Development of the Laryngeal Air Sac in Chimpanzees |
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Authors: | Takeshi Nishimura Akichika Mikami Juri Suzuki Tetsuro Matsuzawa |
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Institution: | (1) Laboratory of Physical Anthropology, Department of Zoology, Graduate School of Science, Kyoto University, Kitashirakawa Oiwake-cho, Sakyo, Kyoto 606–8502, Japan;(2) Primate Research Institute, Kyoto University, 41 Kanrin, Inuyama, Aichi 484–8506, Japan |
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Abstract: | Though many nonhuman primates possess a laryngeal sac, the great apes are unique in their great size. Though an enlarged sac
probably arose in their common ancestor, its functional adaptations remain a matter of debate. Its development in extant great
apes is likely to provide valuable information to clarify the issue. We used magnetic resonance imaging to examine the development
of the laryngeal sac in 3 living chimpanzees, age 4 mo–5 yr, and identified 2 distinct growth phases of the sac. A gradual
growth of the sac in early infancy results in a configuration so that it occupies the ventral region of the neck; many adult
nonhominoid primates having a sac show the configuration. The subsequent rapid expansion of the sac in late infancy causes
the final configuration in chimpanzees, wherein the sac expands into the pectoral, clavicular, and axillary regions. The latter
phase possibly arose at latest in the last common ancestor of extant great apes and contributed to the evolution of the enlarged
sac, despite the later evolutionary diversification in adult sac anatomy and growth. As many studies have advocated, the enlarged
sac probably plays a role in vocalization in adults. However, physiological modifications in the laryngeal region during infancy
are likely to provide valuable information to evaluate the functional adaptations of the enlarged sac in the great apes. |
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Keywords: | magnetic resonance imaging Pan troglodytes ventricular sac vocalization |
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