Signs of intraspecific aggression in fossil hyenas: cranial bite punctures in <i>Adcrocuta eximia</i> and <i>Chasmaporthetes lunensis</i>

Hyaenids are an integral part of the Neogene and Quaternary ecosystems of the Old World, including some of their most specialized apex predators. However, the exact evolutionary drivers that led to the taxonomic and adaptive radiation of the hyenas are still unclear. Intraspecific aggression over territory or for social hierarchy is a common behavior in the extant members of the family, affecting many aspects of their ecological role. Here we describe a bite puncture on a skull of Adcrocuta eximia from the middle Turolian (Late Miocene) locality of Torrentet dels Traginers (Vallès-Penedès, Spain), and another one on a skull of Chasmaporthetes lunensis from the Early Pleistocene locality of La Puebla de Valverde (Teruel, Spain). The Adcrocuta puncture is located above the orbits, whereas the Chasmaporthetes one is located anterodorsally to the left orbit. Examination of external morphology and computed tomography (CT) slices reveals evidence of healing in both skulls. Based on the size and morphology of the punctures, they were probably caused by another hyena, most possibly another individual of the same species. In Chasmaporthetes, attributing the agent to Pliocrocuta or, less possibly, to an ursid or a felid is not excluded. Similar injuries are observed in specimens of extant species, including the brown and spotted hyena, showing that such trauma can occur in both social and solitary species. These specimens show that intraspecific aggression was probably present in fossil hyenas, further strengthening the resemblance between fossil and modern hyenas and providing additional information on the paleobiology of bone-crushing hyaenids.