New first metatarsal (SKX 5017) from Swartkrans and the gait of Paranthropus robustus

Abstract

A new, complete hallucal metatarsal (SKX 5017) was recovered from the “lower bank” of Member 1 at Swartkrans (ca. 1.8 m.y. BP). The new metatarsal is attributed to Paranthropus robustus, the predominant hominid found in Member 1 (>95% of hominid individuals). SKX 5017 is similar to Olduvai Hominid 8‐H from bed I, Olduvai (ca. 1.76 m.y. BP), and both resemble humans most closely among extant hominoids. The base, shaft, and head of SKX 5017 suggest human‐like foot posture and a human‐like range of extension (= dorsiflexion) at the hallucal metatarsophalangeal joint, while at the same time the distal articular surface indicates that a human‐like toe‐off mechanism was absent in Paranthropus. The fossil evidence suggests that Homo habilis and Paranthropus may have attained a similar grade of bipedality at roughly 1.8 m.y. BP.