Pterocetus aff. 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 : 597-598

Pterocetus aff. benguelae

REFERRED SPECIMENS. — SAM PQ 1770, partial skull including the rostrum and most of the dorsal surface of the cranium with vertex, trawled 6.4 km west of Slang-

kop, Atlantic Ocean, depth of 274 m; SAM PQ 2751, rostrum, trawled off the South African coast.

DESCRIPTION AND DISCUSSION

(FIGS 28; 29C, D; TABLE 5)

The general shape and the anterior position of the premaxillary foramen cause us to refer the two specimens to Pterocetus n. gen. Moreover, SAM PQ 1770 shows the deep and wide antorbital notch characteristic for Pterocetus n. gen. Nevertheless, both specimens differ from those referred above to Pterocetus benguelae n. gen., n. sp. in their lower rostrum with an anteriorly flatter ventral surface. This difference in robustness might correspond to an intraspecific sexual dimorphism, as observed in the extant Mesoplodon densirostris , whose rostrum is considerably more robust in the males than in the females ( Fig. 30 ).

mesethmoid bony nares

FIG. 28. — Skull of Pterocetus aff. benguelae (SAM PQ 1770) : A, dorsal view; B, anterior view; C, lateral view; D, detail of the vertex in dorsal view; E, corresponding line drawing. Scale bars: A-C, 10 cm; D, E, 5 cm.

However, in this case the difference in robustness of the rostrum is reinforced by the strong mesorostral ossification of the vomer, mostly present in the adult male, while both the robust and slender fossil rostra described above exhibit a complete mesorostral ossification. Other small differences are observed between SAM PQ 1770 and the holotype of Pterocetus benguelae n. gen., n. sp. at the level of the vertex: the nasals are narrower, the bony nares are smaller, the premaxillary crest seems laterally less developed, and the constriction of the ascending process is almost absent. Considering these differences, referral of SAM PQ 1770 and SAM PQ 2751 to Pterocetus aff. benguelae seems justified.

Figures

FIG. 30. — A, B, rostrum of male of Mesoplodon densirostris (SAM ZM 40663); A, dorsal view; B, lateral view; C, D, rostrum of female of M. densirostris (SAM ZM 40836); C, dorsal view; D, lateral view. Reduced to the same lenght.