COMPARATIVE MORPHOMETRIC STUDY OF THE AUSTRALOPITHECINE VERTEBRAL SERIES STW-H8 H41/

Lower spinal structure correlates well with positional behavior among mammals. Nonetheless, the functional morphology of the axial postcrani a of australopithecines has received less attention than their appendi cular skeletons. This paper presents a detailed description and compar ative morphometric analysis of the australopithecine thoracolumbar ver tebral series Stw-H8/H41, and examines spinal mechanics in early homin ids. Stw-H8/H41 is an important specimen, as the australopithecine ver tebral sample is small, and vertebral series are more useful than isol ated elements for the interpretation of spinal function. Results of th e study support the interpretation that australopithecine species are highly sexually dimorphic. The study also reveals a considerable amoun t of morphometric variation other than size among australopithecine ve rtebrae, though the sample is too small and incomplete to ascertain wh ether this indicates significant interspecific differences in spinal f unction. Most importantly, structural and metric observations confirm that the morphology of the lower spine in australopithecines has no mo dern analogue in its entirety. Aspects of zygapophyseal structure, num erical composition of the lumbar region, and centrum wedging suggest t hat the australopithecine vertebral column was adapted to human-like i ntrinsic lumbar lordosis and stable balance of the trunk over the pelv is in sustained bipedal locomotion., However, relative centrum size in australopithecines indicates that either they had a different mechani sm for channeling vertical forces through the vertebral column than hu mans, or differed behaviorally from humans in ways that produced small er increments of compression across their centra. These findings have important implications for hypotheses of australopithecine positional behavior, and demonstrate that larger samples and more complete verteb ral series are needed to improve our understanding of australopithecin e spinal function. (C) 1998 Academic Press Limited.