Bedane et al. (2024) provide a beautifully illustrated demonstration of the difficulties in using dental adaptation as proxies for the diets of elephants, which are in turn often used to determine the vegetation in an area. This study set out to assess mesowear, which is the relief on the teeth that forms due to abrasion by food, and therefore a good proxy of dietary composition in herbivores. The team was interested in testing whether this mesowear relates to morphological adaptations of hypsodonty (high-crownedness) and enamel thickness over a period of ~3.4–~1.1 million years in an elephant species (Elephas recki) commonly found in the Plio/Pleistocene of the Shungura formation (Omo Valley, Ethiopia). To answer this question, the team scored these metrics in 140 molars between ~3.4 and ~1.1 million years of age, separated into time bins. Their results show surprisingly low levels of variation in mesowear, indicating relatively low variation in diet that was overall mostly composed of graze (as opposed to mixed or browsing diets, which are softer). Hypsodonty and enamel thickness were correlated, but changed erratically rather than suggesting a trend towards a particular dietary adaptation. The exciting conclusion is that dental morphologies that we often consider to be adaptive to certain conditions are very slow to evolve, and that a wide variety of morphologies can support the survival of a species despite little variation in diet. For me as a functional evolutionary morphologist, this clear case of many-to-one-mapping is a timely reminder that evolution does not work either quickly or just on the one character complex I might be considering. And in terms of using elephant teeth as ecological proxies – this job clearly just got a little harder.

References

Bedane, T. G., Mackaye, H. T., and Boisserie, J.-R. (2025). New data on morphological evolution and dietary adaptations of Elephas recki from the Plio-Pleistocene Shungura Formation (Lower Omo Valley, Ethiopia). PaleorXiv, qexuf, ver. 4, peer-reviewed by PCI Paleo. https://doi.org/10.31233/osf.io/qexuf