Evolutionary paleoecology of European rhinocerotids across the Oligocene-Miocene transition

Abstract

The Oligocene-Miocene transition witnessed great environmental and faunal changes, but its drivers and consequences on mammals remain poorly understood. Rhinocerotoids are among the most affected taxa, reflected by great taxonomical (extinction of all non-rhinocerotids) and morphological (e.g., more mediportal forms) changes observed during this interval. However, potential associated changes in ecology have not been explored. Here, we investigated the paleoecology of 10 rhinocerotid species coming from 15 localities across Western and Central Europe and ranging from Mammal Paleogene reference level 28 to Mammal Neogene zone 3. We explored evolutionary trends for their diet, physiology, and habitat via dental wear, hypoplasia, body mass estimates, and stable isotopy. Our results (isotopy, dental wear) suggest that all rhinocerotids studied were C3 feeders, whether browsing or mixed-feeding, but niche partitioning was assumed at some localities: distinct dietary preferences and/or habitats were highlighted at Gaimersheim, Ulm-Westtangente, and Rickenbach, whereas a potential competition for the resources or different niche partitioning strategies (body mass, feeding height) are hypothesized at others localities (La Milloque, Thezels, Paulhiac). We reconstructed similar warm conditions at all localities except Gaimersheim, but found greater variations in precipitation. Indeed, a clear shift in delta13CCO3, enamel values was noticed at the end of the Oligocene, consistent with climatic changes (Mi-1) and vegetation modifications reported at that time. Despite these great changes, the prevalence of hypoplasia was low (< 10 %) to moderate (< 20 %) except at some localities (Pappenheim, Rickenbach, Engehalde) and for some species (Brachydiceratherium aurelianense and B. lamilloquense). Teleoceratines were particularly affected, suggesting a potential phylogenetic effect. Fourth milk molars and third molars were the most affected loci, indicating stresses around birth and environmental stresses respectively. Body mass co-variated with hypoplasia prevalence, indicating that larger species might be more susceptible to stresses and environmental changes. The tracking of rhinocerotids paleoecological preferences during the Oligocene-Miocene revealed several changes in diet and habitat (temperature, precipitation, vegetation) consistent with global changes during this period.