A new beaked whale record from the upper Miocene of Menorca, Balearic Islands, based on CT-scan analysis of limestone slabs GIOVANNI BIANUCCI, SERGIO LLÀCER, JOSEP QUINTANA CARDONA, ALBERTO COLLARETA, and AGUSTÍ RODRÍGUEZ FLORIT Bianucci, G., Llàcer, S., Cardona, J.Q., Collareta, A., and Florit, A.R. 2019. A new beaked whale record from the upper Miocene of Menorca, Balearic Islands, based on CT-scan analysis of limestone slabs. Acta Palaeontologica Polonica 64 (2): 291–302. The finding of significant vertebrate remains inside commercial stone blocks is relatively rare. Here we describe a fossil cetacean skull discovered inside two slabs cut from a limestone block of Tortonian (i.e., early late Miocene) age from Menorca (Balearic Islands, Spain); this find represents the third record of a fossil cetacean from this island, as well as the best preserved. Unlike similar cases in the past, the Menorca skull was not extracted mechanically from the stone matrix, being rather imaged by means of computed tomography. The resulting 3D reconstruction of the skull allows us to refer the studied skull to the extant odontocete family Ziphiidae (beaked whales) and sheds light on the morphology of very delicate structures (e.g., the thin pterygoid hamuli and the mesorostral cartilage) that would likely have been destroyed during traditional mechanical preparation. This non-invasive investigation permits detailed osteo-anatomical compari- sons between the Menorca specimen and other extinct ziphiids, leading to the referral of the former to the stem beaked whale Messapicetus cf. longirostris. We then review the geographic distribution of fossil remains of Messapicetus, which include other occurrences from Tortonian shelf deposits of southeastern Italy, southern Peru, and Maryland (eastern USA). Early branching beaked whales (including basal members of the so-called “Messapicetus clade”) likely dispersed via the Central American Seaway, which allowed a direct communication between the Pacific and Atlantic oceans (in- cluding the Mediterranean cul-de-sac) throughout the Miocene. Ke y w o rd s : Mammalia, Cetacea, Ziphiidae, Messapicetus, palaeobiogeography, Neogene, Mediterranean, Spain. Giovanni Bianucci [giovanni.bianucci@unipi.it], Dipartimento di Scienze della Terra, Università di Pisa, via Santa Maria 53, 56126, Pisa, Italy. Sergio Llàcer [sergio.llacer@icp.cat], Institut Català de Paleontologia Miquel Crusafont, Universitat Autònoma de Barcelona, Carrer de les Columnes s/n, 08193 Cerdanyola del Vallès, Barcelona, Spain. Josep Quintana Cardona [picoguevo@gmail.com], Institut Català de Paleontologia Miquel Crusafont, Universitat Autònoma de Barcelona, Carrer de les Columnes s/n, 08193 Cerdanyola del Vallès, Barcelona, Spain; Carrer Gustau Mas 79, 1er, 07760 Ciutadella de Menorca, Illes Balears, Spain. Alberto Collareta [alberto.collareta@unipi.it], Dipartimento di Scienze della Terra, Università di Pisa, via Santa Maria 53, 56126, Pisa, Italy. Agustí Rodrígez Florit [a.rodriguez@geoservei.com], carrer Himàlaia 37, 07703 Maó, Illes Balears, Spain. Received 9 January 2019, accepted 12 February 2019, available online 23 April 2019. Copyright © 2019 G. Bianucci et al. This is an open-access article distributed under the terms of the Creative Commons Attribution License (for details please see http://creativecommons.org/licenses/by/4.0/), which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited. 1983; Hannibal and Davis 1992; Hannibal et al. 2008). Introduction Nevertheless, the finding of significant remains of verte- Fossils are rather frequently encountered inside stone brates inside commercial stone blocks is relatively rare, the blocks cut for commercial use. Indeed, lithotypes such few well-documented cases including the Middle Jurassic as the red ammonitic limestone or the Orthoceras lime- crocodylian Neptunidraco ammoniticus (Crocodylia, stone feature abundant fossil shells that often represent Metriorhynchidae) discovered in two slabs of red ammo- significant and appreciated decorative components of nitic limestone from northeaster Italy (Cau and Fanti 2011) the rock itself (e.g., Robinson and Bishop 1980; Wilson and the impressive record of marine vertebrate remains Acta Palaeontol. Pol. 64 (2): 291–302, 2019 https://doi.org/10.4202/app.00593.2019 292 ACTA PALAEONTOLOGICA POLONICA 64 (2), 2019 A C EUROPE Balearic Is. AFRICA B Ciutadella MENORCA Menorca 10 km Fig. 1. A. Geographical location of Menorca in the Mediterranean Sea (black arrow). B. Close-up of Menorca showing location of the Son Salord quarry (asterisk), where the Messapicetus MDM-2029 was found. The grey area indicates the extent of the upper Miocene (Tortonian–Messinian) carbonate deposits cropping out on the island. C. General view of the Son Salord quarry. The floor of the quarry roughly corresponds to the stratigraphic level where the fossil beaked whale was found. found in stone blocks and slabs of the Miocene limestone three-dimensional reconstruction of the skull obtained after “Pietra leccese” from southern Italy (e.g., Bianucci et al. processing of the scans proved to be extremely detailed 1994a, 2004; Bianucci 1996, 2001). In some cases, the study thanks to the good density contrast between the bone and of these fossils was preceded by a long and complex proce- surrounding matrix. In this way, it was possible to detail the dure for preparation, in a way to free the various parts of morphology of very delicate structures such as the thin pter- the bones from the embedding rock before reassembling ygoid hamuli and the mesorostral cartilage, which would the pieces preserved within different blocks or slabs. For probably have been destroyed during traditional mechanical example, the holotype of Zygophyseter varolai (Cetacea, preparation. This kind of non-invasive investigation allowed Physeteroidea), an almost complete skeleton, was reassem- us to refer the Menorca skull to a beaked whale, i.e., a bled from several large blocks of Pietra leccese after more member of the odontocete family Ziphiidae, whose fossil than five years of preparation work (Bianucci and Landini record is now well documented (Bianucci et al. 2016c and 2006). Similarly, the partial skeleton of Aegyptocetus tarfa references therein). In particular, the skull described here (Cetacea, Protocetidae) required preparation for one year is assigned to the genus Messapicetus, a stem ziphiid orig- to reassemble bone pieces from six slabs cut from a large inally described from the Tortonian of the Pietra leccese of block of middle Eocene nummulitic limestone from Egypt southern Italy (Bianucci et al. 1992, 1994b, 2016a), then ten- (Bianucci and Gingerich 2011). tatively recognised from the upper Miocene of the St. Marys Here we describe a late Miocene fossil cetacean skull Formation of Calvert Cliffs, Maryland, USA (Fuller and discovered inside two slabs cut from a commercial lime- Godfrey 2007), and later recorded with several specimens stone block extracted from the Son Salord quarry close to from upper Miocene beds of the Pisco Formation, Peru Ciutadella de Menorca (Menorca, Balearic Islands, Spain) (Bianucci et al. 2010, 2016b; Lambert et al. 2015; Di Celma and now kept in the Museu Diocesà de Menorca (Figs. 1, 2). et al. 2017; Ramassamy et al. 2018). This specimen represents the third record of a fossil ceta- cean from this island, as well as the best-preserved one. Institutional abbreviations.—ICP, Institut Català de Paleonto- In fact, cetacean remains from Menorca were previously logía Miquel Crusafont, Sabadell, Barcelona, Spain; MDM, documented only on the basis of two isolated teeth: (i) one Museu Diocesà de Menorca, Ciutadella de Menorca, Spain. tooth referred to “Scaldicetus grandis” from the Miocene of Illa de l’Aire, at the southeastern end of Menorca (Mercadal et al. 1985); and (ii) one tooth referred to an indeterminate Geological setting delphinid from the lower Tortonian of Torre d’en Penjat, at the southeastern coast of Es Castell (Mas et al. 2013). MDM-2029 was found in an area located about 2.5 km East The fossil cetacean from the Son Salord quarry was of Ciutadella de Menorca (Fig. 1A, B), where several lime- not extracted mechanically from the stone matrix; instead, stone quarries are located. The rock that is produced in these it was imaged by means of computed tomography. The quarries, locally known as “Mares”, is widely used for build- BIANUCCI ET AL.—MIOCENE BEAKED WHALE FROM BALEARIC ISLANDS 293 A1 A2 B1 B2 200 mm A3 A4 right mandible cranial cavity mandibular fossa nasal cavities vomer maxilla ossified presphenoid left mandible 5 0 mm Fig. 2. The two limestone slabs showing longitudinal cross sections of the Messapicetus cf. longirostris skull (MDM-2029) from the Tortonian of Menorca (Balearic Islands, Spain). A. Surface of slab 1 (A1, top; A2, bottom), details of A2 (A3, A4, explanatory drawing). B. Surface of slab 2 (B1, top; B2, bottom). ing purposes and is characterised by light colour, very porous Material and methods texture and a soft consistency (Sauleau 1985). In particular, MDM-2029 comes from the still-active quarry of Son Salord