Figure 1.

Size and proportions of the Oreopithecus hand. (a) Relation between hand length (carpals, metacarpals, and phalanges of the third digit) and body weight in anthropoid primates (log10; body mass, refs. 14 and 26). Hands of orthograde anthropoids (apes) are considerably longer than those of pronograde anthropoids because a large friction surface is needed to secure a firm hold during vertical climbing and hanging from branches. Both Miocene hominoids that yielded hand remains show the expected proportions: the pronograde Proconsul (P) has relatively short hands whereas the orthograde Dryopithecus (D) has long hands, as in extant apes. Four orthograde genera, however, do not follow this rule, as they have shorter hands than expected for their body weight: in Gorilla (G), this is attributable to the great body weight and the primarily terrestrial quadrupedal locomotion (22) whereas in Homo (H) it is attributable to the shift from a mainly locomotor to a more manipulative use of the hands. The reduction of hand length in Oreopithecus (O) presumably occurred for similar reasons as in hominids (see discussion in the text). (b) Relation between hand length (carpals, metacarpals, and phalanges of the third digit) and humerus length in anthropoid primates, Oreopithecus, and other fossil anthropoids. T, Theropithecus; Pa, Papio; Pl, Pliopithecus.