Using virtual endocast to measure total endocranial volume of Orkhon hyena fossils

During 2021-2024, the Russian-Mongolian-American expedition studied the Pleistocene faunal complexes of the Khangai and Gobi Altai Mountains and Mongolia in general. The species composition of these complexes remained poorly studied due to their fragmentation and small number of animal bone remains. New finds make it possible to significantly expand the list of Pleistocene mammal species that inhabited this territory, as well as to reinterpret samples from the old collections. Since the bones of fossil mammals are usually poorly preserved, bear traces of natural and anthropogenic destruction, and animal gnawings, various digital methods can be used. To study a sample of the skull of a fossil hyena from the Bag-Nariin-am hollow in the Orkhon River valley in Central Mongolia, we used computer tomography. This is a non-destructive method that allowed us to reconstruct a virtual endocast of the brain together with the frontal sinuses, and measure its total volume. We compared the obtained volume with published values for the brain volumes of extinct and extant hyaenids. The article discusses the history of the dispersal of two species of cave hyenas-Crocuta spelaea and Crocuta ultima-in Asia, and the role of the territory of modern Mongolia as a border between the ranges of these two species in the Upper Pleistocene. In addition, Mongolia could be one of the last habitats of cave hyenas: the results of excavations in Tsagaan-Agui Cave in 2021-2024 indicate the presence of hyenas in the lower part of layer 2.1, dating back to the middle of the Last Glacial Maximum-the time, by which Crocuta crocuta had already disappeared from Siberia, and finds of C. ultima in Southeast and East Asia became extremely rare.