Nenga meganasalis, 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 : 589-592

Nenga meganasalis n. sp.

HOLOTYPE. — SAM PQ 69675 , a partial skull including the rostrum, the premaxillary sac fossae, and the vertex.

REFERRED SPECIMENS. — SAM PQ 2117, a partial rostrum, trawled off the South African coast; SAM PQ 2339, a partial skull including the rostrum base, the premaxillary sac fossae, and the vertex, trawled off Cape coast; SAM PQ 69676, a partial rostrum and anterior of the cranium, trawled west of Cape Point, Atlantic Ocean (depth 347 m).

ETYMOLOGY. — From the Ancient Greek “megas”, large; “meganasalis” for the large nasals of this species.

TYPE LOCALITY. — No exact locality. Trawled west of Cape Town, Atlantic Ocean.

DIAGNOSIS. — Nenga meganasalis n. gen., n. sp. differs from all the other Ziphiidae in the nearly rectangular wide nasals occupying most of the vertex dorsally. It differs from the Ziphiinae in the mesorostral ossification of the mesethmoid and it lacks the main synapomorphy of the subfamily, the anterolaterally directed premaxillary crest. It differs from the Hyperoodontinae , Pterocetus n. gen., Tasmacetus , and Xhosacetus n. gen., in the mesorostral ossification of the mesethmoid and lacks the constriction of the ascending process of the premaxilla and the intrusion of the nasal in the narrow premaxillary crest. It differs from Ninoziphius in the rostrum elevated at its base and the reduction of the maxillary alveoli.

DESCRIPTION ( FIGS 21-23 ; TABLE 5)

The almost complete rostrum of the holotype is robust and long. The maxilla ends more than 45 mm from the apex. At mid-length, the rostrum is wider than high. The morphology of the rostrum base varies within the species: it is wider in SAM PQ 2339 and SAM PQ 69676 with a wide concave subhorizontal surface of the maxilla following anteriorly the large maxillary foramen. In the holotype and SAM PQ 2117, the dorsal surface of the maxilla narrows more rapidly anteriorly, while the lateral slope is more pronounced. The lateral margin of the maxilla at the rostrum base is acute. The vomer is weakly thickened or not at all in the widely open mesorostral groove. In specimen SAM PQ 69676, the mesorostral groove is posteriorly filled by the ossified mesethmoid for a length of more than 100 mm (specimen incomplete anteriorly); in this species the ossified mesethmoid might have occupied

A

choana

most of the length of the mesorostral groove. Shallow alveoli marks are still visible on the maxillary alveolar groove of the holotype.

The premaxillary sac fossa is large and slightly concave; it rises slowly posteriorly until the ascending process. The ascent to the vertex from this point is more abrupt, but barely reaching vertical. In anterior view, the lateral margins of the premaxillae are roughly parallel until the transversely directed, weakly laterally developed, premaxillary crests.

premaxillary premaxillary foramen

sac fossa

mesorostral groove

filled by the mesethmoid concave dorsal surface

The posterior projection of the premaxilla along the nasal contacts the frontal. The outline of the bony nares varies within the species being more V-shaped and longer in SAM PQ 2339.

In the holotype, several smaller foramina pierce the maxilla just behind the large maxillary foramen at the rostrum base. The relative position of maxillary and premaxillary foramina varies within the species, around the level of the antorbital notch.

The nasals occupy a large nearly rectangular surface on the wide and low vertex, much longer than the short strip of frontals (complete on SAM PQ2339), and wider than long. The lateral margin of the nasal is moderately convex and its anterolateral corner forms only a small part of the premaxillary crest. A vertical groove excavates the anterior margin of each nasal and the rounded anterior point of the nasals is only slightly more anterior than the premaxillary crests. The naso-frontal suture is roughly rectilinear. The morphology of the posterior portion of the vertex is not as well preserved as in Microberardius n. gen. and in the Berardiinae indet. described above. We therefore are unable to detect the presence or absence of the interparietal, preventing firm attribution to the subfamily Berardiinae (see phylogeny below).

Figures

FIG. 21. — Skull of Nenga meganasalis n. gen., n. sp. (SAM PQ 69675, holotype): A, dorsal view; B, lateral view; C, ventral view. Scale bar: 10 cm.

FIG. 22. — Nenga meganasalis n. gen., n. sp.: A-D, skull (SAM PQ 69675, holotype); A, detail of the vertex in dorsal view; B, corresponding line drawing; C, anterior view; D, corresponding line drawing; E, incomplete skull (SAM PQ 2339), dorsal view. Scale bars: A, B, 5 cm; C-E, 10 cm.

FIG. 23. — Rostrum of Nenga meganasalis n. gen., n. sp. (SAM PQ 69676), in dorsal view showing the mesorostral groove partially filled by the mesethmoid. Scale bar: 10 cm.