Feeding strategies of circum‑Mediterranean hipparionins during the late Miocene: Exploring dietary preferences related to size through dental microwear analysis

Abstract

The adaptive radiation of hipparionins after their Old World dispersal was linked with a trend towards smaller body sizes. The appearance of the small-sized forms has usually been associated to open environments and grazing diets. A recent approach, moreover, highlights the role of life history modifications related to habitat conditions as triggers of their size shifts. Here, we test the relationship between hipparionin size and diet analyzing the dental microwear textures of different-sized hipparionins from Vallesian and Turolian circum-Mediterranean localities. Our results show that hipparionins were mainly mixed-feeders and that there was no general link between body size and diet. However, we identified broader feeding spectra in western Mediterranean smaller forms and more specialized grazing diets in larger ones, a differentiation not found in the eastern Mediterranean hipparionins. At odds with the notion of more open habitats eastward, we detected a larger browsing component in eastern hipparionin diets. The consumption by extant equids of more woody browse during the dry season leads us to propose a greater seasonality as a possible cause. Considering the arguable role of external abrasives on the microwear, another interpretation might involve the presence of more grit in the eastern opener habitats. Interestingly, we found that sympatric hipparionins tend to have similar feeding habits, which points to the fact that their diets were influenced by the local environment. Our results, then, suggest that the small size of some hipparionins resulted from different selective pressures rather than to a general adaptation to increasing habitat opening.

Evolutionary paleoecology of European rhinocerotids across the Oligocene-Miocene transition

“…Mesowear ruler is rather stable across time, space and taxa, with most species having a mean mesowear ruler comprised between 1.5 and 2 at the different localities. Similarly to other studies (Mihlbachler and Solounias, 2002;Saarinen et al, 2016;Orlandi-Oliveras et al, 2022), we did not find a clear relationship between body mass and mesowear.…”

“…Mesowear score is rather stable across time, space and taxa, with most species having a median mesowear score around 2 at the different localities. Similarly to other studies [77][78][79], we did not find a clear relationship between body mass and mesowear, suggesting once again that the classical assumption of greater tolerance for a lower quality diet in larger species lacks empirical support [80].…”