Klaas Post 1 & Mark Bosselaers 2 1 Natuurhistorisch Museum Rotterdam 2 Berchem, Antwerpen Late Pliocene occurrence of Hemisyntrachelus (Odontoceti, Delphinidae) in the southern North Sea

Post, K. & Bosselaers, M., 2005 - Late Pliocene occurrence of Hemisyntrachelus (Odontoceti, Delphinidae) in the southern North Sea - DEINSEA 11: 29-45 [ISSN 0923-9308]. Published 29 December 2005

Late Pliocene Hemisyntrachelus is reported from the southern North Sea, marking the youngest and northernmost occurrence of the genus. The mandibular morphology of the North Sea fossils is compared to Pliocene Hemisyntrachelus from Italy, the status and characteristics of the genus are discussed and arguments for the inclusion of Early Pliocene Tursiops oligodon from Peru in this genus are presented.

Keywords: Late Pliocene, Hemisyntrachelus, Tursiops oligodon, Odontoceti, Delphinidae, North Sea

Correspondence: K. Post, Natural History Museum Rotterdam, P.O. Box 23452, 3001 KL Rotterdam, the Netherlands, e-mail [email protected]; M. Bosselaers, Lode van Berckenlaan 90, 2600 Berchem, Antwerpen, Belgium, e-mail [email protected]

INTRODUCTION ribs and thoracic vertebrae and the morphology The fossil dolphin genus Hemisyntrachelus of the lumbar vertebrae being different from Brandt, 1873 is based on material from the those in Tursiops. Although Slijper was fol- Pliocene of Italy, with Delphinus cortesii lowed by some authors (e.g. Simpson 1945), Fischer, 1829 designated as the type spe- others continued to disagree (e.g. Pilleri 1979) cies. It was placed in the Delphinapteridae or expressed reservations and the need for fur- by Brandt (1873) without further explanation ther study (Barnes et al. 1985, Barnes 1990). or systematic arguments. Previous to Brandt, Bianucci (1996) presented reasons to maintain Cuvier (1823) had already noted that some Hemisyntrachelus at the genus-level, such as fossil Tursiops-like crania from Italy showed a rostrum that is broader at the base, a more characters ‘intermediate’ between Tursiops and robust antorbital process, a smaller number of Orcinus. larger teeth, a shorter tooth row and a pecu- The close resemblance of Hemisyntrachelus liar mandibular symphysis in comparison to and Tursiops caused controversy about the Tursiops. He included Hemisyntrachelus in the validity of the genus and the two have often Delphinidae on the basis of two apomorphies: been considered synonymous (cf. Capellini a wide mesethmoid in dorsal view and the 1882, Portis 1885). Nevertheless, Slijper reduction of the posterior ascendant branch of (1936) resurrected Hemisyntrachelus and the premaxilla. Slijper (1936) and Bianucci coined the family Hemisyntrachelidae for it. (1996) thought Hemisyntrachelus and Tursiops Slijper’s decision was based on morphological to be contemporaneous because they consid- considerations, in particular the articulation of ered Tursiops ossenae Simonelli, 1911 from

