BULLETIN DE L’INSTITUT ROYAL DES SCIENCES NATURELLES DE BELGIQUE SCIENCES DE LA TERRE, 77: 197-210,2007 BULLETIN VAN HET KONINKLIJK BELGISCH INSTITUUT VOOR NATUURWETENSCHAPPEN AARDWETENSCHAPPEN, 77: 197-210,2007 A monodontid cetacean from the Early Pliocene of the North Sea by Olivier LAMBERT & Pierre GIGASE L a m b e r t O. & G ig a s e P., 2007 -A monodontid cetacean from fosse temporale est plus élevée que chez D. leucas et le rostre the Early Pliocene of the North Sea. Bulletin de I ’Institut royal des ne comporte pas la paire de dents maxillaires modifiées de M. Sciences naturelles de Belgique, Sciences de la Terre 77: 197-210, monoceros. Plusieurs sillons observés à la surface des os crâniens 9 figs, 2 tables, Brussels, October 15,2007 - ISSN 0374-6291. sont interprétés comme des marques de dents de requin, résultant soit d’un épisode de prédation, soit de l’action d’un charognard. Plusieurs os de l’oreille isolés du Néogène d’Anvers sont Abstract également attribués à un Monodontidae. Les nouveaux spécimens décrits ici indiquent que des membres de cette famille ont migré A partial skeleton from the Early Pliocene of Antwerp (north of vers des eaux plus froides avant ou durant le Pliocène précoce, Belgium), including a fragmentary skull, corresponds to the first bien avant les premières mentions pléistocènes de Delphinapterus record of a fossil member of the family Monodontidae in the North leucas dans la Mer du Nord. De plus, la paléobiogéographie des Sea. The vertex of the skull is lower than in the oldest known Delphinidae, Monodontidae et Phocoenidae fossiles suggère une Monodontidae, the latest Miocene Denebola brachycephala, and the origine pacifique pour les ‘crown-Delphinoidea’ de l’Atlantique orbit is more anteriorly shifted. It differs from the two extant species Nord. of the family, the beluga Delphinapterus leucas and the narwhal Monodon monoceros, among others, in a shorter orbit and a shorter Mots-clefs: bélouga, narval, Monodontidae, Pliocène, Mer du and wider antorbital notch. The anterior part of the temporal fossa is Nord, paléobiogéographie. more elevated than in D. leucas and the rostrum lacked the modified pair of maxillary teeth of M. monoceros. Grooves observed at the surface of the skull bones are identified as shark teeth marks, either Introduction the result of a predation event or of scavenging. Several isolated ear bones from the Neogene of Antwerp are similarly referred to Monodontidae. The new specimens described The family Monodontidae includes two extant here imply that members of the family migrated towards colder monospecific genera: the beluga Delphinapterus water before or during earliest Pliocene, well before the first leucas (PALLAS, 1776) and the narwhal Monodon Pleistocene records of Delphinapterus leucas in the North Sea. monoceros L in n a e u s , 1758, both geographically The palaeobiogeography of fossil Delphinidae, Monodontidae and Phocoenidae further suggests a Pacific origin for the crown- restricted to the cold Arctic Ocean and adjoining Delphinoidea of the North Atlantic realm. seas (B r o d ie , 1989;H a y & M a n s f ie l d , 1989). The genus Orcaella G r a y , 1866 was occasionally placed Keywords:beluga, narwhal, Monodontidae, Pliocene, North Sea, in the family Monodontidae but most recent studies palaeobiogeography. identify it as a Delphinidae (M uiZO N , 1988a;ARNOLD & H e in s o h n, 1996; LEDUC et al., 1999). Résumé Except for non-diagnostic material (e.g., N e w t o n , 1882), the only fossil Monodontidae described is Un squelette partiel découvert dans le Pliocène inférieur d’Anvers Denebola brachycephala B a r n e s , 1984 from the (nord de la Belgique), comprenant un crâne fragmentaire, latest Miocene of Mexico (B a r n e s , 1984). Following constitue la première mention d’un membre fossile de la famille Monodontidae en Mer du Nord. Le vertex du crâne est plus WHITMORE (1994), Delphinapterus sp. is a prominent bas que sur le plus ancien Monodontidae connu, Denebola member of the fauna of the Yorktown Formation, brachycephala, Miocène terminal, et l’orbite est positionnée plus Early Pliocene of the east coast of North America (one antérieurement. Ce crâne diffère des deux espèces actuelles de la undescribed skull and numerous ear bones). A periotic famille, le bélouga Delphinapterus leucas et le narval Monodon monoceros, par, entre autres, l’orbite plus courte et l’encoche of Delphinapterinae is cited by M uiZON & D eV r ie s antéorbitaire plus courte et plus large. La partie antérieure de la (1985) from the Early Pliocene of Sacaco, Peru. 198 Olivier LAMBERT & Pierre GIGASE PILLERI (1986) and P il l eri et al. (1989) referred several ear bones from the Miocene of South Southern North Sea Germany and Italy to Monodontidae. Later, BlANUCCI & L a n d in i (2002) and BlANUCCI (1996) relocated these specimens in other odontocete families. Kai lo A ntw erp