Ziphirostrum sp.

Bianucci, Giovanni, Miján, Ismael, Lambert, Olivier, Post, Klaas & Mateus, Octávio, 2013, Bizarre fossil beaked whales (Odontoceti, Ziphiidae) fished from the Atlantic Ocean floor off the Iberian Peninsula, Geodiversitas 35 (1), pp. 105-153 : 139-140

aff. Ziphirostrum sp.

( Fig. 19 ; Table 5)

REFERRED SPECIMEN. — SGHN MA0936, partial skull including rostrum and left part of facial area, A Selva fishing ground, depth of approximately 500 m, off the Galician coast, 44°10’N, 08°40’W.

DESCRIPTION ffle rostrum of this medium-size ziphiid is narrow and elongated, with size and proportions close to Ziphirostrum turniense (see Lambert 2005).

Premaxilla ffle premaxillae are distinctly swollen on the rostrum, contacting each other dorsomedially above the hollow mesorostral groove for most of the rostral length.ffle nearly fused medial suture is asymmetric, shifted to the right side on the posterior half of the rostrum. A similar asymmetry has been noted, but on the other side, on an isolated ziphiid rostrum from the Miocene of Maryland, USA ( Lambert et al. 2010). In lateral view, the maximum height and width of the premaxilla is more anterior than in Z. marginatum , more similar to Z. turniense . From mid-length of the rostrum, the premaxilla narrows considerably, and a medial separation appears 110 mm anterior to the level of the antorbital notch, with a progressive descent of the premaxilla in the prenarial basin, a feature absent in Choneziphius . ffle extent and depth of the basin is again more similar to Z. turniense , shallower than in Z. marginatum . Less anteriorly located than in the latter, the premaxillary foramen is on the floor of the basin, slightly anterior to the prominental notch.ffle partly preserved surface of the left premaxillary sac fossa is transversly convex, as in Ziphirostrum ,differing from the concave surface in Choneziphius and related taxa. ffle ascent towards the vertex is not abrupt.

Maxilla Even if the anterior part of the maxilla-premaxilla suture is difficult to detect, the anterior end of the maxilla is located 50-60 mm from the apex of the rostrum. Barely visible in dorsal view for the anterior half of the rostrum, the maxilla considerably widens towards the prominental notch, forming an elongated triangular surface. ffle posterior part of this surface, along the prenarial basin, displays a steep slope, with an elevated and thin lateral margin, more similar to Z. turniense . Considerably wider on the right side than on the left, the triangular surface is covered with numerous and high excrescences, a character found in Choneziphius , but also in Beneziphius and an isolated ziphiid rostrum from the Neogene of the North Sea (see Lambert 2005: fig. 26). ffle prominental notch and maxillary tubercle are conspicuous; this area is not well preserved in any specimen of Z. turniense . No marked maxillary crest extends posteriorly from the maxillary tubercle, differing from Choneziphius . ffle alveolar groove is vestigial, with shallow remains of alveoli still visible, a condition observed in several specimens of Z. marginatum and Z. turniense .

Palatine ffle palatine is preserved at the rostrum base, with a maxilla-palatine suture easy to distinguish. ffle rounded anterior end of the palatine is 130 mm anterior to the antorbital notch. An abrupt step in the surface of the palatine indicates the suture with the lost pterygoid.

REMARKS

Except for the development of excrescences on the dorsal surface of the maxilla on the posterior half of the rostrum and the distinct asymmetry of the premaxillae on the rostrum, this specimen is similar to the two specimens from the Neogene of the North Sea referred to Ziphirostrum turniense . ffle low diagnostic value of the excrescences on the maxilla has previously been demonstrated ( Lambert 2005) and the development of the premaxillae on the rostrum is known to vary within one species. ffle main features differentiating Z. turniense from the better-known Z. marginatum are observed here: maximum width and height of the premaxillae at

SGHN MA0936

Rostrum length 557

Distance from apex of rostrum to bony nares e635

Width of rostrum at mid-length 71

Width of premaxillae at mid-length of rostrum 49

Height of rostrum at mid-length 90

Width of rostrum base at prominental notch e120

Width of rostrum base at antorbital notch e208

Distance rostrum base – anterior apex of palatine 130

Preorbital width of skull e314

Longitudinal distance left premaxillary foramen-rostrum base 40

Width of left premaxillary sac fossa 49

mid-length of the rostrum, shallower prenarial basin, with dorsal exposure of the maxillae wider and more steeply sloping along the basin. ffle third species of the genus, Z. recurvus , is characterized by a more elevated rostrum with a complete filling of the mesorostral groove by the vomer, a feature lacking here. Because this specimen originates from a remote area, and because the vertex is lacking, as in specimens of Z. turniense and Z. recurvus , we prefer to maintain the attribution Ziphiidae aff. Ziphirostrum sp. , pending the discovery of more complete specimens.

Figures

FIG. 19. — Skull of aff. Ziphirostrum sp. (SGHN MA0936):A, dorsal view; B, ventral view; C, lateral view.Parallel lines indicate a break surface. Scale bar: 10 cm.