Mesoplodont Whales

Stranding Distribution There are abundant records from the cold temperate waters of the southern oceans between 30oS and 45o S. The bulk of the records are from the South Pacific shores of Australia and New Zealand. There is one extralimital record from the Netherlands.

Head Shape

The melon may bulge slightly or not at all in front of the blowhole and slopes smoothly to the long and pointed beak. The mouthline is relatively straight.

Coloration

Adult males are darkly pigmented over entire body except for the rostrum and lower jaw which are white. Females are dark gray on the dorsal surface and light gray on the ventral surface, with patches of white around the umbilical scar, genital and anal slit and mammary slits. The lower jaw and upper lips are light gray. The flippers are darker than the surrounding body.

Size

Adult body length ranges between 5.3 to 5.8 m. Recorded maximum body length for adult males and females is 5.6 m and 5.8 m, respectively. Length at birth is 2.4 m.

Most Likely Confused With:

Mesoplodon layardii

Diagnostic features of the skull and mandible 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 transects the mesethmoid bone. Separates from Hyperoodon. Tooth alveoli of mandible are positioned b etween apex and posterior mandibular symphysis.Separates from Berardius, Ziphius, Tasmacetus,Indopacetus, Hyperoodon, M. bowdoini, M. carlhubbsi, M, ginkgodens, M. hectori, M. layardii, M. mirus, M. perrini, M. densirostris, M. peruvianus, M. stejnegeri, and M. traversii. Deep basirostral groove extends anteriorly well past the prominental turbercle. Separates from M. bidens and M. europaeus.

Diagnostic features of the skull and mandible 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 transects the mesethmoid bone. Separates from Hyperoodon. Tooth alveoli of mandible are positioned b etween apex and posterior mandibular symphysis.Separates from Berardius, Ziphius, Tasmacetus,Indopacetus, Hyperoodon, M. bowdoini, M. carlhubbsi, M, ginkgodens, M. hectori, M. layardii, M. mirus, M. perrini, M. densirostris, M. peruvianus, M. stejnegeri, and M. traversii. Deep basirostral groove extends anteriorly well past the prominental turbercle. Separates from M. bidens and M. europaeus.

Tooth position A single pair of large teeth are positioned back from the apex at 50 - 60% of total length of the mouthline. The tooth root is squared at its base and the teeth have a slight anterior incline or no incline at all. This is the only mesoplodont to have maxillary teeth. Up to 17-22 regularly spaced maxillary teeth begin at the same position along the jaw as the single pair of teeth in the lower jaw. There are no alveoli and they protrude only a few millimeters external to the gum. Tooth exposure Erupted teeth of adult males are covered in gum tissue with only the tips of the teeth exposed. Teeth in females and juveniles do not erupt. Tooth shape Anterior and posterior tooth margins are sinusoidal with the tooth apex slightly offset from the midline of the tooth.