communities

The quantification of past levels of precipitation is frequently challenging in fossil localities where limited suitable proxies are present. Recent work has suggested that hypsodonty (tooth crown height) in mammals can be used as a predictor of mean annual precipitation in both modern and fossil contexts. However, previous research on modern hypsodonty-climate relationships was largely based on per species mean hypsodonty at spatial scales of ecoregion level mammal communities, a coarse spatial resolution compared to what is seen in regional and local differences in precipitation. In addition, intraspecific variation in hypsodonty had not been previously tested in a thorough and adequate manner to permit the use of per species mean hypsodonty in palaeoenvironmental reconstruction.

This research reassesses the modern relationship between hypsodonty and climate,
departing from the use of per species mean hypsodonty, and instead focussing on
individual tooth hypsodonty index (using the lower third molar) and locality mean
hypsodonty index, with the ultimate goal of applying this method to Quaternary
mammalian dental material. A large dataset of 3,788 hypsodonty index measurements
was created from well-provenanced museum specimens representing 148 ungulate taxa from 950 unique localities. Correlations of these measurements with modelled climate data were then tested at the resolution of individual localities rather than large
ecoregions. Results show that, contrary to previous work, correlations between
hypsodonty index and precipitation-related climate variables are weaker than for those with temperature-related variables, although no correlations are particularly strong, including testing the inclusion of both individual left and right teeth and migratory taxa in the dataset. This highlights not only the complex nature of hypsodonty and its possible controls but also indicates that (1) scale and rate of change in individual and community hypsodonty index need to be considered both temporally and spatially, and (2) that current models are not robust enough for further application.

In order to establish whether the method could detect abrupt climatic and environmental change during the Late Pleistocene, hypsodonty index data was collected from seven well-dated Late Pleistocene Mediterranean cave sites. The Mediterranean was selected as the spatial focus as it is largely assumed that precipitation and moisture availability are the dominant factors influencing environmental change. Mean hypsodonty index of fossil mammal communities through these sequences was compared to existing palaeoecological and geochemical proxies to validate its utility in palaeoenvironmental reconstruction. It is clear that the method’s validity is highly dependent on presence, availability and condition of the fossil material and that low sample sizes and differential resolutions between proxies drastically reduce reliability. Environmental and climatic inferences can, however, be made with caution but are site-specific in nature.