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the Pliocene of Italy to be a ‘genuine’ Tursiops. genus. The North Sea fossils are compared In an attempt to a phylogenetic analysis, with Italian Hemisyntrachelus specimens, Bianucci (1996) compared Hemisyntrachelus as well as with some Recent Delphinidae, to with Tursiops, while at the same time making reconsider the validity of the genus and to remarks on features perceived ‘intermedi- establish distinctive characters for it. We also ate’ between Hemisyntrachelus, Tursiops, summarize the Late Pliocene marine mam- Orcinus and Pseudorca. He presented three mal fauna of the southern North Sea of which hypotheses on the phylogenetic relation- Hemisyntrachelus was a member. ships of Hemisyntrachelus, of which the one considered most parsimonious by MATERIAL AND METHODS him shows Hemisyntrachelus as the sister All important fossils of Hemisyntrachelus in taxon of Pseudorca, Orcinus, and ‘other Italian collections were studied during the Globicephalinae’. However, a recent study summer of 2003. Extant delphinids in the col- based on full cytochrome b sequences (LeDuc lections of KBIN, NNM and ZMA were used et al. 1999) showed that Tursiops is para- for comparison. For measurement methodol- phyletic, with Tursiops aduncus sharing a more ogy, see Fig. 1. Special attention was given to recent common ancestor with Delphinus and the following specimens: some species of Stenella than with Tursiops Hemisyntrachelus cortesii, cast of holotype truncatus. Moreover, LeDuc et al. (1999) (MP); found the Delphininae to be not closely related Hemisyntrachelus pisanus, holotype (MB to Orcinus and Pseudorca, with Orcinus being 1coc14); outside the Globicephaline clade to which Tursiops oligodon, holotype (SMNK pal. Pseudorca belongs. Clearly, further investiga- 3841); tions are needed in order to resolve the phylo- Tursiops ossenae, holotype (MB 8561); genetic position of Hemisyntrachelus. Orcinus citoniensis, holotype (MB 1coc11); Apart from Delphinus cortesii, other nomi- Tursiops capellinii (= Hemisyntrachelus nal taxa that have at times been included cortesii) (MPP 48-48); in Hemisyntrachelus are Tursiops brochii Hemisyntrachelus sp. (NMR 9991-01756, Capellini, 1863; Tursiops capellinii Del NMR 9991-01757, Y-1409, A-3231). Prato, 1897; Tursiops astensis Sacco, 1891; Tursiops cortesii var. pedemontana Sacco, Collection acronyms 1891 and Hemisyntrachelus pisanus Bianucci, A - private collection of mr L. Anthonis of 1996, but - in his review of the genus - only Bouwel, Belgium cortesii and pisanus were considered valid by IFG - Museo di Geologia e Paleontologia Bianucci (1996), who relegated brochii, capel- dell’Università di Firenze, Florence, Italy linii, astensis and pedemontana to the syn- KBIN - Koninklijk Belgisch Instituut voor onymy of cortesii. Natuurwetenschappen, Brussels, Belgium Pilleri (1979) speculated that taxa tradition- MB - Museo Giovanni Cappellini ally included in Hemisyntrachelus originated dell’Università di Bologna, Italy from an exclusively Italian radiation, but this MP - Museo di Storia Naturale e del Territorio view finds little support in the dubious taxo- Certosa di Calci dell’Università di Pisa, nomic status of some of the nominal taxa and Calci, Italy the controversial nature of the genus itself. MPP - Museo di Paleontologia dell’Università Here, we present data on recently discovered di Parma, Italy specimens, assigned to Hemisyntrachelus, NMR - Natuurhistorisch Museum Rotterdam, from the latest Pliocene of the southern North the Netherlands Sea, thereby considerably extending the known NNM - Nationaal Natuurhistorisch Museum geographical and stratigraphical range of the Naturalis, Leiden, the Netherlands

30 POST & BOSSELAERS: Hemisyntrachelus in the North Sea

Figure 1 Measurements taken on delphinid mandibula in this study.

NWHCH - Norfolk Museums and Archaeology antorbital process of the frontal, periotic with Service, Norwich, UK robust anterior process and low pars coch- SMNK - Staatliches Museum für Naturkunde, learis with wide external auditory window, Karlsruhe, Germany broad tympanic - in ventral view - with a nar- Y - private collection of mr C. van Hooydonk row medial lobe, short dental rows with 14-16 of Rucphen, the Netherlands robust teeth and short mandibular symphysis. ZMA - Zoölogisch Museum, Universiteit van Moreover Bianucci (1997) considers the robust Amsterdam, the Netherlands anterior process of the periotic as distinctive for the genus. Most of the postcranial and cra- CHARACTERISTICS OF nial characters cannot be recognized unambig- HEMISYNTRACHELUS uously in fragmented fossils, but mandibular Slijper (1936) stated that Hemisyntrachelus characters in Hemisyntrachelus are remarkably differs from other delphinid genera (such as constant and easy to quantify, as well as well- Tursiops and Orcinus) by the shape of the lum- differentiated from other delphinid genera (Fig. bar vertebrae and the articulation of the ribs. In 2), to the extent that even fragments of man- his emended diagnosis of the genus Bianucci dibulae can be identified unambiguously. (1996, 1997) compared Hemisyntrachelus to Tursiops and listed the following distinc- The mandibula of Hemisyntrachelus differs tive characters: sturdy vertebrae, atlas with a from all other Delphinidae by the combination dorso-ventrally compressed neural arch and of the following characters (see Table 1): pointed transverse processes, broad base of a - low length/height ratio of the symphysis long rostrum, not narrowing premaxilla on the (< 1.6); apical portion of the rostrum, deep and narrow - presence of a prominent ventral keel on the antorbital notch, square-shaped neurocranium symphysis; in dorsal view, anterior location of the robust - few labial foramina mentis (< 4);

