Brief communication: Lumbar lordosis in extinct hominins: implications of the pelvic incidence.

Recently, interest has peaked regarding the posture of extinct hominins. Here, we present a new method of reconstructing lordosis angles of extinct hominin specimens based on pelvic morphology, more specifically the orientation of the sacrum in relation to the acetabulum (pelvic incidence). Two regression models based on the correlation between pelvic incidence and lordosis angle in living hominoids have been developed. The mean values of the calculated lordosis angles based on these models are 36°-45° for australopithecines, 45°-47° for Homo erectus, 27°-34° for the Neandertals and the Sima de los Huesos hominins, and 49°-51° for fossil H. sapiens. The newly calculated lordosis values are consistent with previously published values of extinct hominins (Been et al.: Am J Phys Anthropol 147 (2012) 64-77). If the mean values of the present nonhuman hominoids are representative of the pelvic and lumbar morphology of the last common ancestor between humans and nonhuman hominoids, then both pelvic incidence and lordosis angle dramatically increased during hominin evolution from 27° ± 5 to 22° ± 3 (respectively) in nonhuman hominoids to 54° ± 10 and 51° ± 11 in modern humans. This change to a more human-like configuration appeared early in the hominin evolution as the pelvis and spines of both australopithecines and H. erectus show a higher pelvic incidence and lordosis angle than nonhuman hominoids. The Sima de los Huesos hominins and Neandertals show a derived configuration with a low pelvic incidence and lordosis angle.