The fossil specimen studied herein is an incomplete cetacean (Fig. 1C), whose vertical walls display a rather massive and skull preserved within two limestone blocks of similar size homogeneous appearance, with more or less differentiated (ca. 400×450×140 mm) (Fig. 2). Although the two limestone and bioturbated beds. Macrofossils found at this quarry in- blocks are contiguous, there is a hiatus of ca. 11 mm between clude scarce rhodolits and fragments of red calcareous al- them, corresponding to the volume of rock lost during cut- gae, pectinid bivalves and irregular echinoids (belonging to the genera Clypeaster, Hypsoclypus, and Schizaster, among ting. CT segmentation of the skull was performed at Hospital others). According to official geological cartography, the Mateu Orfila (Mahón, Menorca) by using a medical scanner carbonate deposits exposed at the Son Salord quarry are (Philips Brilliance 16 CT scanner). The analytical conditions Tortonian (i.e., early late Miocene) in age (Rosell et al. 1989). of the CT-scan analysis are shown in Table 1. More recently, Pomar (2001), Pomar et al. (2002) and Mateu- The final processing of the images, which resulted in the Vicens et al. (2008) placed these sediments in their Lower 3D reconstruction of the cetacean specimen, was carried out Bar Unit, which is included in the lower Tortonian N16 zone at the ICP by using the software package AVIZO 7.1.0 (VSG, of the planktonic foraminiferal zonation of Blow (1969). The Table 1. Analytical conditions of the CT-scan analysis. ziphiid skull was found at a depth of 14 m below ground level, i.e., roughly at the level of the floor of the quarry as shown Slab 1 (top slab) Slab 2 (bottom slab) in Fig. 1C. It is unknown if it appeared in association with Pixel size 0.543 mm 0.621 mm other skeletal elements belonging to the same individual. It Interslice distance 1.5 mm 1.5 mm has not been possible to locate all the blocks in which other Number of slices 244 264 parts of the skull were preserved, because they were sold as Matrix of reconstruction 512 × 512 512 × 512 construction pieces before the specimen here described was Slice thickness 3 mm 3 mm recognised as a fossil vertebrate (Cristóbal Torres, personal Energy (peak kilovoltage) 120 kV 120 kV communication 2018). X-ray tube current 443 mA·s 375 mA·s 294 ACTA PALAEONTOLOGICA POLONICA 64 (2), 2019 endocranial cast A1 ossified falx A2 cerebri endocranial cast premaxilla frontal dorsal infraorbital foramina maxilla prenarial basin premaxillary dorsal sac fossa infraorbital maxillae foramina premaxillary foramina frontal right mandible jugal antorbital notch maxilla 100 mm left mandible right mandible skull endocranial cast left mandible mandibles filled internal nares pterygoid hamuli filled mesorostral canal including mineralised premaxilla vomer mesorostral cartilage 100 mm Fig. 3. 3D reconstruction resulting from the CT-scan of the ziphiid cetacean Messapicetus cf. longirostris Bianucci, Landini, and Varola, 1992 skull (MDM-2029) inside two limestone slabs from the Tortonian of Menorca (Balearic Islands, Spain), in dorsal (A1) and anterodorsal (A2) views. USA). The endocranial cavity, the choanae and the internal 1992 from the Tortonian beds of Cisterna quarry, near Lecce (southern oral cavity (mainly occupied by the larynx in the living an- Italy). imal), all filled with sediment, were also reconstructed and Messapicetus cf. longirostris Bianucci, Landini, and associated with the 3D model of the skull (Figs. 3–8). The skull was described on the basis of the CT-scan 3D Varola, 1992 reconstruction and CT-scan sections, integrated with direct Figs. 2–9. observations on the bones exposed on the cut surfaces of the Material.—MDM-2029, an incomplete skull (cranium and two limestone slabs. mandibles) preserved within two limestone slabs. The cra- Anatomical terminology follows Mead and Fordyce nium lacks most of the rostrum, the vertex area, the postero- (2009), except when explicitly stated otherwise. ventral walls of the braincase, the whole right squamosal, part of the left squamosal and all the ear bones. The two incomplete mandibular rami (of which only the posteroalve- Systematic palaeontology olar portions are preserved) are still in anatomical position with respect to the cranium. From lower Tortonian N16 Cetacea Brisson, 1762 (Miocene), 2.5 km East of Ciutadella de Menorca, Spain. Odontoceti Flower, 1867 Description.