Growth and development provide critical information about the evolutionary history of early hominin adult morphology. Using fossils from the southern African site of Kromdraai, we herein present the digital models of three juvenile specimens that are especially valuable because they shed light on how the distinct adult craniofacial characteristics of Paranthropus robustus developed. We find significant differences in the development of P. robustus and Australopithecus africanus. Additionally, some features of the P. robustus specimens suggest that the iconic SK 54 juvenile calvaria from the southern African site of Swartkrans is more likely an early Homo specimen rather than Paranthropus. The results of this study shed light on the evolutionary relationships between different early hominin species and could help to identify the closest relative to the Paranthropus/Homo clade.

Specimens

The three Paranthropus robustus infant specimens numbered KW 6420, KW 9000/9600 and KW 10840 from Kromdraai are curated at the Evolutionary Studies Institute, University of the Witwatersrand in Johannesburg, South Africa. Researchers may apply for access through the University Fossil Access Advisory Committee by contacting the University Curator for Fossil and Rock Collections: Bernhard Zipfel, PhD, University Curator of Fossil and Rock Collections, Evolutionary Studies Institute, University of the Witwatersrand, Johannesburg (e-mail: Bernhard.Zipfel@wits.ac.za)

X-ray micro-computed tomography and 3-D digital (.stl) models

The X-ray micro-computed tomography scanning was performed at the University of the Witwatersrand (Johannesburg, South Africa) using the Nikon Metrology XTH 225/320 LC dual source industrial CT system, and at the South African Nuclear Energy Corporation (Pelinbada, South Africa) using the Metris X-Tek XT H225L. The specimens were scanned at a voltage of 120kV and current of 130μA with isometric voxel dimensions ranging from 10 to 36 µm. An ‘.stl’ file (or digital model) of each specimen was obtained in Avizo Standard 8.1.1 (www.thermofisher.com) from micro-CT data.

The three data files can be opened using ‘MeshLab’, a free and open-source software (version 2 or later) that is dedicated to the processing of meshes (or digital models). For more information, please visit: https://en.wikipedia.org/wiki/MeshLab