The purpose of this paper is the description of new monodontid material (a fragmentary skull and some post-cranial fragments) from the early Pliocene of Antwerp, North of Belgium. Predation/scavenging marks are observed on the specimen and their origin is briefly commented. Additionally, several ear bones from the Neogene of the Antwerp area are described and similarly referred to a monodontid. The Fig. 1 — Map of the north of Belgium indicating the palaeobiogeography of the monodontids and other locality of Kallo, NW to Antwerp. Inset: map crown-delphinoids is finally discussed. of the southern part of the North Sea Basin (mod. from LOUW YE et al., 2004). Material and methods cysts from the Kattendijk Formation studied in two Specimens, see Appendix. sections of the Verrebroek Dock and Deurganck Institutional abbreviations. IRSNB, Institut royal des Dock, less than 2 km from the Vrasene Dock, give Sciences naturelles de Belgique, Brussels; M, Fossil an age between 5.0 Ma and 4.7-4.4 Ma, early Early mammal collection of types and figured specimens of the Pliocene (L o u w y e et al., 2004). Two isolated atlases, IRSNB; RMNH, Naturalis Nationaal Natuurhistorisch undoubtedly from the same species, were found in the Museum, Leiden, The Netherlands; ZMA, Zoölogisch same locality and level (Paul Gigase pers. comm.). Museum Amsterdam, The Netherlands. •.THE NETHERLANDS Systematic palaeontology Order Cetacea B r is s o n, 1762 BELGIUM Suborder Odontoceti F l o w e r, 1867 Superfamily Delphinoidea GRAY, 1821 Family Monodontidae GRAY, 1821 2 km Monodontidae indet. Doei Figs 3-8, Tables 1-2 Referred specimen. IRSNB M.1922, specimen including a partial skull, atlas and axis, vertebral Deurganck epiphyses and rib fragments. Dock Locality. Eastern wall of Vrasene Dock, Kallo, western bank of Schelde River, NWW of Antwerp (Figs. 1, 2). Geographic coordinates: 51o15’N-04o14’E. Kallo Vrasene Dock Horizon. Kattendijk Formation, about 6 m above the Verrebroek Dock City of Antwerp basis, Lower Pliocene (De M e u t e r & L a g a , 1976). The thin layer in which the specimen was found, rich Fig. 2 — Map of the Scheldt River and main docks of in large bivalves, is mentioned by HERMAN (1975) at the Antwerp Port giving the position of the the level -13.50 m, located 2-4 m under the Oorderen Vrasene Dock where the main specimen was Sands Member (Lillo Formation). Dinoflagellate found (mod. from LOUW YE et al., 2004). Early Pliocene monodontid _________199 width base rostrum e2x90 Description width right premaxilla at base rostrum 35 Skull width right maxilla at base rostrum 55 The preserved elements of this fragmentary skull, preorbital width of skull e2xl32 lacking the basicranium and nearly the whole rostrum, postorbital width of skull e2xl53 are: most of the right premaxilla, maxilla and frontal on the cranium, a smaller part of the left side, two maximum width of right premaxilla 65 fragments of mesethmoid, the right lacrimal and length of orbit (ventral tip preorbital-ventral tip 68 jugal, an isolated portion of the supraoccipital shield, postorbital) a fragment of the right squamosal and most of the right vertical length of right postorbital process of 42 alisphenoid sutured to fragments of parietal, squamosal frontal and basisphenoid. longitudinal distance anterior margin naris 109 The skull is somewhat smaller than adult - antorbital notch Delphinapterus leucas (see Table 1), probably similar horizontal length of temporal fossa el58 in size to the bottlenose dolphin Tursiops truncatus. Table 1 — Measurements (in mm) of the skull IRSNB Premaxilla. The premaxillary foramen is located 55 M. 1922, Monodontidae indet. from the Early mm posterior to the notch (Fig. 3); a similar posterior Pliocene of Antwerp, North Sea Basin, (e) position o f the foramen is observed in Delphinapterus indicates estimate. leucas, Denebola brachycephala and Monodon monoceros. Among other extant delphinoids, only some phocoenids and Orcaella possess a premaxillary maxilla su lcu s prem axilla dorsal infraorbital median exposition foram ina of maxilla prem axilla m esethm oid / postorbital p ro c e ss premaxillary foram en postero-lateral su lcu s shark teeth marks (grooves lacrimal and scales) antorbital notch dorsal infraorbital foramina postero-median sulcus antero-median sulcus Fig. 3 — Skull of IRSNB M. 1922, Monodontidae indet. from the Early Pliocene of Antwerp, North Sea Basin. A dorsal view. Note the shark teeth marks at the rostrum base. B schematic reconstruction of the preserved portion of the skull in dorsal view. Scale bar = 50 mm. 200 Olivier LAMBERT & Pierre GIGASE foramen somewhat posterior to the antorbital notch. monoceros. It immediately follows the depression and A median triangular depression, made by the joined gives the dorsal surface of the skull a more angulated depressed median parts of the two premaxillae, lateral profile than in D.