Izikoziphius rossi, 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 : 570-573

Izikoziphius rossi n. sp.

HOLOTYPE. — PEM N 3265 , a partial skull including the rostrum, the anterior part of the cranium, and the vertex.

REFERRED SPECIMEN. — SAM PQ 2086, a partial skull including the rostrum, the anterior part of the cranium, and the vertex, trawled off the South African coast

ETYMOLOGY. — Honouring Dr. Graham J. B. Ross, a cetologist formerly at the PEM who studied in detail extant cetaceans, including the ziphiids, of South African waters.

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

DIAGNOSIS. — Izikoziphius rossi n. gen., n. sp. differs from I. angustus n. gen., n. sp. in: rostrum wider than high at mid-length; wide rostrum base; maxillary crest extending on the rostrum base; wide fossa on the anterior surface of the ascending process of the right premaxilla excavating the nasal; anteromedian depression of the dorsal surface of the nasals and a distinctly more elevated right side of the vertex.

DESCRIPTION ( FIGS 6-9 ; TABLE 2)

The rostrum is wider than high at mid-length. The rostrum base is particularly wide (more prominent in the holotype); the lateral margin of the subhorizontal platform of the maxilla present from midway along the rostrum progressively diverges and rises to a crest towards the antorbital notch. The highest dome-like portion of the crest is located on the preorbital process. Medially to this dome, the large maxillary foramen opens anterolaterally with a circular section.

The premaxilla is longer anteriorly than the maxilla. The alveolar groove is either absent or much reduced.

The mesorostral groove is filled with the thickened vomer, but a wide median groove is retained posteriorly.The maximum elevation of the vomer is around two thirds of the length of the rostrum in SAM PQ 2086, less pronounced in PEM N 3265.

The narrow premaxillary foramen, posterior to the antorbital notch, is depressed compared to the slightly concave premaxillary sac fossa. The elevated lateral margin of the fossa overhangs the maxilla along its posterior half. The lateral margins of the ascending processes of the premaxillae are parallel until the elevated vertex. The vertical anterior surface of each ascending process is hollowed out by a deep elliptical fossa, extending medially on the anterolateral surface of the nasal. The right fossa is wider than the left. In relation to the morphology of the air sacs connected to the nasal passages and the surrounding bony configuration in Recent ziphiids and other odontocetes ( Heyning 1989; Cranford et al. 1996), this fossa corresponds to the location of the posterior nasal sac (sensu Heyning 1989, more generally the caudal sac in Cranford et al. 1996). We suggest that in Izikoziphius n. gen. a homologous air sac was located in this elliptical fossa. A pair of smaller fossae is present ventromedially at the naso-mesethmoid suture (best seen in SAM PQ 2086), probably related to the foramina of the terminal nerve. The mesethmoid is weakly or not keeled under the nasals.

The relatively thin premaxillary crests are anterolaterally directed. The right crest is twice longer than the left (best preserved in PEM N 3265).

The large nasals, widest at mid-length and slightly longer than wide, are anteriorly longer than the premaxillary crests. Their dorsal surface is slightly anteromedially depressed. The naso-frontal suture is posteriorly irregularly convex with the right nasal longer than the left. The frontals were originally probably short.

In anterior view, the right side of the vertex is considerably higher than the left side.

infraorbital foramen

Figures

FIG. 6. — Skull of Izikoziphius rossi n. gen., n. sp. (PEM N 3265, holotype): A, dorsal view; B, lateral view; C, ventral view. Scale bar: 10 cm.

FIG. 7. — Vertex of skull of Izikoziphius rossi n. gen., n. sp. (PEM N 3265, holotype): A, dorsal view; B, corresponding line drawing; C, anterior view; D, corresponding line drawing. Scale bars: A, B, 5 cm; C, D, 10 cm.

FIG. 8. — Skull of Izikoziphius rossi n. gen., n. sp. (SAM PQ 2086): A, dorsal view; B, anterior view; C, lateral view; D, ventral view. Scale bar: 10 cm.

FIG. 9. — Vertex of skull of Izikoziphius rossi n. gen., n. sp. (SAM PQ 2086): A, dorsal view; B, corresponding line drawing; C, anterior view; D, corresponding line drawing. Scale bars: 5 cm.