Structure and scaling of the lumbar vertebrae in African bovids (Mammalia: Artiodactyla)

Authors

  • A. P. Halpert,

    1. Department of Organismic and Evolutionary Biology and Museum of Comparative Zoology, Harvard University, Cambridge, Massachusetts 02138, USA
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  • F. A. Jenkins Jr,

    Corresponding author
    1. Department of Organismic and Evolutionary Biology and Museum of Comparative Zoology, Harvard University, Cambridge, Massachusetts 02138, USA
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  • H. Franks

    1. Department of Organismic and Evolutionary Biology and Museum of Comparative Zoology, Harvard University, Cambridge, Massachusetts 02138, USA
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Department of Organismic and Evolutionary Biology and Museum of Comparative Zoology, Harvard University, Cambridge, Massachusetts 02138, USA

Abstract

The structure and dimensions of the lumbar vertebrae from 18 genera of African bovids (with a body weight range of 4–900 kg) were studied with reference to allometric and biomechanical factors. Centrum height scales with body weight according to McMahon's elastic similarity theory, but centrum width scales geometrically with body weight. Thus, the dimensions of bones need not scale according to a single principle. Transverse process orientation, as measured in two planes, varies allometrically with body weight; this trend may reflect size-related differences in abdominal girth and spinal musculature. Bovids exhibit decreasing lumbar mobility in the sagittal plane with increasing body size, a phenomenon related to an increase in centrum height and the appearance of interlocking mechanisms (postzygapophysial ridges and prezygapophysial labra). Geometric scaling of centrum width and zygapophysial curvature is evidence that lateral flexion of the spine occurs throughout the family. In all taxa examined, the last lumbar vertebra exhibits an absolutely wider centrum and straight postzygapophyses, thus reducing lateral mobility at the lumbosacral joint. In heavier bovids, the observed restriction of lumbar flexion and extension to the lumbosacral joint is a consequence of the distribution of the shapes of the centra and the interlocking mechanisms of the zygapophyses.

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