Indications of habitat association of Australopithecus robustus in the Bloubank Valley, South Africa

Establishing the habitat preferences of early hominin taxa is a necessary, though difficult, requirement for understanding the interaction between environmental change and hominin evolution. The environments typically associated with Australopithecus robustus have been reconstructed as predominantly open grasslands situated within a habitat mosaic that included a more wooded component with a nearby perennial water source. Most studies have concluded that the open grassland component represents the habitat preference of the hominins. In this study we investigate indicators of habitat association of A. robustus that are preserved in the animal paleocommunities represented in a series of fossil cave infills in the Bloubank Valley of South Africa, including Swartkrans, Sterkfontein, Kromdraai, and Coopers. Testing for conditions of isotaphonomy reveals a potential bias relating to depositional matrix and perhaps accumulating agent, though such a bias has not unduly influenced the taxonomic composition the assemblages. Correspondence analysis of census data from modern African nature reserves demonstrates that carnivore predation patterns are indicative of animal communities, which in turn are representative of habitats. As a result, modern census data are used to document patterns of habitat preference of large herbivores, thus allowing assignment of fossil taxa to a series of broadly defined habitat categories. Correspondence analysis of fossil assemblages reveals that the abundance profile of A. robustus is most similar to that of woodland-adapted taxa. In addition, fluctuations in the relative abundance of taxa assigned to the broad habitat categories reveal a significant negative correlation between A. robustus and open grassland-adapted taxa, indicating that the more grassland-adapted taxa there are in a given assemblage, the fewer hominins there tend to be. Thus, it appears that the open grasslands that comprise the majority of the paleoenvironments associated with A. robustus do not necessarily indicate the habitat preference of the hominins. Rather, it would appear that in addition to being dietary generalists, A. robustus were also likely to have been habitat generalists.