Enamel carbon, oxygen, and strontium isotopes reveal limited mobility in an extinct rhinoceros at Ashfall Fossil Beds, Nebraska, USA

Ashfall Fossil Beds in Nebraska, USA, was a mid-Miocene (11.86 ± 0.13 Ma) watering-hole that preserved hundreds of herbivores in volcanic ash. The short-legged, barrel-bodied rhinoceros, Teleoceras major (Mammalia; Rhinocerotidae), is abundant at Ashfall (> 100 individuals), leading some researchers to suggest individuals formed large groups, while others have argued they congregated at Ashfall seeking refuge from the ash that ultimately caused their death. Here, we evaluated three types of mobility-natal dispersal of subadults, seasonal migration, and response to natural disaster-using carbon, oxygen, and strontium isotope ratios in tooth enamel from thirteen T. major adult individuals. We bulk and serially sampled enamel from mandibular second and third molars, which should respectively record behaviour after weaning but before and after possible natal dispersal. Results indicate that all sampled individuals had limited mobility and were local to Ashfall. Semi-aquatic adaptations likely restricted T. major to wet habitats and prohibited long-distance movement. Social (rather than spatial) dispersal, seasonal dietary flexibility, and elevated Miocene primary productivity could have allowed individuals to maintain genetic diversity and avoid depleting local resources. Reconstructing how extinct ungulates utilized ancient landscapes provides important context for understanding their paleoecology and sociality as well as the environments they inhabited.