Choneziphius leidyi, Bianucci & Miján & Lambert & Post & Mateus, 2013

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 : 111-115

Choneziphius leidyi n. sp.

(Figs 2-5; Table 1)

HOLOTYPE. — SGHN MA0633, partial skull including rostrum, facial area and vertex.

REFERRED SPECIMENS. — SGHN MA0640, partial skull including rostrum, facial area and vertex, Escarapote fishing ground, depth of approximately 685 m, off the Galician coast, 42°08’N, 09°26’W ; SGHN MA0641, partial skull including posterior portion of rostrum, part of facial area and vertex, A Selva fishing ground, depth of approximately 500 m, off the Galician coast, 44°10’N, 08°40’W ; SGHN MA0937, partial skull including rostrum and facial area, A Selva fishing ground, depth of approximately 500 m, off the Galician coast, 44°10’N, 08°40’W ; ML 533, partial skull including rostrum and facial area, south of Nazaré Canyon , off the Portuguese coast, exact locality unknown but likely around 39°18’N, 9°47’W ; ML 1366, fragment of skull including the left dorsal surface of the cranium with the left premaxillary crest, south of Nazaré Canyon off the Portuguese coast, exact locality unknown, but likely around 39°18’N, 9°47’W .

ETYMOLOGY. — In honour of the American palaeontologist Joseph Leidy (1823-1891), who described several Choneziphius -like fossil ziphiids from the Mid Atlantic Coastal Plain of the USA in 1876 and 1877.

TYPE LOCALITY. — A Selva fishing ground, depth of approximately 500 m, off the Galician coast, 44°10’N, 08°40’W.

DIAGNOSIS. — Large species of Choneziphius differing from C. planirostris in: longer and more pointed rostrum with apex constructed of premaxillae alone; longer dorsal opening of the mesorostral groove at the apex of the rostrum; premaxillary foramina located distinctly anterior to level of prominental notch; lower maxillary crest on the supraorbital process; shallower and wider premaxillary sac fossae; less asymmetric premaxillary sac fossae; higher vertex overhanging the bony nares.

DESCRIPTION ffle rostrum, although longer than in Choneziphius planirostris , exhibits the same massive appearance; in both species it is relatively narrow with a subcylindrical anterior half portion. As in C. planirostris , the facial area is wider than long. Differing from C. planirostris , the bony nares are not visible in dorsal view, being hidden by the overhanging and anteriorly projected vertex.

Premaxilla

On the complete rostra of the holotype and SGHN MA0640, the apex of the rostrum is formed by the premaxillae only, contrary to C. planirostris where maxilla and premaxilla both reach the apex of the rostrum. Anteriorly, the premaxillae are not fused dorsally, leaving the narrow tunnel-shaped mesorostral groove open for a length of at least 80 mm. Such a dorsal exposure of the mesorostral groove is rarely present in the large sample of C. planirostris , and, if present, never longer than 50 mm. For most of the rostrum length, the thick premaxillae are firmly fused at midline, with a suture remaining visible until the bony nares (as in C. planirostris ).

As in C. planirostris , the fused premaxillae form a prominent ridge at the rostrum base, posteriorly shifted to the left and separating the deeply excavated anterior portions of the premaxillary sac fossae (the main character defining the genus Choneziphius ). Each premaxillary sac fossa contains a premaxillary dorsal infraorbital foramen

FIG. 2. — Skull of Choneziphius leidyi n. sp. (SGHN MA0633, holotype): A, dorsal view; B, corresponding line drawing. Tight parallel lines indicate a break surface; more widely spaced parallel lines indicate superficial wear. Scale bar: 10 cm.

foramen at its anteriormost point, located well anterior to the level of the prominental notch of the maxilla (Fig. 2). In C. planirostris , the premaxillary foramen is located at, or just posterior to, the level of the prominental notch. An additional foramen is observed on the medial margin of the left premaxillary sac fossa of SGHN MA0640. ffle right premaxillary sac fossa is distinctly wider than the left (ratio between maximum width of left and right fossae between 0.70 and 0.76, n = 3), and

