Multiproxy dietary trait reconstruction in Pleistocene Hippopotamidae from the Mediterranean islands

Bethune and colleagues compare the teeth of four extinct hippopotami from Cyprus, Crete, Malta and Sicily with those of the living Hippopotamus amphibius. Dental topography and enamel surface texture are used together to ask how tooth form and feeding behaviour relate to the resources, habitats and animal communities of each island. Topography is treated as a longer-term indicator of inherited adaptation and texture as a shorter-term signal of what an animal was eating, which, the authors argue, lets the two separate inherited traits from individual foraging.

The sample holds Hippopotamus pentlandi, Hippopotamus melitensis, Hippopotamus creutzburgi, Phanourios minor and the living reference species, with 5 to 16 individuals per species. Adult teeth at an intermediate wear stage were chosen, upper second molars for topography and mainly for texture, with some first molars of H. creutzburgi and third molars of P. minor added to the texture analysis. The teeth were moulded and cast, three-dimensional occlusal models were built and their mean surface slope calculated in SAGA-GIS, and enamel facets were measured under a confocal microscope against thirty ISO surface texture parameters. Statistical comparisons use trimmed data and robust tests. Repositories, localities and dates are set out in Table 1.

The Cypriot material is Phanourios minor, attributed to Ayia Irini, Kissonerga, Dhikomo and Oschin, with one specimen of unknown locality. Table 1 gives ESR-based date ranges for some of these samples and notes that the age information follows the collection attributions.

The argument

Mean occlusal slope rises from H. pentlandi and H. amphibius through H. melitensis and H. creutzburgi to P. minor. The larger, more hypsodont hippos have the lowest relief, the medium-sized species an intermediate relief, and the smallest, brachyodont P. minor the highest. Enamel textures place H. melitensis and P. minor as rougher, H. pentlandi as less dominated by abrasion, and H. amphibius and H. creutzburgi as smoothest.

Island size, access to fresh water, competition and changing climate are the factors the authors link to these differences. They propose that reduced freshwater could mean more arid conditions and more abrasive forage, and that resource limits on smaller islands could favour broader diets. H. creutzburgi's texture is read as consistent with fresh-grass feeding and with seasonal access to the lake at Katharo; H. pentlandi is placed in a niche like the mainland form's but with more abrasives in the diet; H. melitensis is given a variable, possibly broadened diet.

Phanourios minor

For P. minor the authors weigh two explanations of its variable enamel texture: a broader dietary niche in a habitat with little competition, or a dietary shift tied to climate change around the Pleistocene–Holocene transition. They conclude that the two-proxy approach identifies distinct dietary traits among the island species.