Life in a Central European warm-temperate to subtropical open forest: paleoecology of the rhinocerotids from Ulm-Westtangente (Aquitanian, early Miocene, Germany)

Abstract

The locality of Ulm-Westtangente yielded the richest vertebrate fauna from the Aquitanian (23.03 to 20.44 Mya; early Miocene) of Germany. Its dating to the Mammal Neogene Zone 2a, a turnover in Cenozoic climate, makes it a crucial source for the understanding of faunal, palaeoecological and palaeoenvironmental specifics of the European Aquitanian. However, if most taxa from Ulm-Westtangente have been studied, very little or nothing has been done on the large herbivores and notably the two rhinocerotids Mesaceratherium paulhiacense and Protaceratherium minutum. Here, we used a multi-proxy approach to investigate the paleoecology of these two species. The remains of the smaller species P. minutum (body mass based on teeth: 442 to 667 kg) are twice as abundant as those of the larger M. paulhiacense (1687 to 2576 kg), but both display a similar age structure with around 10 % of juveniles, 20 % of subadults and 70 % of adults. Results from mesowear, microwear, and carbon isotopes indicate different feeding preferences for the two species at Ulm-Westtangente: both were C3 feeders but M. paulhiacense had a more abrasive diet and was probably a mixed feeder inhabiting a wider range of habitats. Both species had similar mortality curves revealing four mortality peaks correlated with life events: birth or shortly after (age classes I and II), juvenile diseases (IV), weaning (VI-VII), and sexual maturity (IX-X). They were also similarly affected by hypoplasia, with about 17 % of teeth bearing at least one defect, but the most affected loci did not always correlate with the events highlighted by the mortality curves. Our study on rhinocerotids also yielded new paleoenvironmental insights, such as the mean annual temperature (19.2 {degrees}C), confirming the warm-temperate to subtropical conditions previously inferred.