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Figure 2 Mandibular characters of Hemisyntrachelus (bottom) compared with those of other delphinid genera.

32 POST & BOSSELAERS: Hemisyntrachelus in the North Sea

- downward sloping mandibular tip; - size of teeth (Ø of alveolae > 12 mm); - less than 17 teeth per tooth row; - estimated tooth count of 12. - teeth robust, round and pointed (Ø of alveolae > 8 mm) Unfortunately, so far no complete mandibula has been found in the southern North Sea, The Hemisyntrachelus specimens from the but based on the diameter of the teeth versus southern North Sea show all the diagnostic the length of the ramus it is likely that the characters of the genus and can be distin- North Sea Hemisyntrachelus had 12 (certainly guished from the known species of the genus < 14) teeth in the dental row. This assump- by the following characters (see Table 1): tion is perhaps corroborated by a single left - extremely short symphysis (length/height maxilla [NWHCH 15.76(2)] from the Late ratio < 1.3); Pliocene Norwich Crag of Britain illustrated - a single large mental foramen within the by Newton (1891: 79), which shows 12 alveo- symphyseal border; les. However, based on a maxillary fragment, - symphyseal border posterior to the third Hemisyntrachelus (and many other delphinids) alveolus; cannot be identified unambiguously.

Table 1 Mandibular characters of several Delphinid taxa compared with Hemisyntrachelus specimens from Italy (IFG 1547) and the southern North Sea.

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Figure 3 Mandible fragment IFG 1547, an Italian specimen matching the characters of Hemisyntrachelus from the southern North Sea.

34 POST & BOSSELAERS: Hemisyntrachelus in the North Sea

A study of mandibular characters of Italian and not very prominent mandibular symphy- specimens revealed two distinct groupings sis in the shape characteristic for the genus. within the two Hemisyntrachelus species (see Five deep cylindrical alveoles for robust teeth Table 1): are seen on the dorsal side of the mandibula, - the typical cortesii group. The majority of the ramus being broken at the sixth alveole. Italian specimens are characterized by a rela- A large, deep and funnel-shaped foramen is tively long symphysis (length/height ratio present on the lateral side of the ramus at about > 1.3, < 1.6), two or - less often - more 18 mm below the position of the fourth alveole mental foramina, and 14-16 relatively and about 61 mm from the anterior edge of the slender teeth (alveolar Ø 10-14 mm). Both mandibula. The ventral edge of the symphysis the holotypes of cortesii and pisanus fall forms a prominent keel. within this grouping. - a single specimen (IFG 1547; Fig. 3), which NMR 9991-01756 (Fig. 6) - A well-preserved matches the characters of Hemisyntrachelus distal part of a left mandibula, collected during from the southern North Sea (see below), April 2000 by mr L. Anthonis. On the medial with a symphyseal length/height ratio < 1.3, side, the 92 mm long ramus shows a short large, robust and almost round alveoli with and not very prominent mandibular symphy- a mean alveolar diameter of 15 mm, and a sis, characteristic for Hemisyntrachelus. Five single, large and pronounced mental deep, cylindrical alveoles for robust teeth are foramen. present on the dorsal side of the mandibula, the ramus being broken just after the fifth alveole. DESCRIPTION OF NORTH SEA A large, deep and funnel-shaped foramen is MATERIAL present on the lateral side of the ramus, about All specimens were collected from stockpiles of 19 mm below the position of the fourth alveole a shell reworking factory at Yerseke, province and 61 mm posterior to the anterior edge of of Zeeland, the Netherlands. the mandibula. Two very small foramina are present on the mandibular edge, with the ven- Y-1409 (Fig. 4) - A well-preserved distal part tral part of this edge forming a prominent keel. of a left mandibula, collected in 2000 by mr. C. van Hooydonk of Rucphen, the Netherlands and NMR 9991-01757 (Fig. 7) - A well-preserved stored in his private collection. On the medial distal part of a right mandibula, collected in side, the 138 mm long ramus shows a short and 2000 by mr T. Lambrechts. On the medial side, weak mandibular symphysis, characteristic for the 114 mm long ramus shows a short and not the genus. Seven deep and cylindrical alveoles, very prominent mandibular symphysis, charac- that clearly held robust teeth, are situated on the teristic for the genus. Seven deep, cylindrical dorsal side of the mandibula, the ramus being alveoles are located on the dorsal side of the broken at the eighth alveole. A single large, mandibula, the ramus being broken at the posi- deep and funnel-shaped foramen is positioned tion of the eighth alveole. A large, deep and on the lateral side at about 14 mm below the funnel-shaped foramen is present on the lateral fourth alveole and about 58 mm posterior to the side of the ramus about 22 mm below the posi- anterior edge of the mandibula; the lower part tion of the fourth alveole and about 66 mm of this edge forms a sharp and prominent keel. posterior to the anterior edge of the mandibula. The ventral part of this edge is eroded, but A-3231 (Fig. 5) - A well-preserved distal part shows signs of a prominent keel having been of a left mandibula, collected during November present. 2000 by mr L. Anthonis, Bouwel, Belgium and stored in his private collection. On the medial side, the 114 mm long ramus shows a short

