Morphology of the male teeth is one of the major diagnostic characters for the species identification in genus Mesoplodon. Among four species of the genus known from the Japanese waters, strandings of Stejneger's beaked whale ( M. stejnegeri ) and Ginkgo-toothed beaked whale ( M. ginkgodens ) were reported from the Sea of Japan. The present research deals with the shape change of tooth found in M. stejnegeri according to the age. Almost conical neonate teeth change into tall and thick spatular like tusks. Among 32 specimens observed, 5 stages are recognized in their shape: Stage 1, unisexual, almost conical tooth with tall triangular profile; Stage 2, somewhat flattened triangular tooth also unisexual; Stage 3, ovoid to chestnut shape and found only in male individuals; Stage 4, tall and large tooth or tusk almost spatular shaped and found also in males; Stage 5, basically similar to the Shape 4 but with an incision at the anterior edge of the tooth neck. On the basis of their frequencies, the shape change from stage 3 to 4 can be very rapid. Species diagnosis of individuals with Stage 3 teeth should be done carefully since the tooth profile is similar to those of M. ginkgodens. Further analyses are expected with more data of age determination, sexual maturity, mesorostral ossification and scarring.

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This present study discusses a custom of sharing in dolphin ‟fishing” in the Jomon period, mainly on the basis of the butchery marks in the case of an articulated vertebrae of a dolphin, excavated from the Mawaki site. The example is of a bottlenose dolphin size and consists of 15 vertebrae from lumbar to caudal, probably L10 to Ca9, the total length of about 71 cm. No.9 (Cal) has 46.6 mm length of corpus vertebrae, 60.8 mm breadth of facies terminalis caudalis and 59.0 mm height of facies terminalis caudalis. No.1 (Ca9) shows cut marks in the direction of the cranial-caudal line on the caudal base of left and right processus transversi. Scratch injuries are found in the direction of the cranial-caudal line on the dorsal surface of the left processus transversi of No.2 (Ca8) to No.5 (Ca5) and also on the ventral surface of the right processus transversus of No.7 (Ca3). Cut or scratch injuries are found in the direction of the dorsal-vental line on the cranial side of left processus transversus. I regard the cut marks on No.1 (Ca9) as incisions caused by dividing articulated vertebrae covered with strong ligaments into sections, though it is a hard task, for fishermen sharing a dolphin not only within their own settlement but also with other settlements.

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