Mesoplodon slangkopi, Bianucci & Lambert & Post, 2007

Bianucci, Giovanni, Lambert, Olivier & Post, Klaas, 2007, A high diversity in fossil beaked whales (Mammalia, Odontoceti, Ziphiidae) recovered by trawling from the sea floor off South Africa, Geodiversitas 29 (4), pp. 561-618 : 586-589

Mesoplodon slangkopi n. sp.

HOLOTYPE. — SAM PQ 2069 , partial skull including the rostrum base and the dorsal surface of the cranium with the vertex.

REFERRED SPECIMEN. — SAM ZM 35107, partial skull including the deeply worn rostrum base, the premaxillary sac fossae, and the vertex, trawled off the South African coast.

ETYMOLOGY. — The holotype was found offshore from Slangkop (meaning snake head in old Dutch), a locality on the south coast of South Africa.

TYPE LOCALITY. — No exact locality. Trawled off Slangkop, Cape Province.

DIAGNOSIS. — Mesoplodon slangkopi n. sp. is a small member of the genus, with cranial dimensions close to M. perrini and M. peruvianus . It shares with M. carlhubbsi , M. densirostris , M. grayi , and M. layardii the extension of the ventral margin of the alveolar groove until the prominental notch. The rostrum base is narrower than in M. bidens , M. bowdoini , M. europaeus , M. ginkgodens , M. hectori , M. mirus , M. peruvianus , M. stejnegeri , and M. traversii ; the prominental notch is more excavated than in M. bidens , M. hectori , M. mirus , M. perrini , M. peruvianus , and M. stejnegeri ; the maxillary crest is distinctly lower than in M. bowdoini , M. carlhubbsi , M. europaeus , M. ginkgodens , M. mirus , and M. traversii ; the maxillary ridge along the lateral margin of the supraorbital process is much lower than in M. carlhubbsi and M. layardii ; the premaxillary foramen is more anterior, closer to the level of the antorbital notch, than in M. bowdoini , M. carlhubbsi , M. densirostris , and M. stejnegeri ; the premaxillary sac fossae and premaxillary crests are less asymmetric than in M. layardii and M. traversii ; the distance between the premaxillary crests is shorter than in M. carlhubbsi , M. layardii , and M. mirus ; the premaxillary crest (especially the right crest) is laterally shorter than in M. bowdoini , M. carlhubbsi , M. densirostris , M. layardii , M. mirus , and M. traversii ; the premaxillary crest overhangs the bony nares more than in M. grayi , less than in M. bowdoini and M. traversii , the nasal is shorter along the median margin of the premaxillary crest than in M. bowdoini , M. ginkgodens , and M. traversii ; the nasal is longer posteriorly, compared to the frontal, than in M. bidens , M.xcarlhubbsi , M. densirostris , M. hectori , M. layardii , M. peruvianus , and M. stejnegeri and the vertex is wider posterior to the premaxillary crests than in M. grayi , M. peruvianus , and M. traversii .

DESCRIPTION ( FIGS 19 ; 20 ; TABLE 4)

From its base, the rostrum quickly narrows forwards. The anterior part is unknown but the rostrum is

much higher than wide along its preserved part; it is particularly narrow compared to the width of the cranium at the antorbital notch, a condition somewhat similar to Mesoplodon grayi . The vomer fills the mesorostral groove, forming a hump at the rostrum base; a median suture is seen on its dorsal surface, shifted to the left. The alveolar groove is distinct until the rostrum base; the ventral margin of the groove extends to the prominental notch and is visible in dorsal view, strengthening the lateral margin of the rostrum base, as in M. grayi , and M. layardii . Shallow depressions in the groove indicate remnants of alveoli. The maxilla-palatine suture is pointed and located 87 mm anterior to the antorbital notch. The preserved anterior part of the pterygoid is robust and anterolaterally limits an elliptical pterygoid sinus fossa distinctly anterior to the prominental notch.

A small foramen pierces the maxilla close to the wide prominental notch. Only a low crest follows the prominent maxillary tubercle posteriorly. A low maxillary ridge extends parallel to and near the lateral margin of the supraorbital process.

The premaxillary foramen is located at the level of the antorbital notch. The ascending process of the premaxilla is strongly constricted in anterior view; the lateral margins of the bony nares are strongly converging dorsally.

The vertex is moderately elevated and transversely compressed in its posterior part. The thick and wide, distinctly posterolaterally directed and asymmetric premaxillary crests overhang the ascending process and the bony nares. The distance between the two crests is small and an oblique transverse groove limits ventrally the anterior surface of each crest, with a general configuration close to M. densirostris . The posterior projection of the premaxilla along the nasal is approximately as long as the nasal and much widened, especially on the right side, similar to M. hectori . The lateral margins of the elongated nasals are parallel; the anterolateral corner of each nasal is included in the corresponding premaxillary crest for approximately half the median length of the crest. The anteromedian excavation of the nasals is deep and narrow. The frontals were probably much shorter than the nasals.

Figures

FIG. 19. — Skull of Mesoplodon slangkopi n. sp. (SAM PQ 2069, holotype): A, dorsal view; B, lateral view. Scale bar: 10 cm.

FIG. 20. — Skull of Mesoplodon slangkopi n. sp. (SAM PQ 2069, holotype): A, ventral view; B, detail of the vertex in dorsal view; C, corresponding line drawing; D, anterior view; E, corresponding line drawing. Scale bars: A, D, E, 10 cm; B, C, 2 cm.