—Premaxilla: In dorsal view, the premaxilla Ziphiidae Gray, 1850 appears as transversely narrow on the preserved portion of the rostrum, whereas it widens abruptly posterior to the an- “Messapicetus clade” (sensu Bianucci et al. 2016) torbital notch (Fig. 3). The medial margins of the premaxillae Genus Messapicetus Bianucci, Landini, and Varola, do not contact each other, reaching the maximum distance of 1992 27 mm ca. 100 mm anterior to the base of the rostrum. The Type species: Messapicetus longirostris Bianucci, Landini, and Varola, transverse sections of the rostrum indicate that the premax- BIANUCCI ET AL.—MIOCENE BEAKED WHALE FROM BALEARIC ISLANDS 295 premaxilla A1 A2 maxilla pterygoid hamulus prenarial basin A3 A4 filled mesorostral canal including mineralised skull pterygoid hamuli vomer mesorostral cartilage Fig. 4. 3D reconstruction resulting from the CT-scan of the ziphiid cetacean Messapicetus cf. longirostris Bianucci, Landini, and Varola, 1992 skull (MDM-2029) inside two limestone slabs from the Tortonian of Menorca (Balearic Islands, Spain); in anterior view, showing transverse cross sections of the rostrum (A1–A4) made at different distances from the rostrum base. Not to scale. illae are clearly thickened and more dorsally convex than the the right and left maxilla. Indeed, on the right maxilla, there maxillae close to the anterior end of the preserved portion are three large foramina located from 5 to 22 mm anterior to of the rostrum, whereas they are thin and dorsally exca- the antorbital notch and at least two large foramina located vated near the base of the rostrum (Fig. 4). This proximal from 23 to 62 mm posterior to the antorbital notch; in turn, excavation of the rostral portion of the premaxillae, further on the left maxilla, only one of the five foramina located emphasised by the lateral thickening of the maxillae (form- near the antorbital notch is large in size, whereas two large ing a prenarial basin sensu Lambert 2005), is also clearly foramina are located, close to each other, 60–70 mm poste- visible in dorsal and anterodorsal views of the cranium. The rior to the antorbital notch. Posterior to the antorbital notch, premaxillary sac fossae are weakly asymmetrical, with the the thin ascending process of the maxilla almost completely right fossa being slightly transversely wider than the left (ra- covers the frontal. No trace of a maxillary crest is observed tio between the widths of the left and right premaxillary sac on the lateral margin of the ascending process of the max- fossae = 0.77). At least three small foramina are visible near illa. Just anterior to the nares, a narrow strip of the maxilla is the anterolateral margin of the right premaxillary fossa, the apparently exposed medial to each premaxilla. On the pala- anteriormost one being located 18 mm anterior to the corre- tal surface of the maxillae, there is no trace of dental alveoli sponding antorbital notch. It is not clear whether one of these or an alveolar groove, indicating that no teeth were present foramina might represent the main premaxillary foramen. in the posteriormost portion of the rostrum, until a level at Maxilla: The maxilla is widely exposed on the dorsal sur- least 160 mm anterior to the antorbital notches (Fig. 5). The face of the rostrum, being transversely wider than the pre- ventral infraorbital foramen is visible on the posteromedial maxilla for all the preserved portion of the rostrum (Fig. 3). surface of the maxilla. The lateral margin of the preserved rostral portion of the Frontal: In dorsal view, the frontal is almost totally cov- maxilla rises progressively toward the antorbital notch, ered by the ascending process of the maxilla, being visible thus forming an elevated rostral maxillary crest, which is for a narrow extension, located at the lateral margin of the also clearly visible in the transverse sections of the rostrum orbit and, with a small portion, posterolateral to the na- (Fig. 4). This crest does not extend posterior to the antorbital res (Fig. 3). In lateral view, the preorbital and supraorbital notch in the supraorbital region. Clusters of large (5–9 mm processes are dorsoventrally thin, whereas the postorbital wide) and small (2–3 mm) dorsal infraorbital foramina are process is triangular, with a wide ventral tip that points visible on both maxillae, both anterior and posterior to the posteroventrally (Figs. 6, 7). The orbit is anteroposteriorly antorbital notches. Their size and position are different on elongated. On the ventral surface of the skull, the frontal is 296 ACTA PALAEONTOLOGICA POLONICA 64 (2), 2019 A1 right mandible filled internal nares and internal oral cavity left mandible 100 mm A2 frontal antorbital notch maxilla pterygoid hamulus vomer skull mandibles infraorbital foramen pterygoid hamuli jugal vomer anterior portion of jugal endocranial cast zygomatic 100 mm filled internal nares and process posterior portion of jugal orbit internal oral cavity Fig. 5. 