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Figure 4 Y-1409, a well-preserved distal part of a left mandibula of Hemisyntrachelus from the southern North Sea.

36 POST & BOSSELAERS: Hemisyntrachelus in the North Sea

Figure 5 A-3231, a well-preserved distal part of a left mandibula of Hemisyntrachelus from the southern North Sea.

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Figure 6 NMR 9991-01756, a well-preserved distal part of a left mandibula of Hemisyntrachelus from the southern North Sea.

38 POST & BOSSELAERS: Hemisyntrachelus in the North Sea

Figure 7 NMR 9991-01757, a well-preserved distal part of a right mandibula of Hemisyntrachelus from the southern North Sea.

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STRATIGRAPHY whereas the ‘Westkapelle Ground Formation’ The shells stockpiled at the shell rework- consists of early Tiglian marine sediments. ing factory at Yerseke are dredged from the Here, the typical marine mammal fauna is Roompot area, at the outlet of the former always found together with fossils from a well- Oosterschelde estuary (Fig. 8). At this loca- documented Tiglian TC3 land fauna typified by tion, the Early Pleistocene ‘IJmuiden Ground Anancus arvernensis, Mammuthus meridiona- Formation’ and the Late Pliocene ‘Westkapelle lis, Stephanorhinus etruscus and Eucladoceros Ground Formation’ are sub-cropping at or ctenoides (de Vos et al., 1998). The marine just below the sea floor (Ebbing et al., 1992). mammal fauna probably originates from the The somewhat older Late Pliocene ‘Brielle ‘Westkapelle Ground Formation’, while it is Formation’ is located well below the sea floor likely that the warmer land mammal fauna and, therefore, a surface mixture of older comes from the ‘IJmuiden Ground Formation’. Pliocene elements can be safely excluded. Therefore, we conclude that Hemisyntrachelus Marine mammal fossils from the Roompot area fossils from this locality have to be dated as are of a dull black colour and are completely Late Pliocene (2-1.8 Ma, not younger than mineralised. Tiglian TC3), allowing for the possibility - and, The ‘IJmuiden Ground Formation’ is a pro- indeed, the probability - that at least parts of delta sediment of Tiglian to Eburorian age, the marine mammal fauna may also be present

Figure 8 Coastal configuration and components of the North Sea delta during Praetiglian - Early Tiglian, c. 2.4 Ma (after Funnell 1996). A Roompot; B Noordhinder; C Outer Gabbard; D Easton Bavents.

