Presence of an interparietal bone and morphological variation in the vertex of the skull in North Pacific common minke whale

Abstract

The vertex of the skull is regarded as one of the most important categorical traits in taxonomy in baleen whales. However the previously reported species-specific characteristics for the North Pacific common minke whale, were based on only a very limited number of specimens Therefore, we aimed to assess the efficacy of these morphological characteristics as categorical traits, based on specimens of North Pacific common minke whales collected from the JARPNII survey（n =106）. The frontal border of the nasal bones, as well as the positional relationship of the end of premaxilla and the nasal bones, were varied widely by individual, indicating that these traits are not appropriate for species classification. However, the end of the maxilla was located posteriorly to the end of the premaxilla and the nasal bones in all whales surveyed. Therefore, we conclude that this characteristics can serve as universal species-specific morphological characteristics for the North Pacific common minke whales. Furthermore, we found an interparietal bone in all whales surveyed. This bone has been regarded as one of the specific character of “dwarf” minke and have not been reported from any common minke whales in the North Pacific.