Morphological study of the anthropoid thoracic cage: scaling of thoracic width and an analysis of rib curvature |
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Authors: | Miyuki Kagaya Naomichi Ogihara Masato Nakatsukasa |
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Institution: | (1) Laboratory of Physical Anthropology, Department of Zoology, Graduate School of Science, Kyoto University, Sakyo, Kyoto 606-8502, Japan |
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Abstract: | While a relatively broad thorax and strongly curved ribs are widely regarded as common features of living hominoids, few studies
have quantitatively examined these traits by methods other than calculating the chest index. The present study aims to quantify
variations in thoracic cage morphology for living anthropoids. The odd-numbered ribs (first to eleventh) were articulated
with the corresponding vertebrae and the cranial and lateral views subsequently photographed. Rib profiles were digitized
in both views and line-fitted by a Bézier curve to create a three-dimensional morphological data set. When thoracic cage width
was scaled against body mass, Hylobates (and possibly Pongo) plotted above non-hominoid anthropoids at almost all rib levels, while Pan did not differ from non-hominoid anthropoids. The overall pattern of the normalized thoracic width differed between Hylobates and other hominoids. In Hylobates, an upward convex curve was seen between the first and seventh ribs while a more linear pattern was observed in Pan and Pongo. This result quantitatively confirmed that the barrel-shaped thoracic cage in Hylobates can be distinguished from the funnel-shaped form in other hominoids. Conversely, all hominoids shared two distinct features
in the upper half-thorax: (1) a pronounced dorsal protrusion of the proximal part of the rib in accordance with ventral displacement
of the thoracic spine and (2) a relatively medially projecting sternal end. Although these features are likely to provide
some mechanical advantage in orthograde and/or suspensory positional behaviors, they were barely present in the suspensory
Ateles.
An erratum to this article can be found at |
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Keywords: | Anthropoid Hominoid Rib curvature Scaling Thoracic cage |
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