Extended Data Fig. 9: Calcar femorale morphology in extant hominines.
From: Postcranial evidence of late Miocene hominin bipedalism in Chad
The selected individuals corresponds to morphological extrema, i.e., the minimal and maximal degrees of expression of the calcar femorale, in our comparative sample (wild caught specimens). The boxes are for a, modern humans; b, chimpanzees (Pan paniscus); c, chimpanzees (Pan troglodytes); d, gorillas. For each box, parasagittal views are on the left (taken at the maximal possible degree of expression of the calcar femorale, around mid-width of the lesser trochanter, see lower right panel); transversal views are on the right (taken at the maximal possible degree of expression of the calcar femorale, ca at the proximal border of the lesser trochanter, see lower right panel). The asterisk marks an evidence of a calcar femorale. The calcar femorale is present in all modern humans of our sample; in parasagittal view, its expression displays a columnar aspect with an oblique orientation. The trabecular bundle forming the CF shows various degree of densification and thickness, from loose (e.g., third specimen from the top) to tightened (e.g., first and fourth specimens from the top). In transversal view, the CF forms a rather short spur originating from the thickened medial cortical bone. By contrast, most of our sampled non-human apes do not show any evidence of a columnar and oblique trabecular bundle. At best, a thin, curved, cancellous bone densification is identifiable in parasagittal view. In transversal view, the CF, when present, corresponds to a thin ray composed of few or single trabeculae, contrasting in this aspect with the modern human condition. Besides, the degree of development of the CF is associated with a relative thickening of the antero-medial cortical bone, but with a less extent in non-human apes than in modern humans. In modern humans, the thickening tends to be more medial than antero-medial. This configuration potentially enlightens the results from29 showing a lengthened CF in modern humans compared to non-human apes, as the absolute CF length was measured from the tip of the CF to the exterior cortical boundary.
