Discovery of the skull of Stephanorhinus kirchbergensis (Jager, 1839) above the Arctic Circle

The skull of the extinct rhinoceros Stephanorhinus kirchbergensis (Jager, 1839) was discovered in the Chondon River valley (Arctic Yakutia, Russia) during the summer of 2014. This is the first find of Stephanorhinus above the Arctic Circle, expanding significantly the known geographic range of the genus. C-14 dating and geologic evidence indicate that the skull dates to between 48,000 and 70,000 yr, corresponding to Marine Oxygen Isotope Stage 4/3. It is thus among the latest records of this species. To explore the evolutionary and natural history of this relatively unknown animal, we performed morphological, dietary, and genetic analyses. Phylogenetic inference based on a complete mitochondrial genome sequence confirms the systematic placement of Stephanorhinus as most closely related to the extinct woolly rhinoceros, Coelodonta. Food remains in the fossas of the cheek teeth, identified as Larix, Vaccinium, Betula sp., Aulacomnium, and dicotyledonous herbs and grasses, suggest a mixed feeder's diet. Microwear analysis suggests that, during the last months of its life, this individual fed predominantly on leaves and twigs. The habitat of Stephanorhinus comprised grassland and open woodland that were characterized by moist and cold climate conditions, similar to those in the region today.