Ecomorphological analysis of bovid remains from the Plio-Pleistocene hominin-bearing deposit of Unit P at Kromdraai, South Africa

Abstract

The site of Kromdraai is known for the first discovery of Paranthropus robustus remains. Research conducted at Kromdraai shows its rich fossiliferous deposits, geological complexity and potential to highlight the evolutionary history of Plio-Pleistocene hominin lineages in a dynamic and changing environment. Here, we provide the results of the first application of ecomorphology to bovid postcranial specimens from the newly excavated deposit of Kromdraai Unit P (KW-Unit P). Four anatomical elements of the bovid skeleton were measured and examined as they represent locomotion and substrate interaction: the astragalus and the proximal, intermediate and distal phalanges. Four discriminant function analyses (DFA) were conducted to determine each element’s ability to predict habitat affiliation accurately. This was done by comparing the morphologies of the fossil specimens to modern bovids found in broadly defined habitats (open, light cover, heavy cover, and forest). For the modern assemblage, the DFA cross-validation tests correctly returned classifications ranging from 58.8% to 72.0% in a four-habitat system for the four bone elements. Fossil results revealed that bovids from KW-Unit P had varied morphological adaptations to open and light cover habitats (91.7% combined) with few forest (4.7%) and heavy cover (2.3%) adaptations. This indicates that during the deposition of KW-Unit P, the environment was open with savanna grasslands, tall grasses and light bushes. Forest which is a continuous tree canopy and heavy cover environments represented by dense woodlands and bushes were also present to a lesser degree. Overall, KW-Unit P is characterized as a mosaic with more open and light cover habitats indicating open savanna and grasslands, a riparian forest, woodlands and bushes.These reconstructions are consistent with previous palaeoenvironmental interpretations for KW-Unit P and Kromdraai B (KB) as a whole. Since our results are not entirely limited to KW-Unit P, we, therefore, argue that Paranthropus robustus found at Kromdraai thrived in mosaic environmental settings around the time when open habitats were dominant.