The ecological context of the Early Pleistocene hominin dispersal to Asia

The ecological context of the first known dispersal of Homo into East Asia is investigated here using information from large mammals, and particularly from carnivores. The aims were to determine whether hominins occurred in similar ecological contexts compared with sites in East Africa, and whether carnivore guilds in East Asia and East Africa were similar in composition in terms of ecologically comparable species. To answer these questions, dental measurements were taken on large mammalian specimens from East Asian Plio-Pleistocene sites, including hominin and non-hominin sites, and from specimens found at Olduvai Gorge and Lake Turkana in East Africa. Dental measurements were taken to estimate body mass and hypsodonty, as well as ecomorphological characteristics in carnivores. Each large mammal species was classified as an ecotype, which is a combination of body mass, diet and substrate (i.e., terrestrial, arboreal and aquatic) characteristics. The ecotype analysis shows that East Asian and East African fossil sites were significantly different from each other in ecological structure, with the Asian sites having a greater concentration of browsers and mixed feeders, while East African sites had more grazers. The East Asian hominin sites included varied ecological structures, implying that hominins were not tied to a single type of environment on their initial dispersal. Carnivore ecomorphological indices related to body mass and feeding adaptations, such as the amount of the dentition devoted to slicing, grinding and bone-cracking. Carnivore guilds containing sets of species with similar feeding adaptations and body mass would have presented similar opportunities for scavenging and degrees of competition for hominins. The Hyaenidae differed between Africa and Asia in features related to fourth premolar size. Omnivorous ursids were present in Asia but not in Africa. In East Asia, there were also decreases in the number of species of Hyaenidae and Canidae from the Late Pliocene to the early Pleistocene. Despite this, the remaining Asian hyaenid, Pachycrocuta, would have been a formidable competitor for scavenging hominins. Overall, hominins occurred in varied ecological settings, and competed with a carnivore guild that had species with different adaptations compared with Africa.