Abstract
Strong caudal obliquity of the lower ribs is one of the assumed characteristics of the thoracic region in hominoids and Ateles. Strong caudal obliquity keeps the scapula of the weight-bearing forelimb on the dorsal surface of the trunk via the serratus anterior muscles during propulsion (Stern et al. 1980). We examined the orientation of odd-numbered ribs in lateral view in remounted thoracic skeletons of fifteen nonhuman anthropoids. Hominoids exhibit pronounced caudal obliquity in the seventh and ninth ribs compared to Old and New World monkeys. The position of the maximum thoracic cage width, which approximates the attachment of the serratus anterior muscle, is more caudally located in Hylobates and Pongo. The overall pattern of rib obliquity is generally similar between New and Old World monkeys, including Ateles. Perhaps not only forelimb suspensory behavior but also various orthograde positional behaviors are related to the strong obliquity of the lower ribs; however, further investigation is necessary.
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Acknowledgments
We are grateful to Dr. Kunimatsu Yutaka of the Primate Research Institute, Kyoto University, Japan; Dr. Takano Tomo of the Japan Monkey Centre; Dr. Richard Kraft of the The Bavarian State Collection of Zoology, München, Germany; and Prof. Dr. Christoph P.E. Zollikofer and Dr. Marcia S. Ponce de León of the University of Zürich, Switzerland, for their courtesy in allowing access to specimens. Valuable suggestions regarding the manuscript were also made by Prof. Dr. Michael Rose and two anonymous reviewers. This work was supported by JSPS-HOPE, a Grant for Biodiversity Research from the Twenty-First Century COE (A14), the Global COE Program “Formation of a Strategic Base for Biodiversity and Evolutionary Research: from Genome to Ecosystem,” a Grant-in-Aid for Scientific Research on Priority Areas, “Emergence of Adaptive Motor Function Through Interaction between Body, Brain and Environment,” from the Japanese Ministry of Education, Culture, Sports, Science and Technology, and by the Cooperation Research Program of the Primate Research Institute, Kyoto University.
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Kagaya, M., Ogihara, N. & Nakatsukasa, M. Rib orientation and implications for orthograde positional behavior in nonhuman anthropoids. Primates 50, 305–310 (2009). https://doi.org/10.1007/s10329-009-0147-0
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DOI: https://doi.org/10.1007/s10329-009-0147-0