Homme et Environnement, MNHN - Musee de l'Homme
April 17, 2020 , Diamond 6
One of the core challenges for paleoanthropologists is to assess early hominin locomotor behavior from often incomplete fossil remains. The increasing availability of 3D imaging, combined with current geometric morphometric (GM) approaches, offers the possibility to quantitatively compare morphological shapes not easily described with linear measurements. We illustrate this by conducting a 3D GM analysis of the humerus in extant hominoids and fossil hominins, in order to further document morphological differences related to locomotion in extant forms and to infer locomotor behavior in extinct forms. A sample of 100 humeri of extant apes (Gorilla, Pan, Pongo, Hylobates) and modern humans was surface-scanned. Fossil casts of early hominins, assigned to Paranthropus, Australopithecus and Homo, were also included. A total of 186 standard landmarks and semilandmarks were extracted and, after sliding the semilandmarks, Procrustes-aligned. Overall shape affinities of the complete humerus and the distal articular surface were assessed using Principal components analysis and within- and between-group Procrustes distances. The results confirm previously documented differences between major locomotor groups, with Hylobates having the most distinct shape. Human humeri are distinct as well, though show some overlap with Pan. Procrustes distances provide insight into how well fossil hominins fit into extant patterns. According to our findings, the humerus shape of australopiths, including Au. sediba and Au. anamensis, is most similar to Orangutan, followed by chimpanzees and humans. However, the lack of clear difference between hominins and extant Apes is compatible with a wider range of locomotor behavior, rather than with a specialized one.