B48
The foot of Ardipithecus ramidus
a primitive grasping foot

The foot of Ar. ramidus is represented by many elements of the ARA-VP-6/500 partial skeleton, supplemented by a handful of other specimens. Importantly, the articulating elements of the first and second rays of the same individual are preserved: the medial cuneiform, intermediate cuneiform, and metatarsal I. The articulating base of metatarsal II is represented by a second individual. These foot bones unambiguously demonstrate that the first ray had a strongly divergent set, comparable to the modern ape condition. This is perhaps the single most striking anatomy of Ar. ramidus, a primitive condition not known in any Australopithecus. At the same time, the Ar. ramidus foot lacks the enhanced mobility seen in that of modern apes. This relates to the toe-off capacities of the lateral foot during bipedal walking. In concert with the pelvic evidence, the Ar. ramidus foot attests to a combination of terrestrial bipedal walking with a significant degree of arboreal behavior. 　(Gen Suwa)

References

Lovejoy, C. O., Latimer, B., Suwa, G. et al. (2009) Combining prehension and propulsion: The foot of Ardipithecus ramidus. Science 326: 72e1-e8.