The Neurocranium of Anasinopa leakeyi (Hyaenodonta, Mammalia) – a First Insight into Teratodontine Brain Morphology

Sammanfattning: The Hyaenodonta include a wide variety of carnivorous mammals ranging in age from late Palaeocene to middle Miocene. Although they reached a nearly global distribution, little remains of them today. Many of the taxa are based only on teeth and jaw fragments. If we are to understand how these animals lived and evolved, we must therefore make the most out of the material we have. Herein, I report on the first nearly complete skull of Anasinopa leakeyi (Teratodontinae), which was recently found in Northern Kenya. The skull is dorsoventrally compressed, but otherwise relatively undamaged. The aim of this study was to provide a first glimpse of teratodontine brain morphology by reconstructing the neurocranium of this skull and creating a digital endocast. The result was one of the most well preserved endocasts of any hyaenodont known to date, with many of the cranial nerves and blood vessels visible. The size of the optic foramen relative to the size of the brain is similar to that of the extant wolf, Canis lupus, suggesting that A. leakeyi may have had a similar visual acuity. The body mass of A. leakeyi was estimated to up to 25 kg, meaning that it may have hunted small or large animals, perhaps having the ability to shift to larger prey when needed, as do extant, similarly sized, Felidae and Canidae. Endocasts are known from only a handful hyaenodont species, many of which were described by Radinsky in 1977. However, little work has been done on hyaenodont brains since then. The second aim of this study, therefore, was to place these hyaenodont brains, and particularly that of A. leakeyi, in the most recent phylogenetic framework, to better understand how the brain evolved in this group. This suggests that the evolution of a larger, more convoluted neocortex occurred convergently in several clades of Hyaenodonta. Furthermore, the presence of only a single neocortical sulcus in the earliest hyaenodonts calls into question the previous hypothesis of an ancestral pattern with two sulci for Artiodactyla, Perissodactyla and Carnivora. This study provides a basis for future research on brain evolution in Hyaenodonta, as well as showcases the possibilities offered by 3D technology.