Rivista Italiana di Paleontologia e Stratigrafia volume tuj numero 2 pagíne 259-262 Settembre 1997 A NE\T FIND OF HEA/TISYNTRACHELUS (CETACEA, DELPHINIDAE) FROM PIACENZIAN SEDIMENTS OF RIO STRAMONTE (NORTHERN APENNINES, ITALY) GIOVANNI BIANUCCI Key-uords: Cetacea, Delphinidae, Systematics, PIiocene, Northern Apennines, Italy. Riassunto. Viene descritto un cranio incompleto di Hemisyn- tachelus sp. (Cetacea, Delphinidae) scoperto nelle marne argillose ptacenziane di Rio Stramonte (provincia di Piacenza). Questo nuovo ritrovamento conferma l'alta frequenza, nel Pliocene, di Hemisyntra- chel u s nell' are a periadriatica. Abstract. An incomplete skull of Hemisynnachelus sp. (Ceta- cea, Delphinidae) is described from the Piacenzian clayey marls of Rio Stramonte (Piacenza, Italy). The new find confirms the abundan- ce of Henisyntrachelus in the peri-Adr)atrc area during the Pliocene. Introduction. In the spring of 1.991. Mr. Migliorini discovered a fossil delphinid skull preserved in Pliocene clayey maris that crop out near Rio Stramonte, a small stream in the northern Apennines Qracenza, Italy) (Fig. 1). The speci- men was collected by the Gruppo Paleontologico "La Xenophora" of Castell'Arquato (a village near the disco- very locality) and following restoration, is now kept in the Geological Museum of Castell'Arquato. The Pliocene sequence of Rio Stramonte has been referred to the Piacenzian (Monegatti Ec Ranieri, 1e87). The holotype of Hernisyntracbelus cortesii (Fischer, 1,829) and another almost complete skeleton of this spe- cies were found in the same locality in the past (Cortesi, 1819; Cuvier, 1823; Del Prato, 1.897; Cígala Fulgosi, 1990). More generally, several significant cetacean fossils, including two almost complete skeietons of balenopte- rid, have been discovered in the northern Apennines of Pracenza province, in the same facies known in the lite- rature as "argille azzvrre"(see Francou, 1985). Another probable balenopterid was recently excavated (1986) in this area by the Gruppo Paleontologico "La Xenopho- ra". This specimen, retrieved from Lower Pliocene sedi- ments of Monte Oliveto, also is preserved in the Geolo- gical Museum of Castell'Arquato. Systematic description Class Mammalia Linnaeus, 1758 Order Cetacea Brisson, L762 Suborder Odontoceti FIower, 1762 Family D e I p h i n i d a e Gray, 7825 Genus Hemisyntrachelws @randt, 1873) Type-species: H. cortesii (Fischea 1829) Hemisyntrachelus sp. (Fis.2-3) The specimen consists of an incomplete skull (ac- king the rostrum, part of the left side of the neurocra- nium, the right antorbital process and the hamular pro- cesses of the pterygoid$. The auditory bones, the man- dible, the teeth and all of the postcranial skeleton are not preserved. The skull size is larger than that of contemporary Tursiops, but more closely resembling that of Hemisyn- tracbelus, a genus recently re-described and referred to the family Deiphinidae (Bianucci, 1996, 1997). The wide exposirion of the frontals, in dorsal vieq suggests an immature animal, like the specimen described by Sacco (1893). The left dorsal portion of the braincase is iost and an endocranial cast is exposed. In lateral view, the temporal fossa is relatively large and is antero-poste- riorly elongated as in Tursiops and Hemisyntrachelws, while differing from the round-shaped fossa of the con- Dipanimento di Scienze della Terra, via S. Maria, 53,56126 Pisa (Italy) 260 G. Bianucci Fig. 1 - Geographic location of Hemisyntracbelzs sp. described. temporaneous genus Astadelphis Bianucci, 7996. The or- bit is placed relatively anteriorly, as in Hemiryntrachelus, and the zygomatìc process of the squamosal is antero- posteriorly elongated. Among the living genera, this process more closely resembles that of Pseudorca than the short process of Tursiops. The skull size, the shape of the temporal fossa, the advancement of the orbit and the elongation of the zygomatic process of the squamosal indicate that the specimen belongs to the genus Hemisyntracbelus. A specific attribution is not possible since the ro- strum and the mandible, defining characters of the two species H. cortesii and H. pisanus are lacking in this specimen. Vidth of rostrum at base Vidth of premaxillae at base of rostrum Greatest oostorbital width 180 106 320 Tab. 1 - Heznislntachelzs sp. Estimated measurements (in mm). Discussion. The discovery of a new specimen of. Hemisyntra- chelus confirms the reiative abundance of this fossil ge- nus in the Pliocene of the Peri-Adriatic area. In fact, !1. of 16 significant delphinid records are referred to this genus (Bianucci, 1996, 1997). Partícularly in the Emiiia Piacenzian Delphinidae Hemisyntrachelzs sp. Rio Stramonte (northern Apennines, Italy), Fr, frontal; Mx, maxilla; N, nasal; Occ, occipital; Pmx, premaxilla 261 Piacenzian. lncomplete skull in dorsal view. Ec, endocranial cast; Scale : 5 cm. Fio 2 F;o 1 Hemisyntracbehr sp. Rio Stramonte (nonhern Fr, frontal; Mx, maxilh; Occ, occipitalr Pop, squamosal.Scale:5cm. Apennines, Italy), Piacenzian. Neurocranium of the incomplete skull in lateral view. postorbital process; Sq, squamosal; Tf, temporal fossa; Zp, zigomatic process of the area (provinces of Piacenza, Parma, and Bologna) all well-preserved delphinid records (Z specimens) belong to Hemisyntrachelus. The abundance of this genus might be related to its feeding habits (Hemisyntrachelus was probably a gene- ralist and opportunistic predator) and the restricted width of the Peri-Adriatic basin. This last condition might not have favoured the diffusion of open sea del- phinids such as Stenella, that instead inhabited the pa- leo-Thyrrenian sea. AchnouLedgements. I thank Dr. P Miculan for information concerning the new cetacean finds and for his assistance during my visit to the Geological Museum of Castell'Arquato. I also wish to thank the director of this museum, Dr. C. Francou, for granting me access to the fossil cetacean collection. I am grateful to Prof. V. Landini (Dipartimento di Scienze della Terra, University of Pisa) for useful discussions and suggestions. I am also indebted to Dr. D. J. Bohaska (\Washington) for critically reading the manuscripr. The illustrations are by the author and the photos by Mr. M. Gini (Dipanimento di Scienze della Terra, University of Pisa) and the author. 262 G. Biznucci REFERENCES Bianucci G. (1996) - The Odontoceti (Mammalia, Cetacea) Del Prato A. (1897) - Il Thrsiops Capellinii Sacco del Pliocene from Italian Pliocene. 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