Palaeoecological investigations on Plio-Pleistocene European rhinoceroses (genus Stephanorhinus): Powder X-ray diffraction, carbone isotope geochemistry , tooth wear analyses and biometry

The project investigates the palaeoecology of European Plio-Pleistocene rhinoceroses (genus Stephanorhinus) in order to bring to a better understanding of the evolutionary history of the genus. The four species on the focus of our research show a wide degree of adaptability to different environmental contexts thus studying their palaeoecology (size variation, diet adaptation, niche partitioning) is of paramount interest to shed light on the evolution of natural systems in the past. This concentrates in particular on the diet through an interdisciplinary approach: carbon isotope (that needed paired powder X-ray diffraction analysis), mesowear, 3D microwear texture analysis and biometry. We collected samples of rhinoceroses’ bone from the Pliocene to the Middle Pleistocene, to perform carbon isotope analysis, and used powder X-ray diffraction to assess the validity of the isotopic signal. The only Middle Pleistocene locality of Mosbach gives appreciable results, showing a generalist diet comparable to the modern Rhinoceros unicornis for both the rhinoceroses, S. hundsheimensis and S. kirchbergensis, while in earlier localities the isotopic signal in bone is altered (high crystallinity). Since the ecology of the species S. megarhinus (Pliocene), S. elatus (Late Pliocene) and S. etruscus (Early Pleistocene), has not been previously investigated in the literature, and since the isotopic signal is not valid in these earlier species, we approached the study of their ecology through the analysis of their teeth at different levels: morphobiometry, mesowear and 3D dental texture microwear analyses. The three species show a similar diet, the mesowear score places these species between the browser modern species, D. sumatrensis and R. sondaicus, and the mixed feeder, R. unicornis, so they were not pure browsers but neither as generalists as the Pleistocene S. hundsheimensis (which is closer to R. unicornis by the previous geochemical results). Since the ecology of these different species is the same, doubts arise about the supposed coexistence of two species. These three related species have the same diet despite the climatic fluctuations from the Pliocene to the Early Pleistocene, and the difference in size, indicating the wide flexibility of the whole taxon. Among fossil rhinoceroses, S. hundsheimensis had been recognized by several author as an extremely flexible species, characterized by high adaptability and plasticity. Given its wide recorded size range, we studied in detail its geographical and chronological size variation. The supposed distinction of two chronological distinct forms (small and large form) is not confirmed by our results which highlights the main influence of local environmental factors driving the size variation of this flexible species through time in different regions.