TORSO MORPHOLOGY AND LOCOMOTION IN PROCONSUL-NYANZAE

A new partial skeleton of Proconsul nyanzae from Mfangano Island, Keny a (KNM-MW 13142) includes five lumbar vertebrae, a partial sacrum, and nearly complete hipbone. Until recently, little was known of the axia l and pelvic skeletons of Proconsul, or any early Miocene hominoid. Be cause torso morphology directly reflects locomotor behavior, these ele ments provide important new information about posture and locomotion o f P. nyanzae. Two basic patterns of locomotor behavior and correspondi ng torso morphology exist among extant anthropoids. Monkeys have long, flexible spines with powerful epaxial muscles and mediolaterally narr ow thoraces. This morphology represents a response to the mechanical r equirements of habitual pronograde quadrupedalism. In contrast, homino ids, particularly great apes, have shorter, stiffer spines and broader torsos than do monkeys. The hominoid pattern reflects an emphasis on forelimb abduction-adduction, and on stability and control of the lowe r back during forelimb-dominated arboreal locomotion. KNM-MW 13142 had craniocaudally elongate vertebral bodies, and probably six lumbar ver tebrae, reflecting a long, flexible vertebral column. The narrow, late rally facing iliac blades of KNM-MW 13142 imply the presence of a medi olaterally narrow, dorsoventrally deep thorax. Its wide iliac tuberosi ties, ventrally located lumbar transverse processes, and distinct acce ssory processes suggest that Proconsul nyanzae also had strap-like epa xial muscles similar to those characterizing most monkeys. Axial and p elvic morphology of KNM-MW 13142 indicate that P. nyanzae had not unde rgone an ape-like rearrangement of its torso to adapt to forelimb-domi nated arboreality. Instead, P. nyanzae probably retained a more primit ive pattern of pronograde quadrupedalism. This morphology indicates th at the extant hominoid pattern of torso anatomy arose subsequent to th e establishment of the hominid clade. (C) 1993 Wiley-Liss, Inc.