Molar biomechanical function in South African homininsAustralopithecus africanusandParanthropus robustus

Abstract

Diet is a driving force in human evolution. Two species of Plio-Pleistocene hominins, Paranthropus robustus and Australopithecus africanus , have derived craniomandibular and dental morphologies which are often interpreted as P. robustus having a more biomechanically challenging diet. While dietary reconstructions based on dental microwear generally support this, they show extensive dietary overlap between species, and craniomandibular and dental biomechanical analyses can yield contradictory results. Using methods from anthropology and engineering (i.e. anthroengineering), we quantified the molar biomechanical performance of these hominins to investigate possible dietary differences between them. Thirty-one lower second molars were 3D printed and used to fracture gelatine blocks, and Bayesian generalized linear models were used to investigate the relationship between species and tooth wear, size and shape, and biomechanical performance. Our results demonstrate that P. robustus required more force and energy to fracture blocks but had a higher force transmission rate. Considering previous dietary reconstructions, we propose three evolutionary scenarios concerning the dietary ecologies of these hominins. These evolutionary scenarios cannot be reached by investigating morphological differences in isolation, but require combining several lines of evidence. This highlights the need for a holistic approach to reconstructing hominin dietary ecology.

Changing perspectives on early hominin diets

“…Deciphering the diets of human ancestors has always been challenging given the complexity of primate diets, the idiosyncratic nature of fossil preservation, the luck and skill in finding fossils, the expertise in preparing those fossils, and the palimpsestic nature of their deposits. In fact, the task is sufficiently complex that analyses can only benefit from so-called multi-proxy approaches, with short-term dietary inferences (the so-called direct methods, or foodprints, mentioned here) providing certain types of data and long-term dietary inferences (such as morphological and biomechanical analyses) providing others ( 9 ). As the former studies provide evidence of the foods that were actually eaten by an individual during the period of time that the tissue was being deposited (in the case of biogeochemistry) or the food was being chewed (in the case of dental calculus and microwear), they can provide insights into the behavior and ecology of populations.…”

“…The most common of these have focused on the fossils themselves, with traditional morphological studies generally relying on evolutionary arguments to make inferences about past functions—e.g., variations in tooth morphology being used to make inferences about the dietary capabilities of past species ( 6 – 8 ). Researchers have also made use of technological advances in the past few decades to develop new ways to quantify morphological similarities and differences (e.g., dental topographic analyses), yielding new arguments for the presence of specific behavior patterns in the past and their potential implications for paleodietary reconstructions ( 9 , 10 ). These methods certainly give us broader perspectives—for instance, insights into species-level responses to changes in food availability associated with longer-term environmental change ( 11 ).…”

Évaluation de la capacité de comminution lors de l’intercuspidation des molaires chez les catarrhines à l’aide d’un simulateur de mastication

“…Many studies are interested in the relationship between tooth morphology and the ability to fragment foods efficiently, because postcanine dentition probably evolved mostly in response to differences in the physical properties of diets (e.g. Lucas, 2004;Berthaume and Kupczik, 2021). In this study, we experimentally tested how these morphologies differ in their ability to fragment various food items during centric occlusion.…”

Anthroengineering: an independent interdisciplinary field

“…Two additional common engineering methods-FE analysis and tension/compression tests-have been used extensively in palaeoanthropology to quantify the biomechanical performance of hard skeletal tissues and address questions concerning the evolution of primate diets [12,46,58,[112][113][114]. The ability to print three-dimensional fossils further allows for the mechanical testing of previously inaccessible material [115][116][117]. These in silico and in vitro models and experiments carry with them several assumptions about the loading conditions and mechanical properties of the structure being analysed but provide valuable information about the biomechanical limits of the structure.…”