Small Mammal Hypsodonty Ratios Do Not Track Precipitation Changes at Natural Trap Cave, Wyoming

Abstract

With future climate change, drought events are expected to increase. Hypsodonty is an adaptation in herbivorous mammals for higher crowned teeth, which are better able to process coarse foods. Typically, animals with highly hypsodont teeth are found in arid places. This trait is considered an adaptation to aridity and drought. Many studies examined the spatial distribution of hypsodonty with respect to climate in both ungulates and Glires (rodents and lagomorphs). However, few studies have examined whether spatial trends play out across known climate shifts at a single location. Glires evolved hypsodonty millions of years before ungulates, adapt readily due to short generation times, and have relatively small home ranges, so they may provide more accurate climate predictions. Here, we use Glires from Natural Trap Cave, WY to examine whether community-level changes in hypsodonty reflect known precipitation changes. Additionally, this study investigates the effects of measurement techniques (teeth in-jaw versus out-of-jaw) and tooth wear on hypsodonty measurements. Currently, most hypsodonty studies try to use only completely unworn teeth, which are difficult to find in the fossil record. We find that community-level hypsodonty did change over time, but not in ways that corresponded with established precipitation values at Natural Trap Cave. There were likely other factors driving hypsodonty levels within this community, such as an increasing abundance of grasses with increases in temperature and precipitation. Tooth wear did not seem to have significant effects on hypsodonty measurements across time, and tooth wear only sometimes significantly affected hypsodonty measurements across taxa. With further analysis, it might be conclusively decided that samples can be expanded to somewhat worn teeth. This analysis of hypsodonty as a climate proxy can help shape both its use in future studies and our understanding of how species will respond to future climate changes.