Author(s)

Naoko Miyakawa^1*, Toshiya Kishiro², Yoshihiro Fujise³, Gen Nakamura¹, Hidehiro Kato¹

¹Laboratory of Cetacean Biology, Tokyo University of Marine Science and Technology, Tokyo, Japan.
²National Research Institute of Far Seas Fisheries, Yokohama, Japan.
³Institute of Cetacean Research, Tokyo, Japan.

Little is known about the morphology of the pelvic girdle of modern cetaceans, although many species have a vestigial pelvis (pelvic bone) and part of the hind limb bones inside the body. Previous studies have focused almost exclusively on hard tissues as well, despite the fact that the bones are comprised of cartilaginous tissue, especially in the case of femur. In the present study, we characterized the pelvic bones and searched for vestigial femurs among 43 North Pacific common minke whales (Balaenoptera acutorostrata), all of which were sexually mature individuals. The shape of the pelvic bones clearly differs depending on sex. Specifically, the pelvic bones of females were flat, but those of adult males consist of two types: one with a twisted caudal portion (Twisted type) and the other with a thickened caudal portion (Hypertrophied type). Those pelvic bone features in male are found only among North Pacific common minke whales. 98% of the individuals in this study had vestigial femur. The presence rate of vestigial femur may differ by subspecies. The shape of the pelvic and hind limb bones of modern cetaceans may vary between species and probably by region, at least at the Ocean basin scale.

Pelvic Bone, Femur, Cartilage, Common Minke Whale, Sexual Dimorphism

Miyakawa, N. , Kishiro, T. , Fujise, Y. , Nakamura, G. and Kato, H. (2016) Sexual Dimorphism in Pelvic Bone Shape of the North Pacific Common Minke Whales (Balaenoptera acutorostrata). Open Journal of Animal Sciences, 6, 131-136. doi: 10.4236/ojas.2016.62016.