3D reconstruction resulting from the CT-scan of the ziphiid cetacean Messapicetus cf. longirostris Bianucci, Landini, and Varola, 1992 skull (MDM- 2029) inside two limestone slabs from the Tortonian of Menorca (Balearic Islands, Spain); in ventral view (A1), ventral view without the mandibles (A2). widely exposed, forming the dorsal roof of the orbit and of scan reconstruction of the dorsal surface of the skull (Fig. 3) the temporal fossa (Fig. 5). and the CT cross sections of the rostrum (Fig. 4) highlights Presphenoid and vomer: On the cut surface of the two a dorsal relief at the middle of the mesorostral canal that slabs, a section of the ossified nasal septum is observed could represent the mineralised mesorostral cartilage (i.e., (Fig. 2A3, A4); it is formed by the ossified presphenoid and, cartilaginous nasal septum), perhaps in origin partially os- laterally, by the vomer. Anterior to the nasal septum, the sified. The vomer extends anterior to the nasal septum, mesorostral canal is filled internally by sediment, as also forming a narrow and elevated keel that is visible in ventral confirmed by the CT-scan, showing that this region of the view in a narrow fissure between the medial margins of the slabs has density values lower than in the surrounding areas pterygoids (Fig. 5). The vomer is not pachyostotic and does formed by dense maxillae (Fig. 8). Nevertheless, the CT- not fill the mesorostral canal. BIANUCCI ET AL.—MIOCENE BEAKED WHALE FROM BALEARIC ISLANDS 297 A1 endocranial cast right mandible 100 mm rostral maxillary crest A2 premaxilla antorbital notch maxilla pterygoid hamulus 100 mm filled internal nares and internal oral cavity A3 skull mandibles pterygoid hamuli vomer transverse crests filled mesorostral canal endocranial cast 20 mm filled internal nares and internal oral cavity Fig. 6. 3D reconstruction resulting from the CT-scan of the ziphiid cetacean Messapicetus cf. longirostris Bianucci, Landini, and Varola, 1992 skull (MDM-2029) inside two limestone slabs from the Tortonian of Menorca (Balearic Islands, Spain); in right lateral view (A1), right lateral view without the mandibles (A2), detail of the pterygoid hamuli showing the well-preserved transverse crests (A3). Jugal and lacrimal: The anterior process of the jugal is Pterygoid: The hamular process of the pterygoid is large, dorsally exposed, forming a distinct tubercle between the an- extending anteriorly onto the palatal surface of the ros- torbital notch and the antorbital process of the frontal (“lateral trum for ca. 110 mm from the antorbital notch and ventrally process” sensu Lambert et al. 2013) (Fig. 3). The preserved covering the wide pterygoid sinus fossa at its anterior end anterior and posterior portions of the styliform process of the (Fig. 5). Together, the posterior margins of the hamular left jugal are slender (Fig. 7). In ventral view, the suture be- processes form a medial point that is posteriorly directed (a tween the jugal and the lacrimal is not clearly visible (Fig. 5). plesiomorphic condition that is absent in all other ziphiids Compared to the anteroposterior length of the orbit, the an- for which this feature is known). Nevertheless, it is possible teroposterior extension of the lacrimojugal complex is small. that this shape is due to the fact that the posterolateral por- 298 ACTA PALAEONTOLOGICA POLONICA 64 (2), 2019 A1 left mandible 100 mm A2 rostral maxillary crest maxilla orbit endocranial cast filled internal pterygoid hamulus oral cavity 100 mm squamosal A3 jugal antorbital process postorbital process skull anterior portion of jugal mandibles pterygoid hamuli vomer endocranial cast posterior portion of jugal filled internal nares 20 m m zygomatic process and internal oral cavity Fig. 7. 