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1 September 2013 Relative Skull Growth of the Sperm Whale, Physeter macrocephalus, with a Note of Sexual Dimorphism
Gen Nakamura, Ryoko Zenitani, Hidehiro Kato
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By using skulls of sperm whales (Physeter macrocephalus), we analyzed the relative growth of skull length in relation to that of body length. We also analyzed the growth of various parts of the skull in relation to skull length. We used data of 3 males and 1 female collected off the coast of Japan and those of 4 males reported previously. In males, the proportion of skull length to body length increased with growth from 26% (body length, 10 m) to 32% (body length, over 16 m, most of which were considered as physically mature). In contrast, the proportion reached less than 25% in the physically mature female. In males, the relative length of the rostrum and the mandible to skull length increased with growth, and the posterior margin of the occipital bone tended to protrude posteriorly. This posterior protrusion could be considered as a secondary sexual dimorphism observed only in the skull of physically mature males. These characteristics would be associated with sex differences and deep diving as well as to the life style and breeding strategy of sperm whales, a species in which males physically compete for breeding rights.

© The Mammal Society of Japan
Gen Nakamura, Ryoko Zenitani, and Hidehiro Kato "Relative Skull Growth of the Sperm Whale, Physeter macrocephalus, with a Note of Sexual Dimorphism," Mammal Study 38(3), 177-186, (1 September 2013).
Received: 6 November 2012; Accepted: 1 May 2013; Published: 1 September 2013
Physeter macrocephalus
sexual dimorphism
Sperm Whale
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