A Reconsideration of the Endocast of Proconsul africanus

Abstract

Description of the cortical sulcal pattern of the early Miocene Proconsul africanus skull (BMNH M 32363) from Rusinga Island, Kenya has had a checkered history. Le Gros Clark and Leakey (1951) described the sulcal markings on the endocranial aspect of the frontal and parietal regions of the right side of the Proconsul skull. They suggested that Proconsul had a relatively small frontal lobe and a sulcal pattern that appeared to be cercopithecoid-like, rather than hominoid-like. Radinsky (1974) redescribed the sulcal pattern of the same specimen from an endocast that extended slightly further caudally than the area described by Le Gros Clark and Leakey (1951). Radinsky noted that the endocast resembled the brains of modern gibbons more than those of cercopithecoids and concluded that the Proconsul endocast therefore represented a hominoid rather than a cercopithecoid sulcal pattern. This latter assessment was based on comparison of the Proconsul sulcal pattern with sulcal patterns from a small number of cercopithecoid and gibbon specimens. Since then, large numbers of cercopithecoid (Falk, 1978a,b; Radinsky, 1979), ceboid (Falk, 1980b, 1981), pongid (Radinsky, 1975, 1977, 1979; Falk, 1980a), and hominid (Falk, 1979b, 1980a, 1980c; Radinsky, 1979) endocasts and/or brains have been studied and cladistic analysis has been applied to the study of sulcal patterns (Falk, 1979a). The purpose of this chapter is to redescribe the partial endocast of Proconsul (BMNH M 32363) a third time, in light of recent findings, and to discuss the implications of its sulcal pattern for primate brain evolution.