3D reconstruction resulting from the CT-scan of the ziphiid cetacean Messapicetus cf. longirostris Bianucci, Landini, and Varola, 1992 skull (MDM-2029) inside two limestone slabs from the Tortonian of Menorca (Balearic Islands, Spain); in left lateral view (A1), left lateral view without the mandibles (A2), detail of the orbital area (A3). tions of the hamular processes are missing or too delicate to Mandible: The dorsal surface of the preserved poste- be imaged by means of CT-scan analyses. As in Ninoziphius rior portion of the right mandible (which is more complete platyrostris and in a few skulls of extant ziphiids (Lambert than the left) does not exhibit hints of either distinct den- et al. 2013), the inner surface of the hamular process is tal alveoli or an alveolar groove, thus suggesting that the crossed by clearly distinct transverse crests (Fig. 6A3). dentigerous portion of the bone is completely missing. In Squamosal: The sections of both zygomatic processes of lateral view, the dorsal margin is weakly concave, with an the squamosals are exposed on one of the cut slab surfaces anteroposteriorly elongated coronoid crest anteriorly limited (Fig. 2B2). The left zygomatic process, partially reconstructed by a precoronoid crest located 21 mm anterior to the pos- using the CT-scans, appears short and directed anterodor- terior end of the mandibular condyle (Fig. 9A2). Posterior sally. Its anterior apex articulates with the posterior preserved to the precoronoid process, the coronoid crest slopes down portion of the styliform process of the jugal (Figs. 5, 7). progressively towards the coronoid process, which is conse- BIANUCCI ET AL.—MIOCENE BEAKED WHALE FROM BALEARIC ISLANDS 299 quently lower than the precoronoid process. The mandibular A B condyle is protuberant, being ventrally separated from the angular process by a deep posterior notch. The mandibular foramen extends for more than 20 cm anterior to the poste- rior end of the mandibular condyle (Fig. 9A4). Remarks.—The Menorca skull exhibits a clear ziphiid syn- apomorphy: the wide hamular fossa of the pterygoid sinus, C 1500 Gray value extending anterior to the antorbital notch onto the palatal sur- 1000 face of the rostrum (Lambert et al. 2013; Bianucci et al. 2016c: 500 character 35, state 1). Moreover, among odontocetes, trans- 0 verse crests on the inner surface of the hamular process are only known for a few ziphiid species (Lambert et al. 2013). 0 20 40 60 80 100 120 Distance (mm) Among ziphiids, MDM-2029 shares with all the members of the “Messapicetus clade” (sensu Bianucci et al. 2016c, includ- Fig. 8. CT-scan of the ziphiid cetacean Messapicetus cf. longirostris Bia- ing also Dagonodum; Ramassamy 2016) except Notoziphius nucci, Landini, and Varola, 1992 skull (MDM-2029) inside two limestone the thickening of the compact premaxillae (pachyosteoscle- slabs from the Tortonian of Menorca (Balearic Islands, Spain). A. Transverse section of the rostrum. B. Dorsal outline of the cranium showing the posi- rosis) along the rostrum (Bianucci et al. 2016c: character 30, tion of the section. C. Variation of the gray-value density along the trans- states 1–3). Within the Messapicetus clade, MDM-2029 shares verse section of the rostrum. with Aporotus, Beneziphius, Dagonodum, Messapicetus, and Ziphirostrum another derived character: the presence of a 2005). Aporotus and Beneziphius differ from MDM-2029 by prenarial basin bounded laterally by a thick stripe of the max- the greater thickening of the premaxillae along the rostrum illa (comparison with Ziphirostrum is based on Ziphirostrum (Bianucci et al. 2016c: character 30, state 2). Aporotus further marginatum, the best-known of the three species included differs from MDM-2029 by having a rostral maxillary crest in this genus, as well as the only one for which a specimen that extends posteriorly on the antorbital process, thus de- with precise stratigraphic provenance is known; Lambert limiting a wide and deep dorsal depression (Lambert 2005). A1 A 2 coronoid process coronoid crest mandibular condyle posterior notch 100 mm precoronoid crest A3 A4 mandibular coronoid crest mandibular condyle condyle mandibular foramen 100 mm Fig. 9. CT-scan 3D reconstruction of the posterior portion of the left mandible of the ziphiid cetacean Messapicetus cf. longirostris Bianucci, Landini, and Varola, 1992 skull (MDM-2029) inside two limestone slabs from Tortonian of Menorca (Balearic Islands, Spain); in anterior (A1) lateral (A2) posterior (A3), and medial (A4) views. 