Fossil primate hands: A review and an evolutionary inquiry emphasizing early forms

Abstract

The paleontological evidence pertaining to the evolution of the modern diversity in structure and function of primate hands is reviewed. A reconstructed digit of Plesiadapis shows characters and functional capacities typical of an arboreal way of life. In euprimates, we describe the strepsirhine morphotype hand, characterized by a relatively high degree of pollical divergence, features of the ulnocarpal articulation that imply an enhanced capacity for ulnar deviation, and relatively long digits; this hand is specialized for grasping. Hand remains of Smilodectes, Adapis and a Messel adapiform reveal a remarkable diversity in carpal structure achieved in these Eocene adapiforms, due to differing locomotor evolutionary pathways. The subfossil lemuriforms Megaladapis and Palaeopropithecus both show stereotyped (but different) grasping capabilities. The simiiform morphotype hand combines a relatively low degree of pollical divergence, features of the ulnocarpal articulation that imply a limited capacity for ulnar deviation, and relatively long metacarpals and short digits. This type of hand anatomy is mechanically well-suited to arboreal palmigrade quadrupedalism. The hands of Pliopithecus and Mesopithecus are generally monkey-like. Oreopithecus' hand fits with its presumed suspensory habits. The hand of Proconsul suggests palmigrade quadrupedalism and climbing. Australopithecus afarensis' hand remains primarily a branch-grasping organ, with indications of enhanced manipulatory abilities. Homo habilis and Paranthropus robustus illustrate two lines of increased tool-use abilities. The euprimate morphotype hand was elongated, had a short carpus and limited mobility, but the corresponding locomotor mode remains speculative. Considerations on hand evolution in some living primate groups are included in the final summary of hand evolution in primates. © 1991 Editrice II Sedicesimo.