2008 Volume 0 Issue 18 Pages 1-7
The U-shaped rostrum is the main characteristic feature in the skull of the blue whale, Balaenoptera musculus. In his preceding study on balaenopterid mandibles, one of the authors, Oishi, indicated that the morphology of the mandible has a close relevancy to that of the rostrum, as follows. The mandible of the blue whale has unique characteristics such as the condylar region rotating inward and the coronoid process extending upward when the mandible is laid on the horizontal floor. In contrast, the Antarctic minke whale, Balaenoptera bonaerensis, has a mandible showing a non-rotating condylar region and the coronoid process extending upward and outward. The difference between the mandibles of the blue whale and the Antarctic minke whale corresponds with rostral morphology. The U-shaped rostrum of the blue whale requires no inward rotation of the mandible at the long axis, however the mandible of the Antarctic minke whale rotates inward when its mouth is closed so that the hiatus between the mandible and the V-shaped rostrum is minimized. In this situation, the condylar region of the mandible of the Antarctic minke whale rotates inward. In other words, the state of articulation in the condylar region is equivalent in both the blue and Antarctic minke whales when the mouths are closed. In this study, the authors validated the evidence noted above by using 3DCG software. The results of our 3D simulations show the validity of the preceding study by one of the authors. Furthermore, we newly recognized the weak inward rotation of the mandible when the mouth of the blue whale is closed. 3D computer models enable us to conduct virtual tests on enormous materials such as whale skulls.