300 ACTA PALAEONTOLOGICA POLONICA 64 (2), 2019 MDM-2029 Messapicetus longirostris Messapicetus gregarius Ziphirostrum marginatum Fig. 10. Comparison of the dorsal view of the preserved cranium of Messapicetus cf. longirostris (MDM-2029) with some stem beaked whales. The dotted ovals indicate the extent of the prenarial basin. Beneziphius further differs from MDM-2029 by its joined (206–230 mm) and in the range of Messapicetus gregarius premaxillae that limit anteriorly the prenarial basin and by (163–210 mm), but consistently larger than in Z. marginatum the dorsal surface of maxilla being horizontal lateral to the (roughly 100 mm); (ii) the posteroalveolar portion of the prenarial basin (Lambert 2005). Therefore, with respect to rostrum is at least 160 mm long in MDM-2029, close to M. MDM-2029, Dagonodum, Messapicetus, and Ziphirostrum longirostris (180 mm) and M. gregarius (150–255 mm), but appear as the closest genera. Interestingly, all the fossils re- consistently larger than in Z. marginatum (roughly 100 mm) ferred to Messapicetus spp., the holotype and only known (Fig. 10). specimen of Dagonodum mojnum, and the only Ziphirostrum Finally, the aforementioned absence of a distinct max- marginatum skull for which precise information about the illary tubercle and of a prominential notch, coupled with stratigraphical provenance is known come from Tortonian the presence on the right maxilla of a cluster of two-three strata, as does the Menorca skull. dorsal infraorbital foramina (contra only one foramen in Although comparisons between MDM-2029 and the M. gregarius; Bianucci et al. 2016a), also facilitates attri- sole known specimen Dagonodum are complicated by the bution of MDM-2029 to M. longirostris rather than to M. fragmentary status of both skulls, clear differences reside gregarius. Consequently, MDM-2029 is most closely related in the shape of the posterior portion of the rostrum, as to Messapicetus longirostris, both the former and the lat- Dagonodum exhibits a well-developed maxillary tubercle ter being found in Tortonian deposits of the Mediterranean and associated prominential notch that is absent in MDM- basin. Indeed, there is a good overlap in size and shape 2029. Messapicetus and Ziphirostrum marginatum are very between MDM-2029 and M. longirostris; moreover, several similar to each other, differing essentially for the degree preserved portions of the Menorca skull appear to be very of elongation of the rostrum—a feature that is not useful similar to the corresponding features in M. longirostris (e.g., for comparisons with the Menorca skull, which only pre- the shape of the rostral maxillary crest, the slender antorbital serves the posterior portion of the rostrum. Nevertheless, process, the thin supraorbital process, the anteroposteriorly two characters, possibly related to the degree of elongation elongated coronoid crest of the mandible and the protuberant of the rostrum, attribute MDM-2029 to Messapicetus rather mandibular condyle). The only substantial differences be- than to Z. marginatum: (i) the length of the dorsally open tween the Menorca skull and Messapicetus longirostris (and posterior portion of the mesorostral groove is at least 180 also M. gregarius) is the more anteroposteriorly elongate mm in the Menorca skull, close to Messapicetus longirostris orbit (Table 2) and the greater dorsoventral thickening of the Table 2. Cranial measurements (in mm) of Messapicetus cf. longirostris from the Tortonian of Spain (MDM-2029), Messapicetus longirostris from Italy, and Messapicetus gregarious from Peru. Asterisk indicates doubling of measurement from one side. MDM-2029 Messapicetus longirostris Messapicetus gregarius Width of rostrum base at level antorbital notch 203 190* 203–217 Width of premaxillae at level antorbital notch 105 80–109 Preorbital width of skull 300 296–313 Postorbital width of skull 346* 323–352 Length of orbit 113 88 80–88 Total width of premaxillary sac fossae 140 136–142 Maximum width of right premaxillary sac fossa 60 59–67 Maximum width of left premaxillary sac fossa 46 47–58 Length of left pterygoid hamulus 170 195 Condylar width +106 110–120 Bizygomatic width +335? 310–313 BIANUCCI ET AL.—MIOCENE BEAKED WHALE FROM BALEARIC ISLANDS 301 lateral margin of the preserved rostral portion of the maxilla the Pietra leccese of southern Italy (Bianucci et al. 1992, (Figs. 3A2, 4). The first difference could partly be due to 1994b, 2016a); all these occurrences (Fig. 11) take place in some inaccuracy in the CT-scan 3D reconstruction, whereas shelf deposits of Tortonian (i.e., early late Miocene) age. the different degrees of thickening of the maxilla could be Interestingly, Messapicetus and the two earliest branching due to intraspecific ontogenetic variation. Nevertheless, con- stem ziphiids Chavinziphius and Ninoziphius are known sidering also the incompleteness of MDM-2029, we prefer to from the Pisco Formation, suggesting a dispersal route refer this specimen to Messapicetus cf. longirostris, pending running between the southeastern Pacific and the eastern the discovery of more complete material. Mediterranean for early beaked whales. Such