Globicetus hiberus, 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 : 124-130

Globicetus hiberus n. sp.

( Figs 10-13 ; Table 3)

HOLOTYPE. — ML 1361, partial skull including rostrum, facial area and vertex.

REFERRED SPECIMENS. — MHNUSC 3958 , partial skull including facial area and vertex, 20 miles from Touriñán Cape, off the Galician coast, depth of 1500 m, 42°50’N, 9°40’W ; IEO DR26 026, partial skull including rostrum and anterior portion of facial area, off the Galician coast, depth of approximately 1500 m, 42°27’N, 11°59’W .

ETYMOLOGY. — From Latin “hiberus”, Iberian, for the geographical origin of the holotype and referred specimens.

TYPE LOCALITY. — South of Nazaré Canyon off the Portuguese coast, exact locality unknown, but likely around 39°18’N, 9°47’W.

DIAGNOSIS. — Globicetus hiberus n. gen., n. sp. differs from all other ziphiids in the large spherical medial rostral prominence formed by the fused premaxillae, in the large prominence of the right premaxilla anterior to the right premaxillary sac fossa, and in the barely marked antorbital notch, related to the important widening of the rostrum base.

Among the other ziphiine genera it further differs from Ziphius and Izikoziphius in the medial fusion of the premaxillae closing the mesorostral groove; it shares with Imocetus n. gen. and Tusciziphius the anterior part of the nasal contacting the premaxillary crest and the extreme ossification and fusion of the vertex elements, but it differs from Imocetus n. gen. in lacking a wide facial depression, rostral maxillary spur-shaped crest, and in having the premaxillary foramina not located posterior to the level of the antorbital notch; it differs from Tusciziphius in the less transversally expanded vertex (lower width between the premaxillary crests, and lower distance between maxillae posterior to the vertex), and in the posterolateral direction of the right premaxillary crest. It further differs from the possible ziphiine Caviziphius in shallower excavation of the premaxillary sac fossae.

DESCRIPTION ffle skull is slightly smaller than in the largest specimens of Imocetus piscatus n. gen., n. sp. (see below), with a postorbital width estimated at 372 mm in the holotype. ffle rostrum is elongated and its base is wide. ffle posterior half of the rostrum is characterized by the extreme thickening of the premaxillae, forming a large spherical prominence followed towards the right premaxillary sac fossa by a high shelf (see below). ffle facial area is short with the low and wide vertex overhanging it, hiding the bony nares and most of the premaxillary sac fossae in dorsal view.

Premaxilla

On the roughly complete rostrum of the holotype the premaxilla is slightly longer apically (20 mm) than the maxilla.On the anterior half of the massive and subcylindrical rostrum, the mesorostral groove is dorsally closed by the thick premaxillae, displaying a medial sutural contact. In dorsal view, the posterior half of the rostrum is partly covered by a large, roughly spherical, element made by the joined premaxillae. Preserved on the holotype and IEO DR26 026, this unusual prominence has a maximum width of 150 mm and 141 mm respectively in these two specimens and a maximum height above the maxilla of 135 mm and 92 mm. It is slightly asymmetrical, higher on the right side of the holotype and longer on the right side of IEO DR26 026. It is made, at least superficially, by compact bone, covered with narrow and shallow anastomosed sulci likely related to vascularization.On the holotype, the anterior and anterolateral margins of the spheroid do not contact the underlying premaxilla and maxilla, leaving an open space of about 10 mm, whereas in IEO DR26 026 a high medial pad of bone joins the spheroid to the dorsal surface of the rostrum. Posteriorly, the spheroid is followed by a thick shelf predominantly constituted by the right premaxilla, whose surface is similarly compact and covered with sulci. Rectangular in dorsal view in the holotype, this shelf is distinctly narrower distally in IEO DR26 026 and in the anteriorly incomplete skull MHNUSC 3958. In lateral view the dorsal margin of the shelf of the latter raises forwards similarly to the more complete specimens, suggesting the presence of a similar large spheroid in MHNUSC 3958. ffle abrupt posterior margin of the shelf corresponds to the anterior limit of the right premaxillary sac fossa, which is considerably wider than the left fossa. Only a narrow and much lower longitudinal crest is located anterior to the left premaxillary sac fossa of the holotype and MHNUSC 3958. Both fossae are short anteriorly, more than in Tusciziphius , nearly completely dorsally overhung by the vertex. ffle presence of the massive shelf in Globicetus n. gen., associated with shorter premaxillary sac fossae, might be interpreted as an overgrowth of the thickened anterior portion of the right premaxillary sac fossa observed in T. atlanticus n. sp. ffle surface of the premaxillary sac fossae is strongly concave and no premaxillary foramen could be detected on the bottom of any of the fossae.Only one foramen is observed on the medial margin of the left fossa of the three specimens, similar to the condition in Choneziphius leidyi n. sp., Imocetus n. gen., and T. atlanticus n. sp.

ffle ascending process of each premaxilla is strongly constricted and short. On the low vertex, the over - hanging right premaxillary crest is much wider than the left, reaching laterally a level beyond the lateral margin of the corresponding premaxillary sac fossa. ffle top of the vertex is made by the right premaxilla, much higher than the left. ffle anterior margin of the right premaxillary crests is posterolaterally directed, whereas the anterior margin of the left premaxillary crest is roughly anterolaterally directed. In Tusciziphius both crests are usually anterolaterally directed.

