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Rib orientation and implications for orthograde positional behavior in nonhuman anthropoids
Miyuki Kagaya1, Naomichi Ogihara, Masato Nakatsukasa
1Laboratory of Physical Anthropology, Department of Zoology, Graduate School of Science, Kyoto University, Sakyo, Kyoto, Japan. kagaya@mnhn.fr
Primates; Journal of Primatology
|June 17, 2009
Summary
Hominoids, including humans, show stronger caudal obliquity in lower ribs than monkeys. This rib orientation may relate to suspensory and orthograde behaviors in primates.
Area of Science:
- Primate anatomy
- Comparative biomechanics
- Evolutionary anthropology
Background:
- Strong caudal obliquity of lower ribs is a proposed hominoid and Ateles characteristic.
- This obliquity aids in scapular stability during forelimb propulsion via serratus anterior muscles.
Purpose of the Study:
- To investigate the orientation of odd-numbered ribs in nonhuman anthropoids.
- To compare rib obliquity patterns between hominoids and monkeys (Old World and New World).
Main Methods:
- Examination of rib orientation in lateral view.
- Analysis of fifteen remounted thoracic skeletons of nonhuman anthropoids.
Main Results:
- Hominoids display more pronounced caudal obliquity in the seventh and ninth ribs than monkeys.
- Maximum thoracic cage width, near serratus anterior attachment, is more caudal in Hylobates and Pongo.
- Rib obliquity patterns are similar between Old and New World monkeys, including Ateles.
Conclusions:
- Pronounced lower rib obliquity is characteristic of hominoids, differing from monkeys.
- This feature may be linked to both suspensory and orthograde positional behaviors in primates.
- Further research is needed to fully understand the functional implications of rib obliquity.
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