Torso morphology and locomotion in Proconsul nyanzae

Abstract

A new partial skeleton of Proconsul nyanzae from Mfangano Island, Kenya (KNM-MW 13142) includes five lumbar vertebrae, a partial sacrum, and nearly complete hipbone. Until recently, little was known of the axial and pelvic skeletons of Proconsul, or any early Miocene hominoid. Because torso morphology directly reflects locomotor behavior, these elements provide important new information about posture and locomotion of P. nyanzae. Two basic patterns of locomotor behavior and corresponding torso morphology exist among extant anthropoids. Monkeys have long, flexible spines with powerful epaxial muscles and mediolaterally narrow thoraces. This morphology represents a response to the mechanical requirements of habitual pronograde quadrupedalism. In contrast, hominoids, 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 lower back during forelimb-dominated arboreal locomotion. KNM-MW 13142 had craniocaudally elongate vertebral bodies, and probably six lumbar vertebrae, reflecting a long, flexible vertebral column. The narrow, laterally facing iliac blades of KNM-MW 13142 imply the presence of a mediolaterally narrow, dorsoventrally deep thorax. Its wide iliac tuberosities, ventrally located lumbar transverse processes, and distinct accessory processes suggest that Proconsul nyanzae also had strap-like epaxial muscles similar to those characterizing most monkeys. Axial and pelvic morphology of KNM-MW 13142 indicate that P. nyanzae had not undergone an ape-like rearrangement of its torso to adapt to forelimb-dominated arboreality. Instead, P. nyanzae probably retained a more primitive pattern of pronograde quadrupedalism. This morphology indicates that the extant hominoid pattern of torso anatomy arose subsequent to the establishment of the hominid clade.

Etiology of lumbar lordosis and its pathophysiology: a review of the evolution of lumbar lordosis, and the mechanics and biology of lumbar degeneration

“…128 The short lumbar spines of great apes are very stiff and have limited flexion. 201 This differential evolution of human and old world primate lumbar spines suggests a functional purpose for 5 lumbar vertebrae in humans, not an evolutionary failure.…”

Gibbons and hominoid ancestry

“…The conclusion to be drawn from the morphology of proconsulids is that they were arboreal climbers, moving on the tops of branches, but they were not habitual leapers rather moved slowly and powerfully in the trees. They were mainly fruit eaters with body sizes varying from 9-11 kg to 63-83 kg, from siamang size to larger than chimpanzees, and some degree of terrestrial activity is indicated, particularly for the larger species, which were as big as chimpanzees or even bigger (Le Gros Clark and Leakey, 1951;Napier and Davis, 1959;Napier, 1960;Andrews, 1978Andrews, , 1992Walker et al, , 1993Rose, 1983Rose, , 1984Beard et al, 1986;Gebo et al, 1988;Rafferty, 1988;Lewis, 1989;Teaford, 1988, 1989;Ward, 1993;Begun et al, 1994;Teaford, 1994;Rafferty et al, 1995;Ward et al, 1995;Harrison, 2002;Gebo et al, 2009). Primates at the upper end of the size range and living in woodland (non-forest) environments, must have been partly terrestrial, as in chimpanzees and gorillas today, for they were too large to move easily between arboreal pathways.…”

“…Clearly, primates of this size, living in relatively open canopy woodlands, would have had to spend part of their time on the ground. The thick enamel of their teeth suggest a harder, coarser fruit and nut diet compared with proconsulids (Tekkaya, 1974;Alpagut et al, 1990Alpagut et al, , 1996Teaford, 1988Teaford, , 1991Harrison, 1992;McCrossin and Benefit, 1997;McCrossin et al, 1998;Nakatsukasa et al, 1998Nakatsukasa et al, , 2007Begun and Güleç, 1998;King et al, 1999;Ishida et al, 1999Ishida et al, , 2004Ward, 1993;Ward et al, 1995;Kelley et al, 2000Kelley et al, , 2002Kelley et al, , 2008Kelley, 2002Kelley, , 2008Ungar, 2007;Ersoy et al, 2008;Nakatsukasa, 2008).…”

The zoogeographic and phylogenetic relationships of early catarrhine primates in Asia

“…Recently published 40 Ar/ 39 Ar dates indicate an age of 20.6 Ma (Gebo et al, 1997), although Pickford (1998) and Pickford et al (1999Pickford et al ( , 2003 claim that Moroto may be younger, possibly late early Miocene (~17.0-17.5 Ma) or early middle Miocene, based on faunal correlations. Morotopithecus is recognized as a stem hominoid based on the presence of synapomorphies of the postcranium (particularly the lumbar vertebrae) that link it with extant hominoids (Ward, 1993;Sanders and Bodenbender, 1994;Gebo et al, 1997; and Benefit, 1994;Ward et al, 1999;Ward and Duren, 2002). During MN 5 and basal MN 6 (~14-17 Ma), Griphopithecus, a primitive hominoid similar in dental morphology and probably closely related to Equatorius, expanded its range into Eurasia, soon after the arrival of pliopithecids (Andrews et al, 1996;Heizmann and Begun, 2001).…”