Is the Clavicle of Apes Long? An Investigation of Clavicular Length in Relation to Body Mass and Upper Thoracic Width
- 246 Downloads
An elongated clavicle is one of the distinct features of apes and humans. It plays an important role in providing mobility as well as stability for the shoulder joints. The relative length of the clavicle is an especially important factor in limiting the range of shoulder joint excursion. It is said that among primates, Asian apes, i.e., gibbons and orang-utans, have very long clavicles. At the same time, they also have a wide upper thoracic cage, which may diminish the effective length of the clavicle. To clarify the length of the clavicle in apes, from the standpoint of the functional anatomy of the shoulder girdle, we examined clavicular length in 15 anthropoid species exhibiting various positional behaviors. The results confirm that clavicle length in Asian apes is long, and chimpanzees have a short clavicle like that of Old and New World monkeys, when scaled to body mass. The clavicular length of chimpanzees, however, is intermediate between Old World monkeys and Asian apes when scaled against thoracic width. Therefore, living apes can be grouped together, albeit just barely, by possession of a relatively long clavicle for their thoracic cage size. Interestingly, New World monkeys tend to exhibit a longer clavicle than Old World monkeys of equivalent body mass or thoracic cage width. Although it is unclear whether the ancestral condition of clavicular length in anthropoids was similar to that of living Old or New World monkeys, an elongation of clavicle was an important step toward evolution of the modern body plan of hominoids.
Keywordsarboreal adaptation clavicle shoulder girdle shoulder mobility thoracic morphology
We thank Dr. Todd C. Rae, Prof. Dr. Yuzuru Hamada, and Dr. Eishi Hirasaki for their encouragement and patience, which helped make our contribution to this special issue possible. The insightful comments from the 2 anonymous reviewers and the grammatical corrections by Dr. Todd C. Rae greatly improved this manuscript. We thank Prof. Dr. Christoph P. E. Zollikofer and Dr. Marcia Ponce de León, Anthropological Institute, University of Zürich; Dr. Richard Kraft, the Bavarian State Collection of Zoology, München; Dr. Kunimatsu Yutaka, Primate Research Institute, Kyoto University; and Dr. Takano Tomo, Japan Monkey Centre, for allowing us access to specimens. This work was supported by JSPS core-to-core program HOPE, a Grant for the Biodiversity Research of the 21st Century COE (A14), and by the Cooperation Research Program of the Primate Research Institute, Kyoto University.
- Chan, L. K. (1997). Thoracic shape and shoulder biomechanics in primates. Ph.D. dissertation, Duke University, Durham, NC.Google Scholar
- Grand, T. I. (1984). Motion economy within the canopy: Four strategies for mobility. In P. S. Rodman & J. G. H. Cant (Eds.), Adaptations for foraging in nonhuman primates (pp. 54–72). New York: Columbia University Press.Google Scholar
- Jungers, W. L. (1984). Scaling of the hominoid locomotor skeleton with special reference to lesser apes. In H. Preuschoft, D. J. Chivers, W. Y. Brockelman, & N. Creel (Eds.), The lesser apes: Evolutionary and behavioral biology (pp. 146–169). Edinburgh: Edinburgh University Press.Google Scholar
- Preuschoft, H., Schmidt, M., Hayama, S., & Okada, M. (2003). The influence of three-dimensional movements of the forelimb on the shape of the thorax and its importance for erect body posture. Courier Forschungsinstitut Senckenberg, 243, 9–24.Google Scholar
- Schultz, A. H. (1961). Vertebral column and thorax. Primatologia, 4, 1–66.Google Scholar
- Schultz, A. H. (1968). The recent hominoid primates. In S. L. Washburn & P. C. Jay (Eds.), Perspectives on human evolution (Vol. 1, pp. 122–195). New York: Holt, Rinehart and Winston.Google Scholar