On the vertex of the dorsal skull the nasal bone extends forward of the premaxillary and frontal bones. Separates from Indopacetus, Hyperoodon, Mesoplodon, and Tasmacetus.
When the posterior aspect of the skull is viewed from a point aligned with the long axis of the rostrum, the profile of the vertex projects above the supraoccipital as a slightly asymmetrical block with sheer sides. Separates from Ziphius.Available literature documenting diagnostic cranial differences between B. bairdii and B. arnuxii are not yet available. The geographic separation between B. bairdii in the Northern Hemisphere and B. arnuxii in the Southern Hemisphere can be used differentiate the two species.