40 POSTPOST &et BOSSELAERS:al.: mute swan Hemisyntrachelusbiometrics in the North Sea

in older Pliocene sediments. However, there are hypothesis is difficult to prove because none of reasons to restrict Hemisyntrachelus to the latest these fossils is collected in situ and therefore Pliocene, as unambiguous Hemisyntrachelus we limit ourselves to the study of the mandibu- fossils have neither been found in earlier lae only. At both locations, the ‘Westkapelle Late Pliocene sediments, such as the Belgian Ground Formation’ (or its lateral component, ‘Kruisschans Sands’ and ‘Merksem Sands’, nor the ‘Smits Knoll Formation’) sub-crops at the in the well-studied Early and Middle Pliocene sea bottom, but the slightly older ‘Red Crag sediments of Belgium. Formation’ and ‘Brielle Formation’ are also Large numbers of postcranial fossils of present near the sea floor (Cameron et al., Hemisyntrachelus and the contemporary 1984). marine mammal fauna have been collected in The marine mammal fauna typically associ- other parts of the North Sea (e.g. Noordhinder, ated with Hemisyntrachelus is also found in 52º30’N-02º40’E, and Outer Gabbard, 52º10’N situ at Easton Bavents along the British east - 02º10’E; Fig. 8) and are stored in Naturalis coast (Fig. 8). Although the stratigraphy of and in several private collections in The this site has been a source of debate since Netherlands. These postcrania are morpho- the 19th century, recent finds of the Pliocene logically similar to the Italian postcrania and walrus Alachtherium and other marine mam- it seems beyond reasonable doubt to link the mals at this locality are unambiguously of postcrania and the mandibulae to one and the latest Pliocene age (Funnell & West 1962, same genus. A problematic fact is that this A.J. Stuart & N. Larkin in litt.). It appears that

Table 2 The Late Pliocene marine mammal association of the southern North Sea.

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during the Late Pliocene, a peculiar marine Pliocene Hemisyntrachelus in Peru demon- mammal fauna occurred in the North Sea, with strates that the genus is neither endemic to the Hemisyntrachelus probably being present dur- Mediterranean (cf. Pilleri 1987, Bianucci 1997) ing a limited time frame only. nor restricted to the Mediterranean and the North Atlantic, but had a much wider distribu- MARINE MAMMAL ASSOCIATION tion and a temporal occurrence spanning at Fossil material of a multitude of marine least the Early to Late Pliocene, implying that mammals, listed in Table 2, have been col- future finds of Hemisyntrachelus elsewhere in lected from the Late Pliocene of the North the Pacific are to be expected. Sea locations Roompot, Noordhinder, Outer Till date, two species of Hemisyntrachelus Gabbard and Easton Bavents. Except for (H. cortesii and H. pisanus) have been Hemisyntrachelus and Alachtherium, this described, both from Italy. H. pisanus dif- largely unstudied faunal association consists fers from H. cortesii by its larger dimensions, of extant genera. At the species level, at least aspects of the periotic, and especially in the Physeter sp., Orcinus sp., Globicephala sp., straight ventral line of the mandibula compared Delphinapterus sp., and probably two phocids, to the more inclined shape of the mandibula in appear to represent as yet undescribed taxa. H. cortesii (Bianucci 1996). In our study, we were unable to identify significant mandibular DISCUSSION differences between the two species (cf. Table Several cranial and hundreds of post-cranial 1). Scrutinizing the mandibles of the holotype fossils confirm the Late Pliocene presence of of H. pisanus revealed that the jaws were care- Hemisyntrachelus in the southern North Sea. fully but extensively restored. We are of the This delphinid was a member of a temperate to opinion that the typical shape of the ventral cold marine mammal fauna, mainly consisting border of the mandibula might have been of extant genera. Some of the members of this caused by restoration. Since delphinid periotics fauna were already present in the area during do not allow for unambiguous identification the Middle and Late Pliocene (e.g. Eubalaena, at the species level (Bianucci 1996), we must Delphinapterus, Alachtherium), while consider the possibility that H. pisanus is a others, such as Hemisyntrachelus, may have large sized H. cortesii and that the differences been restricted to the latest Pliocene. In Italy, in size are the result of sexual dimorphism, a Hemisyntrachelus occurred throughout the hypothesis corroborated by recent finds of very entire Pliocene (Bianucci 1996, 1997, in litt.). large specimens of H. cortesii (Bianucci 1997). Pilleri & Siber (1989) described Tursiops The fact that one specimen (IFG 1547), oligodon from the Early Pliocene Pisco amongst a multitude of Italian Hemisyn- Formation of Peru and remarked on trachelus fossils, shows characteristics simi- its resemblance to Italian Tursiops (= lar to those of the North Sea fossils seems Hemisyntrachelus) cortesii. Based on the mas- striking, but this may just as well prove that sive structure of the cranium, the long and our knowledge of the Late Pliocene marine broad rostrum, the anterior location of the mammal fauna of Europe is only limited. This orbit, the deep antorbital notch, the morphol- is illustrated by Orcinus citoniensis, an orca ogy of bulla and periotic, and particularly the from the same Italian fauna that produced characters of the mandibula (downward slop- Hemisyntrachelus, which - despite 120 years ing tip, short symphysis with a length/height of paleontological exploration - is known from ratio of 1.5, pronounced keel on the ventral a single skeleton only. part of the symphysis, and the 12 almost Bianucci (1997) made a remark on globi- round, robust teeth), we conclude that Tursiops cephaline features in Hemisyntrachelus, such oligodon shows all of the characteristics of as the broad rostrum, the small medial lobe on Hemisyntrachelus. The presence of Early the bulla, and the margin of the premaxilla.

