Africanacetus ceratopsis, 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 : 583-586

Africanacetus ceratopsis n. sp.

HOLOTYPE. — NMR 9991-00001993, a partial skull including the rostrum and the dorsal part of the cranium with the vertex.

REFERRED SPECIMENS. — SAM PQ 2162 , trawled off Cape coast ; SAM PQ 2235 , trawled off Cape coast, Atlantic Ocean ; SAM PQ 2708 , trawled at 35°01’S, 24°06’E, south coast of South Africa, Indian Ocean , depth of 914 m ; SAM PQ 2709 , trawled at 35°01’S, 24°06’E, south coast of South Africa, Indian Ocean , depth of 914 m ; SAM PQ 2713 , trawled at 35°01’S, 24°06’E, south coast of South Africa, Indian Ocean , depth of 914 m ; SAM PQ 3002 , trawled at 34°50’S 18°14’E, south of Cape Town , depth of 604 m ; SAM PQ 3062 , trawled off Cape coast ; SAM PQ 69683 , trawled off Cape Peninsula , between Cape Point and Slangkop lighthouse, depth of 160- 170 m. Most of the referred specimens are rostra, usually preserved with the anterior of the cranium, but lacking the vertex. SAM PQ 69683 is an isolated vertex .

ETYMOLOGY. — From the combination of the following two Ancient Greek words: “keras” (genitive “keratos”), horn, and “opsis”, aspect, appearance. For the protuberant paired maxillary crests.

TYPE LOCALITY. — No exact locality. Trawled south west off the South African coast, Atlantic Ocean, depth less than 600 m.

DIAGNOSIS. — Africanacetus ceratopsis n. gen., n. sp. differs from all other Hyperoodontinae in: presence of a dome-like elevated maxillary crest on the supraorbital process and laterally sloping premaxillary sac fossa. It shares with Ihlengesi n. gen., Hyperoodon , and Mesoplodon : the dorsal part of the ascending process of the premaxilla partly overhanging the bony nares, and the larger portion of the nasal thrust into the premaxillary crest, differing in these characters from Khoikhoicetus n. gen. and Indopacetus . It further differs from Hyperoodon and Mesoplodon in the wide median separation of the premaxillary crests.

DESCRIPTION ( FIGS 17 ; 18 ; TABLE 4)

The robust rostrum is long (rostrum of SAM PQ 2235 originally longer than 671 mm) and elevated, higher than wide over its entire length. The vomer fills the mesorostral groove, showing a median suture, between its two thickened lateral walls, on its posterior part; the vomer is more elevated than the premaxilla over its complete length. The width of the vomer in the groove varies within the species, sometimes occupying most of the dorsal surface of the rostrum (e.g., SAM PQ 3002). It widens at mid-length on several specimens. At the contact with the premaxilla, the vomer usually shows a slight constriction and therefore the dorsal prominent part of the vomer slightly overhangs the premaxilla. The alveolar groove is barely visible.

The lateral margins of the rostrum diverge abruptly towards the prominental notches, creating a wide concave dorsal surface of the maxilla at the rostrum base, with an acute lateral margin. The antorbital

A dome-like maxillary crest

premaxillary premaxilla premaxillary crest crest

notch, separated from the prominental notch by a distinct maxillary tubercle, is positioned roughly at the longitudinal level of the premaxillary foramen. Posteromedial to the maxillary tubercle rises a characteristic elevated dome-like maxillary crest, not extending onto the rostrum base. The median slope of the dome is nearly vertical. In several specimens a large maxillary foramen is transversely compressed between this crest and the premaxilla, somewhat more posterior than the premaxillary foramen.

The premaxillary sac fossa is thicker medially, laterally lowering as in Mesoplodon layardii . The ascending process is short and constricted in anterior view; the upper part of its anterior surface is vertical. The lateral margins of the bony nares continue parallel dorsally. On the moderately elevated vertex, the premaxillary crest is thick, wide, and posterolaterally directed. The robust posterior projection of the premaxilla along the nasal contacts the frontal.

The nasals are distinctly wider anteriorly, with the anterolateral corner included in the posterior half of the premaxillary crest. The anteromedian surface of the nasals is excavated, leaving a large space between the premaxillary crests. The nasofrontal suture is W-shaped; the right nasal is longer than the left. The frontal is much shorter than the nasal on the vertex.

Figures

FIG. 17 – Skull of Africanacetus ceratopsis n. gen., n. sp. (NMR 9991-00001993, holotype); A, dorsal view; B, lateral view; C, anterior view; D, corresponding line drawing. Scale bar: 10 cm.

FIG. 18. — Africanacetus ceratopsis n. gen., n. sp.: A-C, skull (NMR 9991-00001993, holotype); A, ventral view; B, detail of vertex in dorsal view; C, corresponding line drawing. D, E, skull fragment (vertex) of Africanacetus ceratopsis n. gen., n. sp. (SAM PQ 69683); D, dorsal view; E, corresponding line drawing. Scale bars: A, 10 cm; B-E, 5 cm.