On the vertex of the dorsal skull the premaxillary bone extends forward of the nasal and frontal bones. Separates from Berardius and Ziphius.
A sulcus (groove) running along the middle of the combined surfaces of the nasal bones so depresses their combined middle that it is the lateral portion of each nasal bone that reaches farthest forward on the vertex. Separates from Tasmacetus and Indopacetus.
When the skull is upright and the long axis of the anterior half of the beak is horizontal, a horizontal plane transecting the summit of either maxillary prominence passes well above the mesethmoid bone. Separates from Berardius, Ziphius, Tasmacetus, Indopacetus, and Mesoplodon.
Maxillary crests do not extend posterior to the external nares and become confluent with the occipital crests. Separates from Hyperoodon planifrons.