a distributional pattern was possible since the Central American Seaway allowed a direct communication between the Pacific and Palaeobiogeography Atlantic oceans in late Miocene times (Jacobs et al. 2004; Bianucci et al. 2010, 2016a). Among extant toothed whales, beaked whales are likely the most enigmatic family, due to their deep-sea habits and elu- sive behaviour. Scanty and fragmentary until a few decades Conclusions ago, the fossil record of Ziphiidae is now rich in taxa and well documented, thanks to recent research on specimens We describe a beaked whale skull discovered inside two slabs from phosphorite layers cropping out on the bottom of deep cut from a commercial block of upper Miocene limestone oceanic areas and from inland deposits, notably the Pisco from Menorca (Balearic Islands, Spain). This specimen was Formation of Peru (Lambert et al. 2009, 2010, 2013, 2018; not freed mechanically from the entombing stone, but rather Bianucci et al. 2010, 2016a, c; Ichishima et al. 2017). A recent was imaged by means of computed tomography. The re- phylogenetic and biogeographical analysis (Bianucci et al. sulting three-dimensional reconstruction of the skull proved 2016b) recognised two major clades among Ziphiidae char- extremely detailed and pivotal for resolving the morphol- acterised by a high degree of diversity and disparity during ogy of very delicate structures (probably including the only the late Miocene: (i) the so-called Messapicetus clade, which partly ossified mesorostral cartilage) that would probably dominated the North Atlantic and went extinct during the have been destroyed during traditional mechanical prepa- Pliocene; (ii) crown Ziphiidae, most of which inhabited the ration. Messapicetus shows a geographic distribution from Southern Ocean and subsequently dispersed globally. Both Tortonian shelf deposits of Italy, Peru, and the Eastern USA. clades apparently followed similar evolutionary trends, in- Early branching beaked whales (including basal members of cluding an increase in the compactness and thickness of the the so-called “Messapicetus clade”) likely dispersed via the rostrum, the loss of functional teeth, and an increase of body Central American Seaway, which allowed for faunal inter- size, possibly related to a convergent ecological shift from change between the southeastern Pacific and the northern ancestral epipelagic and raptorial trophic habits to suction Atlantic/Mediterranean realms until latest Miocene times. feeding in deep waters (Lambert et al. 2015; Bianucci et al. 2016c). In this evolutionary and biostratigraphic scenario, the geographic distribution of Messapicetus, the basal most member of the Messapicetus clade, is remarkable. In fact, Acknowledgements this genus was recorded from the Pisco Formation of Peru The authors want to express their gratitude to the following people and (Bianucci et al. 2010, 2016b; Lambert et al. 2015; Di Celma institutions, whose help made this study possible. Thanks are especially et al. 2017; Ramassamy et al. 2018); it was tentatively rec- due to owner of the Son Salord quarry, Cristobal Torres (Ciutadella de ognised from the St. Marys Formation of Maryland, USA Menorca, Spain), who discovered and brought to our attention the skull here described, for facilitating its study at all times. Thanks also to the (Fuller and Godfrey 2007); it is here reported for the first management of the Hospital Mateu Orfila (Maó, Menorca) for allow- time in Menorca, Spain; and it was first described from ing the use of their CT service, which provided the images on which this work is based. The technical assistance of Marina Febrer Febrer (specialist doctor in radiodiagnosis) and Pedro Delgado Cantero (tech- Messapicetus nician in radiodiagnosis), both at the Hospital Mateu Orfila, allowed cf. longirostris us to obtain these images. This project was carried out, to a large ex- cf. Messapicetus sp. Messapicetus tent, thanks to the institutional support of Salvador Moyà-Solà, former longirostris director of the ICP. Logistical support from Miquel Fernández (Maó, Spain) and Josep Lluis Florit (Consell Insular de Menorca, Spain) was essential for moving the specimen to the Hospital Mateu Orfila. Antoni Messapicetus Obrador (Universitat Autonoma de Barcelona, Spain) collaborated in gregarius the interpretation of the geological context in which the specimen was found. We are sincerely indebted to Stephen J. Godfrey (Calvert Marine Museum, Solomons, USA), Pavel Gol’din (I.I. Schmalhausen Fig. 11. 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