A

B

jugal

FIG. 3. — Skull of Choneziphius leidyi n. sp. (SGHN MA0633, holotype); A, lateral view; B, corresponding line drawing. Cross-hatching indicates the presence of a concretion. Scale bar: 10 cm.

the asymmetry is therefore less pronounced than in C. planirostris (ratio between 0.48 and 0.65, n = 15).

ffle anterior part of the vertex, including the ascending process of the premaxilla and the premaxillary crest, is overhanging the premaxillary sac fossae and the bony nares. fflis condition contrasts with C. planirostris , in which in lateral view the ascending process forms an angle of ≤ 90° with the horizontal plane of the skull, whereas the angle is> 90° in C. leidyi n. sp. ffle fairly slender premaxillary crest is anterolateraly directed. ffle right crest is distinctly larger than the left, as in C. planirostris . Maxilla

From a roughly vertical orientation on the anterior half of the rostrum, the lateral surface of the maxilla progressively shifts to a subhorizontal dorsal surface bordered by an acute lateral margin and the thick premaxilla medially. In this part, the dorsal side of the maxilla is covered with multiple, marked excrescences. Rostra of C. planirostris bear similar excrescences in the same area, usually less prominent than in the known specimens of C. leidyi n. sp.

On the lateral surface of the maxilla,a marked alveolar groove is visible which sharply slopes down from its uttermost point on the maxilla until approximately ⁹⁄₅ of the rostrum length. Within the groove SGHN MA0640 shows 12-13 very shallow alveoli probably corresponding to vestigial teeth. A few specimens of C. planirostris also show traces of shallow alveoli.

From the prominent maxillary tubercle, the maxilla forms a maxillary crest on the supraorbital process, with a roughly antero-posterior direction. fflis crest is less prominent than in C. planirostris , a feature especially noticeable in anterior view.

Each maxilla is pierced by two dorsal infraorbital foramina, one just behind the prominental notch, and the other lateral to the vertex.

Nasal ffle dorsal surface of the nasals is strongly worn in each specimen, but their outline is clearly discern-

able thanks to the conspicuous sutures with the premaxillary crests, frontals, and mesethmoid, with a condition similar to C. planirostris . In the latter the nasals are rarely preserved, and if preserved they show a more spongy aspect than surrounding bones. fflis is maybe the reason why they are easily damaged and lost in Choneziphius .

Frontal

Frontals are heavily worn on the vertex of the holotype and other referred specimens. However, judging from the short distance between the ascending processes of the maxillae, they were originally transversally narrower than the nasals, a condition similar to C. planirostris . ffle supraorbital process of the frontal is anteriorly bordered by the lacrimal and the maxilla.

Vomer

On the midline of the ventral side of the rostrum of the holotype, a narrow exposure of vomer is visible over a length of 166 mm, from a level 181 mm posterior to the apex of the rostrum.

Palatine ffle palatine is only partially preserved in the holotype. ffle anteriormost point of the maxilla-palatine suture is 115 mm anterior to the level of the antorbital notch. R EMARKS ffle most striking differences between C. leidyi n. sp. and C. planirostris are the general size and the rostrum length. fflerefore one has to wonder whether these differences (and the other differences) could be related to ontogeny and/or sexual dimorphism. Measurements of all available specimens of C. planirostris (all from the North Sea) show a mean rostrum length of 359 mm (n = 27, min = 297 mm, max = 416 mm), whereas C. leidyi n. sp. (from the Atlantic coast off Galicia) reports 499 mm (n = 2, min 495 mm, max 503 mm). It seems obvious that the large North Sea sample cannot be seen as a sexual dimorphic variant of the much larger Galician specimens. Indeed, variation within the North Sea sample (from very slender specimens to more robust specimens, see Lambert [2005: fig. 21]) shows all the aspects of sexual and/or ontogenetic variation within a same species.