Figure 2.

(a) The length of the proximal phalanges of the thumb set against the length of the proximal phalanges of the index finger of anthropoids, for the two complete hands of Oreopithecus (BA#140 and IGF 11778) and other forms. In an allometric context, the platyrhine condition (solid line) is likely to be primitive for anthropoids while there are two derived characters: the relatively long first phalanx of the thumb in Papio, Theropithecus, Homo, and Oreopithecus; and the relatively short proximal thumb phalanx in colobinae, apes, and, especially, Pongo. The Proconsul specimens considered are KNM-RU 2036 and the subadult individual I from the channel deposit at Kaswanga Primate Site (27). (Lph 1/2, length of the first phalange of the second ray; Lph 1/1, length of the first phalange of the thumb.) (b) Relation between thumb (pollex) length (metacarpal 1 and phalanges) and index finger length (metacarpal 2 and phalanges; log10). Colobines, hylobatids, chimps, and gorillas show an allometric relationship. Only Pongo falls above the regression line, with a relatively very long index finger in relation to its short thumb. Oreopithecus (BA#140), however, shows the same proportions as A. afarensis (A:AL#333) and Homo sapiens. The length of the A. afarenis thumb is reconstructed from the known lengths of metacarpal 1 and proximal phalanx and with a length for the distal phalanx estimated at 20.1 mm (based on the relationship between the lengths of the mc 1 and distal phalanx in modern humans).