Maxilla

Apically invisible in dorsal view, the maxilla only slightly widens along the distal half of the rostrum, with a somewhat medially convex maxilla-premax - illa suture. From the level of the large spheroid it sends a thin lateral plate whose lateral margin reaches the preorbital process in a nearly rectilinear line, forming a wide rostrum base. Differing from T. atlanticus n. sp. and Imocetus n. gen., the antorbital notch is therefore barely individualized; a wide subhorizontal surface margins the premaxillary shelf on both sides of the rostrum base. fflis surface is pierced by several dorsal infraorbital foramina, three on the right side and two on the left side of the holotype, one less on the right side of MHNUSC 3958, and one less on each side of IEO DR26 026. From these foramina, several sulci are sent anteriorly and anterolaterally. A large longitudinal sulcus passes between the spheroid of the premaxillae and the maxilla, exiting on the anterior margin of the spheroid.

On the supraorbital area, the maxilla is thin, lacking any maxillary crest contrary to part of the specimens of T. atlanticus n. sp. and Imocetus n. gen. Posterior to the nasals on the vertex, left and right maxillae are close to each other, more than in Tusciziphius , with a minimal distance between the maxillae lower than the width of the nasals. At this level the medial margin of the right maxilla is more erected than the margin of the left maxilla; the latter is the continuation of the depressed dorsal surface of the nasals.

On the ventrolateral surface of the rostrum, the remnant of alveolar groove does not contain individualized alveoli.

Nasal

Excluded from the premaxillary crest, the nasal is considerably narrower anteriorly than posteriorly. ffle dorsal surface of the joined nasals forms a depression between the premaxillary crests, as in Imocetus n. gen. and Tusciziphius . ffle anterior tip of the nasals does not reach a level anterior to the premaxillary crests, differing from Izikoziphius and Ziphius . ffle medial suture is distinctly shifted to the left side compared to the sagittal plane of the skull.

Frontal

Only parts of the frontal are preserved on the heavily worn supraorbital area. Frontals are lost on the vertex; they apparently originally formed an anteromedial projection between nasals.

Vomer

Hidden dorsally by the development of the premaxillae, the vomer is only visible ventrally between the premaxillae and between the maxillae. At the rostrum base, its ventral exposure between the maxillae of the holotype is likely due to partial wear of the latter and loss of the palatines.

Palatine

Most parts of the palatine are likely lost in the three specimens.A large depression with a distinct outline marks the original anterior extent of the palatine on the rostrum, far anterior from the antorbital notch. ffle palatine was longer in IEO DR26 026, reaching a level 315 mm anterior to the notch.

Lacrimal ffle lacrimal is only partly preserved ventral to the maxilla on the preorbital process of the holotype. Its ventral exposure appears rather narrow but its original extension cannot be estimated due to the bad preservation of the ventral surface of the skull.

REMARKS

A series of arguments support the interpretation of the conspicuous spheroid at the rostrum base of Globicetus hiberus n. gen., n. sp. as a non-pathological element. First, it is present with a very similar outer shape in two of the described specimens. it has also been observed by us in additional undescribed skulls kept in private collections, and its presence is very likely in the third described specimen. In addition, from a morphological point of view, it is nearly symmetrical, with smooth surfaces contrasting with different kinds of pathological bone growths. Furthermore, canals for vascularization/innervation at the base of the spheroid are not interrupted. Finally no fracture or pathological bone tissue has been detected ventral to the spheroid in any of the described specimens.

From a systematic point of view, a dorsomedial sutural contact between the premaxillae is observed on the rostrum of part of the ziphiines ( Choneziphius , Imocetus n. gen., and Tusciziphius ) and members of the “ Messapicetus clade”. ffle general morphology of the low and wide, trapezoidal, extremely ossified, and strongly asymmetric vertex, overhanging the bony nares and the premaxillary sac fossae, closely resembles Tusciziphius and, in a lesser extent, Imocetus n. gen. A superficially similar morphology is also observed in the hyperoodontine Hyperoodon , but in this case the nasal is deeply thrusted in the premaxillary crest and the left premaxillary crest is distinctly directed posterolaterally. ffle development of a high medial prominence of the joined premaxillae on the rostrum is similarly observed in some specimens of Tusciziphius atlanticus n. sp. and in a fragmentary skull referred here to aff. Caviziphius sp. (see below). In none of these specimens the prominence displays a spherical volume shape. Additional differences with Tusciziphius are: large prominence of the right premaxilla anterior to the right premaxillary sac fossa; barely marked antorbital notch, related to the important widening of the rostrum base; less transversally expanded vertex (lower width between the premaxillary crests and lower distance between the maxillae posterior to the vertex); and posterolateral direction of the right premaxillary crest.

Figures

FIG. 10.— Skull of Globicetus hiberus n. gen.,n.sp.(ML 1361,holotype):A, dorsal view;B, corresponding line drawing.Scale bar:10 cm.

FIG. 11. — Skull of Globicetus hiberus n. gen., n. sp. (ML 1361, holotype): A, lateral view; B, corresponding line drawing; C, anterodorsal view; D, corresponding line drawing. Scale bar: 10 cm.

FIG. 12. — Skull of Globicetus hiberus n. gen., n. sp. (ML 1361, holotype): A, ventral view; B, detail of the facial area in anterior view; C, anterolateral view; D, corresponding line drawing. Scale bar: 10 cm.

FIG. 13. — A-C, partial skull of Globicetus hiberus n. gen., n. sp. (MHNUSC 3958): A, dorsal view; B, lateral view; C, detail of the vertex and premaxillary sac fossae in anterior view; D-F partial skull of G. hiberus n. gen., n. sp. (IEO DR26 026); D, dorsal view; E, lateral view; F, detail of the spherical premaxillary prominence in anterior view. Parallel lines indicate a break surface. Scale bar: 10 cm.