Nenga sp.

Lambert, Olivier, Muizon, Christian de, Duhamel, Guy & Plicht, Johannes Van Der, 2018, Neogene and Quaternary fossil remains of beaked whales (Cetacea, Odontoceti, Ziphiidae) from deep-sea deposits off Crozet and Kerguelen islands, Southern Ocean, Geodiversitas 40 (6), pp. 135-160 : 155-156

Nenga sp. aff. Nenga meganasalis

Bianucci, Lambert & Post, 2007

REFERRED SPECIMEN AND LOCALITY. — Partial cranium MNHN.F.COI11 including rostrum, premaxillary sac fossae, and vertex ( Fig. 13 ); geographic coordinates 49°40’42.0”S, 63°44’18.0”E ( Skiff Bank , 365 km SWW to Kerguelen Islands) ; depth 1263 m ( Fig. 1 ).

BRIEF DESCRIPTION AND COMPARISON

Although missing the antorbital regions, this skull is characterized by an elongated rostrum, with a cross section at mid-length roughly as wide as high. On the anterior half of the rostrum the wavy floor of the alveolar groove suggests the presence of shallow, vestigial alveoli. Along its posterior half, the lateral margin of the rostrum diverges posterolaterally, as a relatively thin crest whose posterolateralmost portion is missing. The mesorostral groove is only partly filled with the vomer; the posteriormost part of the groove is empty, with the transversely concave floor rising anterodorsally. A large dorsal infraorbital foramen is partly preserved on the maxilla, at the same anteroposterior level as the premaxillary foramen. This foramen is followed anteriorly by a transversely concave area. The premaxillary foramen is relatively distant from the bony nares and close medially to the mesorostral groove. The premaxillary sac fossae are proportionally long, with a progressive posterodorsal rise. The right premaxillary sac fossa is much wider than the left, with a markedly rounded lateral margin in dorsal view. The dorsal surface is slightly transversely concave and the anteromedial angle is well defined. The narrow left fossa is similarly slightly transversely concave, with a less marked anteromedial angle. Taking into account that the lateralmost surface of the premaxillary crests is probably somewhat abraded, the lateral margin of each ascending process of the premaxilla is barely constricted in anterior view. The anterior surface of each premaxillary crest is not vertical. The left premaxillary crest is directed laterally, whereas the right is directed laterally and slightly posterolaterally. The nasals occupy a large part of the dorsal surface of the vertex, with a maximum width roughly at mid-length; they do not contribute to the corresponding premaxillary crest. The dorsal surface forms a shallow medial depression, without any marked anteroventral slope. The anteromedial tip of the joined nasals is slightly anterior to the premaxillary crests. The frontals are preserved on the vertex as a relatively short stripe of bone.

The large size of the nasals on the vertex, the transversely directed premaxillary crest, the lateral margin of the proportionally long ascending process of the premaxilla barely constricted in anterior view, and the long and highly asymmetric premaxillary sac fossae are features shared with Nenga meganasalis . In addition, the absence of filling of the posterior part of the mesorostral groove in MNHN.F.COI11 may indicate some degree of development of the presphenoid in this region, as seen in one specimen of N. meganasalis (SAM PQ 69676). Most of the measurements of COI11 correspond well with the cranial dimensions of N. meganasalis , except for the distinctly longer rostrum (as compared to the holotype of N. meganasalis , possibly lacking only a short part of the apex; Table 10) and the narrower nasals in the former. These differences and the fragmentary state of COI11 (see for example the poorly preserved dorsal surface of the rostrum) prevent from a firm attribution to the species N. meganasalis .

RADIOMETRIC DATING (14C)

FOR MESOPLODON SP. AFF. M. LAYARDII

The results of the analysis of the two samples are shown in Table 11. The values obtained indicate that the quality parameters of the collagen are excellent in both samples. The stable isotope ratios are consistent with the marine environment.

The calibrated results (including correction for the reservoir effect) are shown in Table 12, with all dates (BP, calBP and uncertainties) rounded to the nearest 5. The specimen MNHN.F.COI5 yields an age of 10 270-10 200 calBP (earliest Holocene) and the specimen COI6 an age of 12 670-12 575 calBP (latest Pleistocene). The calibrated date ranges are given at 1-sigma confidence level.

Figures

FIG. 13. — Partial cranium of Nenga sp. aff. Nenga meganasalis (MNHN.F.COI11): A, dorsal view; B, same view with interpretive line drawing; C, anterodorsal view; D, detail of the vertex in dorsal view; E, right lateral view. Scale bar: 100 mm.

FIG. 1. — Locality maps: A, schematic map providing the position of Crozet and Kerguelen islands in the Southern Ocean; B, schematic map of the Crozet and Kerguelen islands area, including the main localities where fossil ziphiid specimens («) described in this work were found via longline fishing,as well as two ODP sites (l). Light grey shading for areas with a water depth lower than 1000 m; dark grey shading for islands and continents.