Australopithecus sediba Hand Demonstrates Mosaic Evolution of Locomotor and Manipulative Abilities

Abstract

Hand bones from a single individual with a clear taxonomic affiliation are scarce in the hominin fossil record, which has hampered understanding the evolution of manipulative abilities in hominins. Here we describe and analyze a nearly complete wrist and hand of an adult female [Malapa Hominin 2 (MH2)] Australopithecus sediba from Malapa, South Africa (1.977 million years ago). The hand presents a suite of Australopithecus-like features, such as a strong flexor apparatus associated with arboreal locomotion, and Homo-like features, such as a long thumb and short fingers associated with precision gripping and possibly stone tool production. Comparisons to other fossil hominins suggest that there were at least two distinct hand morphotypes around the Plio-Pleistocene transition. The MH2 fossils suggest that Au. sediba may represent a basal condition associated with early stone tool use and production.

Primate origins, human origins, and the end of higher taxa

“…[118][119][120] But there is conclusive evidence that a lot of supposedly human features were acquired in parallel in different lineages of Pleistocene hominins. Probable parallelisms include the increased basicranial flexion and other basicranial apomorphies seen in late robust Australopithecus species 53:194 ; molar reduction and humanlike changes in the pelvis and hand in A. sediba [121][122][123] ; brain enlargement in some habilines (KNM-ER 1470) and facial and dental reduction in others (KNM-ER 1813); and so on. If our family tree within the genus Homo is as bushy and speciose as some like to think, 124 then parallel evolution was also rampant throughout the later Pleistocene, with brain enlargement and correlated cranial changes taking place independently between 1.0 and 0.3 Mya in the local Homo populations of Africa, Java (Ngandong), Europe (Neandertals), and perhaps in other isolated demes.…”

The 2014 ABJS Nicolas Andry Award: The Puzzle of the Thumb: Mobility, Stability, and Demands in Opposition

“…Primate comparative anatomy and the scant evidence from early hominins suggest the human saddle joint affords more motion with its shallower, looser design and robust complement of intrinsic muscles [1,2,52,56,69,102]. CMC arthritis in great apes and other primates is unknown, although other wrist arthritis is common in knuckle-bearing gorillas [93].…”

Early Pleistocene third metacarpal from Kenya and the evolution of modern human-like hand morphology

“…1A) is another distinctive feature of the modern human/Neandertal hand that is absent in all apes and other nonhuman primates, as well as Pliocene and Early Pleistocene hominins (11,14,16,(21)(22)(23)(24)(25)(26)(27). The dorsal extension of bone seen in a single specimen of Au.…”

“…Australopithecus afarensis, Australopithecus africanus, and Australopithecus sediba also have short fingers (9, 11-14) (see ref. 15 for alternative view regarding A. afarensis), but with a conspicuously gracile pollical metacarpal (13)(14)(15)(16). Robust thumb metacarpals are associated with relatively large and less-curved first carpometacarpal joint surfaces, facilitating the accommodation of large axial loads generated during strong precision and precision-pinch grasps (9,(17)(18)(19)(20).…”