Locomotor adaptations and the origin of the hominin pelvis (335.4)

Abstract

The bony pelvis is involved in many aspects of an animal’s biology, and what factors shaped the unique form of the human pelvis has received a great deal of attention in paleoanthropology. Not only does the bony pelvis surround the birth canal, but it anchors lower limb muscles and reflects the shape of the bony torso. Torso shape and lower limb function are integrally related to locomotor adaptation, and so either or both can affect obstetric adaptations. Because extant great apes share a similar pattern of pelvic morphology with broad, coronally oriented iliac blades and long lower pelvis, for many years it was reasonable to hypothesize that this represented the ancestral condition for hominins, and that the transition to habitual terrestrial bipedal locomotion involved substantial selection to reorient the ilia and shorten the pelvis, and thus restrict the bony birth canal. However, recent fossil evidence from Miocene and early Pliocene hominoids, notably Rudapithecus hungaricus (9 ma, Rudabanya, Hungary) and Ardipithecus ramidus (4.4 Ma, Aramis, Ethiopia) suggest that the pattern of selection that shaped the hominin pelvis may not have involved a drastic reduction in iliac length and reorientation, but that other factors such as spinal mobility and hip joint orientation played a much greater role than previously thought in influencing the size and shape of the birth canal in early hominin evolution.