1442 POST &et BOSSELAERS:al.: mute swan Hemisyntrachelusbiometrics in the North Sea

Although phylogenetic conclusions are beyond tions can be made. Hemisyntrachelus is a the scope of the present paper, we might point delphinid that can be distinguished from out that Bianucci’s observation is corrobo- Tursiops, Globicephala and Orcinus and other rated by the lack of variation in mandibular Delphinidae by its mandibular characteristics. characters among the nominal taxa included It was present in the Mediterranean during in Hemisyntrachelus at present, which is in the Pliocene, in the northeastern Atlantic dur- marked contrast to most delphinids, and by the ing the Late Pliocene and in the southeastern characteristically downward sloping tip of the Pacific during the Early Pliocene and was part mandibula of Hemisyntrachelus. of a temperate to cold marine mammal fauna. In conclusion, the following observa- Based on the present study, H. pisanus from

Figure 9 MPP 48-48 Hemisyntrachelus cortesii of the Pliocene of Italy; SMNK-PAL. 3841 Hemisyntrachelus oligodon of the Early Pliocene of Peru; and (bottom) Y-1409, a mandible fragment possibly of an as yet unnamed species from the Pliocene of Italy and the Late Pliocene of the southern North Sea.

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Italy should be considered conspecific with ACKNOWLEDGEMENTS H. cortesii, while Tursiops oligodon from Dr G. Biannuci and dr M. Bisconti (both from Peru should be included in Hemisyntrachelus. the Università di Pisa, Italy) as well as dr O. This study also indicates that the fossils from Lambert and dr G. Lenglit (KBIN Brussels, the southern North Sea and a single Italian Belgium) were helpful in many ways. Mr C. specimen might represent a new species. van Hooydonk and mr L. Athonis allowed However, because of the fragmentary nature of access to their private collections. We also the material it seems prudent to refrain from thank the curators of the fossil mammalcol- formally naming a new species until more lections at Parma, Florence, Bologna, Pisa, complete fossils become available. Therefore, London and Norfolk, who allowed access Hemisyntrachelus presently includes two and to the collections under their care and pro- perhaps three species, viz. Hemisyntrachelus vided working conditions. Prof. A.J. Stuart cortesii (Fischer, 1829) of the Pliocene of (University College, London, UK) and dr N. Italy, Hemisyntrachelus oligodon (Pilleri & Larkin (Norwich Castle Museum, UK) pro- Siber, 1989) of the Early Pliocene of Peru, and vided us with information on the stratigraphy possibly an as yet unnamed species from the of Easton Bavents, and dr C. Laban and dr K. Pliocene of Italy and the Late Pliocene of the Rijsdijk (TNO-NITG, Utrecht, Netherlands) southern North Sea (Fig. 9). were helpful in unravelling the geological secrets of the North Sea bottom. Last but not least we have to thank dr C.J. Hazevoet (Lisboa, Portugal) for making several usefull suggestions and comments during the prepara- tion of this paper.

