Xhosacetus hendeysi, 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 : 592-595

Xhosacetus hendeysi n. sp.

HOLOTYPE. — SAM PQ 2082 , a partial skull including most of the rostrum, anterior part of the cranium, and the vertex.

ETYMOLOGY. — Honouring Dr. Q. Brett Hendey, geologist and palaeontologist formerly at the SAM who dedicated his career to Tertiary terrestrial and marine mammals from South Africa, particularly from the famous site of Langebaanweg.

TYPE LOCALITY. — No data. Trawled off the South African coast.

DIAGNOSIS. — Xhosacetus hendeysi n. gen., n. sp. differs from all other ziphiids except Nenga n. gen. in possessing relatively large nasals, as wide as long, with roughly parallel lateral margins. It further differs from members of the Berardiinae and Ziphiinae in: the short intrusion of the nasal in the premaxillary crest; the filling of the mesorostral groove by the vomer at least partly by thickening of the lateral walls and from the Berardiinae in a moderate constriction of the ascending process of the premaxilla. It differs from the Hyperoodontinae and Ziphiinae in the transversely oriented premaxillary crest. It further differs from the Hyperoodontinae , Pterocetus n. gen., and Tasmacetus in the lack of an anteromedian depression of the nasals and from the same group, except Khoikhoicetus n. gen., in a weaker constriction of the ascending process of the premaxilla. It differs from Tasmacetus in: smaller size, mesorostral groove filled with ossified vomer and shallower alveolar groove. It differs from Ninoziphius in: elevated and narrow rostrum, mesorostral groove filled with ossified vomer and reduction of the maxillary alveoli.

DESCRIPTION ( FIGS 24 ; 25 ; TABLE 5)

The anterior part of the rostrum is not complete; it might have originally measured 500 mm; its preserved part is higher than wide. The surface of the premaxilla is nearly vertical anteriorly. The widening of the rostrum posteriorly is progressive up to the faint prominental notch, followed by an abrupt divergence towards the antorbital notch. The shallow alveolar groove has slightly depressed areas interpreted as remains of alveoli.

The vomer completely fills the mesorostral groove and its height in the groove decreases anteriorly. A deep sulcus separates the thickened vomer from the premaxilla laterally for its whole length. At the rostrum base, a median suture between the two walls of the vomer joins the anterior point of the ossified mesethmoid, at the level of the prominental notch.

The premaxillary foramen is located just posterior to the shallow antorbital notch. The concave premaxillary sac fossae are weakly asymmetric. In anterior view a distinct constriction marks the lateral margin of the ascending process of the premaxilla.

A sharp maxillary crest separates the large maxillary foramen from the antorbital notch. The lateral slope of the crest, leading to the laterally developed preorbital process, is weaker than the median slope. The left crest is more robust. The lacrimal bears a prominent knob-like anterolateral projection.

The vertex is moderately elevated and the dorsal part of the ascending process of the premaxilla is vertical. The premaxillary crest is moderately thickened and transversely oriented, slightly overhanging the premaxillary sac fossa on the right side. The posterior projection of the premaxilla along the nasal contacts the frontal on both sides. The nasals are large, as wide as long, with roughly parallel lateral margins. The right nasal is somewhat wider and longer than the left nasal. The dorsal surface of the nasals is slightly sloping without an anteromedian depression; the anterior margin is excavated by a vertical groove and the anterolateral corner forms only a small part of the premaxillary crest. The frontal was originally probably much shorter than the nasal.

Figures

FIG. 24. — Skull of Xhosacetus hendeysi n. gen., n. sp. (SAM PQ 2082, holotype):A, dorsal view; B, lateral view; C, ventral view. Scale bar: 10 cm.

FIG. 25. — Skull of Xhosacetus hendeysi n. gen., n. sp. (SAM PQ 2082,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.