When did spotted hyenas become social? Evidence from fossil endocasts

Abstract The spotted hyena, Crocuta crocuta , is a highly social carnivore with several unique traits showing advanced social behavior. Studies of the brain of living spotted hyenas show that the anterior cerebrum is enlarged, a feature linked to sociality. It is not known, however, when sociality evolved in spotted hyenas, and its evolutionary context is therefore unknown. This is important to understand due to the apparent negative fitness effects of some spotted hyena traits. Studies of extinct species of Crocuta have shown that these do not share the large anterior cerebrum of the extant species. We use computed tomography (CT) scanning to study the endocranium of a >350,000-year-old spotted hyena from Megenta, Ethiopia and compare it to a sample of modern specimens representing the four living Hyaenidae species. We also compared our results to published fossil hyena endocrania. We found that the brain of the Ethiopian fossil is indistinguishable from that of the extant species and different from all other fossil and extant hyena brains. This places a minimum age of 350,000 years on the evolution of spotted hyena sociality and eliminates factors such as selective pressure from early Homo sapiens as potential drivers of sociality.