The Menu for Ancient Humans 1.9 Million Years Ago

Using non-invasive high-resolution computed tomography technology and shape analysis the authors deduced the main direction of loading during mastication (chewing) from the way the tooth roots are oriented within the jaw. By comparing the virtual reconstructions of almost 30 hominin first molars from South and East Africa they found that Australopithecus africanus had much wider splayed roots than both Paranthropus robustus and the East African Paranthropus boisei. “This is indicative of increased laterally-directed chewing loads in Australopithecus africanus, while the two Paranthropus species experienced rather vertical loads”, says Kornelius Kupczik of the Max Planck Institute for Evolutionary Anthropology.

Paranthropus robustus, unlike any of the other species analysed in this study, exhibits an unusual orientation, i.e. “twist”, of the tooth roots, which suggests a slight rotational and back-and-forth movement of the mandible during chewing. Other morphological traits of the P. robustus skull support this interpretation. For example, the structure of the enamel also points towards a complex, multidirectional loading, whilst their unusual microwear pattern can conceivably also be reconciled with a different jaw movement rather than by mastication of novel food sources. Evidently, it is not only what hominins ate and how hard they bit that determines its skull morphology, but also the way in which the jaws are being brought together during chewing.

The new study demonstrates that the orientation of tooth roots within the jaw has much to offer for an understanding of the dietary ecology of our ancestors and extinct cousins. “Perhaps palaeoanthropologists have not always been asking the right questions of the fossil record: rather than focusing on what our extinct cousins ate, we should equally pay attention to how they masticated their foods”, concludes Gabriele Macho of the University of Oxford.

Molar root variation in hominins is therefore telling us more than previously thought. “For me as an anatomist and a dentist, understanding how the jaws of our fossil ancestors worked is very revealing as we can eventually apply such findings to the modern human dentition to better understand pathologies such as malocclusions”, adds Viviana Toro-Ibacache from the University of Chile and one of the co-authors of the study.

Contacts and sources:
Dr. Kornelius Kupczik / Sandra Jacob
Max Planck Institute for Evolutionary Anthropology, Leipzig

Prof. Gabriele Macho
School of Archaeology
University of Oxford

Citation: Kornelius Kupczik, Viviana Toro-Ibacache, Gabriele A. Macho
On the relationship between maxillary molar root shape and jaw kinematics in Australopithecus africanus and Paranthropus robustus
Royal Society Open Science 5: 180825