REFERENCES Capellini, G., 1882 - Del Tursiops cortesii e del delfino Barnes, L.G., 1990 - The fossil record and evolutionary fossile di Mombercelli nell’Astigiano - Mem. R. Acc. relationships of the genus Tursiops. In: S. Sci. Ist. Bologna 3: 569-578 Leatherwood & R.R. Reeves (eds) - The bottlenose de Vos, J., D. Mol & J.W.F. Reumer, 1998 - Early dolphin, pp. 3-25. Academic Press, San Diego Pleistocene mammalian remains from the Barnes, L.G., D.P. Domning & C.E. Ray - 1985. Status Oosterschelde or Eastern Scheldt (province of of studies on fossil marine mammals - Marine Zeeland, the Netherlands) - Med. Ned. Inst. Mammal Science 1: 15-53 Toegepaste Wetenschappen TNO 60: 173-188 Bianucci, G., 1996 - The Odontoceti (Mammalia, Ebbing, J.H.J., C. Laban, P.J. Frantsen & H.P. Nederlof, Cetacea) from Italian Pliocene. Systematics and phy- 1992 - Geological Survey of the Netherlands. logenesis of Delphinidae - Palaeontographia Italica Rabsbank sheet, Dutch licence blocks for oil and 83: 73-167 gas. S7, S8, S10 and S11 (51º20’N–03º00’E) - Rijks Bianucci, G., 1997 - Hemisyntrachelus cortesii (Cetacea, Geologische Dienst Delphinidae) from the Pliocene sediments of Campore Funnell, B.M., 1996 - Plio-Pleistocene Palaeogeograpphy Quarry (Salsomaggiore Terme, Italy) - Bulletino della of the southern North Sea Basis (3.75-0.60 Ma) - Società Paleontologica Italiana 36: 75-83 Quaternary Science Reviews 15: 391-405 Brandt, J.F., 1873 - Untersuchungen über die fossilen und Funnell, B.M. & R.G. West, 1962 - The Early Pleistocene subfossilen Cetacean Europas - Mém. Acad. Imp. Sci. of Easton Bavents, Suffolk - Quarterly Journal of the St.-Pétersbourg (Sér. 7) 20: 1-372 Geological Society of London. 118: 125-141 Cameron, T.D.J., C. Laban & R.T.E. Schüttenhelm, LeDuc, R.G., W.F. Perrin & A.E. Dizon, 1999 1984 - Geological Survey of the Netherlands, Flemish - Phylogenetic relationships among the delphinid Bight, sheet 52ºN-02ºE, Quaternary Geology - British Cetaceans based on full cytochrome b sequences - Geological Survey Marine Mammal Science 15: 619-648

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Newton, E.T., 1891 - The Vertebrata of the Pliocene (Cetacea, Odontoceti) aus der Pisco-Formation Perus deposits of Britain - Memoirs of the Geological - Beiträge zur Paläontologie der Cetaceen Perus, pp. Survey of the United Kingdom, London 1-137 165-192 Pilleri, G., 1979 - Taxonomic status of “Cortesi’s dol- Portis, A., 1885 - Catalogo descrittovo dei Talassoterii phin” (Tursiops cortesii Keferstein, 1834) from the rinvenuti nei terreni terziari del Piemonte e della Lower Pliocene of N. Italy - Investigations on Liguria - Mem. R. Acc. Sci. Torino 37: 247-365 Cetacea 10: 71-83 Simpson, G.G., 1945 - The principles of classification Pilleri, G., 1987 - The Cetacea of the Italian Pliocene and a classification of mammals - Bull. Amer. Mus. with a descriptive catalogue of the species in the Nat. Hist. 85: i-xvi, 1-350 Florence Museum of Paleontology - Brain Anatomy Slijper, E.J., 1936 - Die Cetaceen. Vergleichend-anato- Institute, Ostermundingen misch und systematisch - Capita Zool. 7: i-xv, 1-590 Pilleri, G. & H.J. Siber, 1989 - Neuer Delphinid

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