Odontoceti, Flower, 1867

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 : 599-601

Odontoceti indet.

REFERRED SPECIMENS. — SAM PQ 2717, isolated rostrum, trawled off Saldanha Bay, west coast of South Africa, Atlantic Ocean, depth of 366 m; SAM PQ 2719, isolated rostrum, trawled off the South African coast.

DESCRIPTION AND DISCUSSION ( FIGS 31 ; 32 )

The isolated rostra SAM PQ 2717 and SAM PQ 2719, preserved for a length of respectively 519

A premaxilla maxilla thickened vomer

and 547 mm, are characterized by a very unusual structure.

The premaxilla is weakly modified compared to the general odontocete plan. It occupies the margins of the mesorostral groove in dorsal view and the upturned apex of the rostrum, ventrally appearing on the first third of the rostrum. At the apex of the maxilla, the rostrum has a width of respectively 60 and 45 mm for SAM PQ 2717 and SAM PQ 2719 and a height of respectively 56 and 44 mm. The mesorostral groove is partially filled by the thickened lateral walls of the vomer, leaving an open median V-shaped groove. The development of the vomer in the mesorostral groove combined with high-density bone tissue is mostly observed in ziphiids (see above). Ventrally, the exposure of the vomer is respectively 290 and 240 mm.

The maxilla is highly modified; the lateral margin is considerably elevated laterodorsally along the posterior two thirds of the rostrum. This lateral maxillary crest is robust at its base, progressively thinning dorsally. The maximum height of the crest is mid-way along the rostrum.The two crests anteriorly delimit a wide and deep basin, ending at some distance before the apex of the maxilla. The inner wall of the crest is striated with vascularization sulci, best seen in SAM PQ 2717. On this specimen, the outer wall of the crest, continuous with the wide ventral surface of the rostrum, bears a shallow alveolar groove punctuated by a series of rounded protuberances interpreted as unerupted teeth. No alveolar groove is observed in SAM PQ 2719. The basin is considerably larger in SAM PQ 2717 (maximum width and height of the rostrum respectively 230 and 201 mm), a difference that might correspond to sexual dimorphism, as seen in Physeter macrocephalus for the supracranial basin, in Ziphius cavirostris for the prenarial basin, and in Hyperoodon spp. for the maxillary crests.

Similarities with Hyperoodon spp. at the level of the maxillary crests are functionally rejected: the high maxillary crests of the latter do not form a basin. If the prenarial basin of Z. cavirostris is differently built, the supracranial basin of the physeterids bearing the spermaceti organ is relatively similar, especially in P. macrocephalus . Significant thickening of the vomer has not been described in physeterids until now and we therefore may not refer with certainty these relatively small specimens to the Physeteridae . On the other hand, their maxilla differs significantly from the known ziphiids. Future information about the bony nares and additional cranial characters would be crucial to solve the familial affinities of this strange whale.

Figures

FIG. 31. — Rostrum of Odontoceti indet. (SAM PQ 2717): A, dorsal view; B, lateral view; C, ventral view. Scale bar: 10 cm.

FIG. 32. — A-C, rostrum of Odontoceti indet. (SAM PQ 2717); A, detail of the alveolar groove; B, anterior view; C, anterolateral view; D-G, rostrum of Odontoceti indet. (SAM PQ 2719); D, dorsal view; E, lateral view; F, anterior view; G, anterolateral view. Scale bars: 10 cm.