The juvenile mandible is important in the investigation of ontogenetic and evolutionary changes among early hominins. We revisit the mandibular symphysis in juvenile specimens of Australopithecus africanus and Paranthropus robustus with two main contributions. First, we employ, for the first time, methods of computational anatomy to model complex symphyseal shape differences. Second, we present new fossil evidence from Kromdraai to improve our knowledge of symphyseal morphology. We describe differences between shapes by landmark-free diffeomorphism needed to align them. We assess which features of the mandibular symphysis best discriminate the juvenile symphysis in these fossil species, relative to the intraspecific variation observed among modern humans. Our approach eliminates potential methodological inconsistencies with traditional approaches (i.e., the need for homologous anatomical landmarks, assumption of linearity). By enabling detailed comparisons of complex shapes in juvenile mandibles, our proposed approach offers new perspectives for more detailed comparisons among Australopithecus, Paranthropus and early Homo.
The juvenile mandible is important in the investigation of ontogenetic and evolutionary changes among early hominins. To more accurately describe complex shape variations, for the first time advanced methods from computational anatomy, and new fossil evidence are used to revisit the ontogeny of the mandibular symphysis in Australopithecus africanus and Paranthropus robustus. We assess which features of the mandibular symphysis best discriminate the growing symphysis in these fossil species, relative to the intraspecific variation observed among modern humans. When compared with more traditional approaches, our results are in line with previous studies and confirm that our approach eliminates potential methodological inconsistencies with the a priori definition of homologous landmarks and the tacit assumption that anatomical shapes are linear. By enabling detailed comparisons of complex shapes in juvenile mandibles, our proposed approach offers new perspectives for more detailed comparisons among Australopithecus, Paranthropus and early Homo in both southern and eastern Africa.
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