Pterocetus benguelae, 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 : 595-597

Pterocetus benguelae n. sp.

HOLOTYPE. — SAM PQ 2803 , partial skull including most of the rostrum, the anterior part of the cranium, and the vertex.

REFERRED SPECIMENS. — SAM PQ 69684, partial skull including a part of the rostrum and anterior part of the cranium, trawled west of Cape Town, Atlantic Ocean; SAM PQ 2163, partial skull including rostrum base and anterior part of the cranium, trawled off the South African coast.

ETYMOLOGY. — From Benguela Current, the oceanic current running along south-east Africa, probably since the Miocene epoch. The holotype of this species was found off the west coast of South Africa.

TYPE LOCALITY. — No exact locality. Trawled south of Saldanha Bay, west coast of South Africa, Atlantic Ocean, depth of 700 m.

DIAGNOSIS. — Pterocetus benguelae n. gen., n. sp. differs from all other Ziphiidae in wider and deeper antorbital notch with much anterolaterally developed preorbital process and from all other Ziphiidae , except Indopacetus and Ziphirostrum , in the premaxillary foramen positioned distinctly anterior to the level of the antorbital notch. It shares with the Hyperoodontinae , and Tasmacetus an anteromedian depression of the dorsal surface of the nasals and a strong constriction of the ascending process of the premaxilla. It differs from Hyperoodontinae in lesser dorsomedial reabsorbing of the nasals. It differs from Tasmacetus in: smaller size; less pointed rostrum with narrower rostrum base; mesorostral groove filled with vomer and a shallower alveolar groove. It further differs from Xhosacetus n. gen. in the lower maxillary crest. It differs from Ninoziphius in: elevated and narrow rostrum; mesorostral groove filled with ossified vomer and reduction of the maxillary alveoli.

DESCRIPTION ( FIGS 26 ; 27 ; 29A, B; TABLE 5) None of the three known specimens includes the apex of the rostrum; several centimetres are probably missing in the holotype and SAM PQ 69684 .

The rostrum is moderately elongated, slightly higher than wide with lateral margins parallel for most of its length. The mesorostral groove is completely filled by the vomer. A distinct median suture is visible on the vomer for the first centimetres of the rostrum base, indicating a posterior development of the bone by thickening of the lateral walls until their median contact. A shallow alveolar groove is still present without alveoli marks. The acute ventral margin of the alveolar groove extends until the antorbital notch where it ventrally limits a small basin.

The premaxillary foramen is located distinctly anterior to the antorbital notch, which indicates an elongated premaxillary sac fossa, a character also present in Indopacetus . An even more anterior position of the premaxillary foramen is seen for example in Ziphius cavirostris and Ziphirostrum marginatum , but associated with a deep prenarial basin. A large circular maxillary foramen opens anterodorsally just medial to the antorbital notch. The notch is widely open and deep, because of the strong development of the preorbital process, which forms a peculiar anterolateral extension of the cranium. In anterior view, the frontal is visible in the preorbital process between maxilla and lacrimal.

In anterior view, the ascending process of the premaxilla is strongly constricted ventral to the vertical, thick and wide, transversely directed premaxillary crest.

On the moderately elevated vertex, the nasals are wide and pentagon-shaped. Their anterolateral corner extends only a short distance into the premaxillary crest. A vertical groove excavates the anterior margin of each nasal. The right nasal is longer posteriorly than the left. The dorsal surface of the nasals is slightly depressed anteromedially, similar to Tasmacetus . Posteriorly, the frontals are narrower than the nasals with a minimum length of 21 mm. On the vertex, the frontal is contacted by the long posterior projection of the premaxilla.

Figures

FIG. 26. — Skull of Pterocetus benguelae n. gen., n. sp. (SAM PQ 2803, holotype): A, dorsal view; B, ventral view; C, lateral view. Scale bar: 10 cm.

FIG. 27. — Skull of Pterocetus benguelae n. gen., n. sp. (SAM PQ 2803, holotype): A, detail of the vertex in dorsal view; B, corresponding line drawing; C, anterior view; D, corresponding line drawing. Scale bars: A, B, 5 cm; C, D, 10 cm.

FIG. 29. — A, B, incomplete skull of Pterocetus benguelae n. gen., n. sp.(SAM PQ 69684);A, dorsal view; B, lateral view; C, D, rostrum of P. aff. benguelae (SAM PQ 2751); C, dorsal view; D, lateral view. Scale bar: 10 cm.