STABLE ISOTOPES IN ENAMEL: HOW IT HAS CHANGED WHAT WE KNOW ABOUT EMBRITHOPODS

The radiation of embrithopods from Northern Africa to the Eocene island of Pontides has posed a peculiar problem. Originally, researchers thought these mammals were semi- or fully-aquatic, based on their morphology, which means that they would have had the means to swim across the Neotethys sea that separated the two landmasses. However, recent stable isotope research completed by Clementz et. al. (2008) concluded that embrithopods are terrestrial, discrediting the widely accepted means of dispersal. It is important to understand if embrithopods in general were aquatic because it will shed light on how this group of African mammals ended up on the Eurasian island of Pontides during the middle Eocene (Lutetian), in addition to the general lifestyle of the group. Although morphology points to an aquatic lifestyle for the mammalian species, our measurements of the δ¹⁸O isotopic fractionations preserved in tooth enamel paints a different story. We compared the isotopic composition of tooth enamel from Palaeoamasia, a Eurasian embrithopod, to that of a known terrestrial mammal from the same region, Hilalia. The embrithopod δ¹⁸O values fell within the Hilalia range of 20.99 ‰ to 18.96 ‰ (VSMOW), with a p-value of 0.4694. These results suggest that Palaeoamasia inhabited a similar terrestrial ecosystem, putting into question the previously accepted aquatic lifestyle of the mammal and the ability to swim from Northern Africa to Pontides. If embrithopods were in fact a terrestrial group, they would have had to walk, or swim short distances, along carbonate shelves between islands until they reached Pontides. Our research has also shown that tooth enamel can preserve carbon and oxygen isotopes with minimal replacement or diagenesis, making it a good source for stable isotopes in future studies.