The third and youngest record of the species Megascyliorhinus trelewensis is described from the uppermost beds of the Paraná Formation outcropping in the Provincia de Entre Ríos, Argentina. Megascyliorhinus trelewensis is an endemic marine South American species of a rare and extinct genus. The species of Megascyliorhinus were widely distributed and appears to have been mainly restricted to warm temperate waters.El tercer y más joven registro de la especie Megascyliorhinus trelewensis se describe a partir de dientes hallados en las capas superiores de la Formación Paraná aflorantes en la Provincia de Entre Ríos, Argentina. Megascyliorhinus trelewensis es una especie endémica de Sudamérica de un género raro y extinto. Las especies de Megascyliorhinus se distribuyen ampliamente y parece haber estado restringidas a aguas templado cálidas.Fil: Cione, Alberto Luis. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - La Plata; Argentina. Universidad Nacional de La Plata. Facultad de Ciencias Naturales y Museo; ArgentinaFil: Mennucci, Jorge Augusto. Universidad Nacional de La Plata. Facultad de Ciencias Naturales y Museo; ArgentinaFil: Pérez, L.. Universidad Nacional de La Plata. Facultad de Ciencias Naturales y Museo. División Paleozoología Invertebrados; ArgentinaFil: Barla, María Julia. Universidad Nacional de La Plata. Facultad de Ciencias Naturales y Museo; Argentin

Barla, María Julia

Cione, Alberto Luis

Mennucci, Jorge Augusto

Pérez, L.

English

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Temas de la Biodiversidad del Litoral IIIF.G. Aceñolaza (Coordinador - Editor)INSUGEO, Miscelánea, 17: 41-48Tucumán 2008 - ISSN 1514-4836 - ISSN On-Line 1668-3242Megascyliorhinus trelewensis (Neoselachii) in the?Middle-Upper Miocene of Paraná, Central easternArgentinaAlberto Luis CIONE1, Jorge MENNUCCI1, Leandro PÉREZ2, and MaríaJulia BARLA3Abstract: Megascyliorhinus trelewensis (NEOSELACHII) IN THE ?MIDDLE-UPPER MIOCENE OF PARA-NA, CENTRAL EASTERN ARGENTINA.-The third and youngest record of the species Megascyliorhinustrelewensis is described from the uppermost beds of the Paraná Formation outcropping in the Provincia deEntre Ríos, Argentina. Megascyliorhinus trelewensis is an endemic marine South American species of a rareand extinct genus. The species of Megascyliorhinus were widely distributed and appears to have been mainlyrestricted to warm temperate waters.Key words: Elasmobranchii, South America, Argentina, Entre Ríos, Miocene.Resumen: Megascyliorhinus trelewensis (NEOSELACHII) EN EL MIOCENO MEDIO?-SUPERIOR DEPARANÁ, ARGENTINA ORIENTAL. El tercer y más joven registro de la especie Megascyliorhinus trele-wensis se describe a partir de dientes hallados en las capas superiores de la Formación Paraná aflorantes en laProvincia de Entre Ríos, Argentina. Megascyliorhinus trelewensis es una especie endémica de Sudamérica deun género raro y extinto. Las especies de Megascyliorhinus se distribuyen ampliamente y parece haber estadorestringidas a aguas templado cálidas.Palabras clave: Elasmobranchii, Sudamérica, Argentina, Entre Ríos, Mioceno.IntroductionThe extinct genus Megascyliorhinus was created by Cappetta and Ward (1977) forincluding the Miocene species Rhincodon miocenicus Antunes y Jonet, 1970 from Portugaland Morocco and the Eocene species M. cooperi from England. Posteriorly, the genus wasrecorded in other continents (see below).A new species, M. trelewensis, was described from early Miocene beds inPatagonia (Cione, 1986). Recently, one tooth of this species was found in sediments ofthe same age from central Chile (Suárez et al., 2006). In this note, we report the occurren-ce of M. trelewensis in the ?middle-late Miocene Paraná Formation of Argentina.GeologyThe continental and marine beds in the Paraná riverside cliffs in Entre Ríos,Argentina have been scientifically known since 1827 when Alcide D'Orbigny visited thearea (D'Orbigny, 1842; Figs. 1, 2). The relationships between the marine and continentalunits cropping out in the cliffs were studied by many researchers. Most authors identi-1. División Paleozoología Vertebrados, Museo de La Plata, 1900 La Plata, Argentinae-mail: acione@museo.fcnym.unlp.edu..ar2. División Paleozoología Invertebrados, Museo de La Plata, 1900 La Plata, Argentina3. Facultad de Ciencias Naturales y Museo, 122 y 60, 1900 La Plata, Argentina42 MISCELÁNEA 17fied only one marine unit recognizable (Paraná Formation) at the base of the cliffs andin subsoil (Ameghino, 1906; Scartascini, 1954; Aceñolaza, 1976; Herbst and Zabert,1987). The Paraná Formation is overlain by a thick fluvial (Ituzaingó Formation) and aterrestrial sequence. In subsoil, the Paraná Formation includes deposits of fluvial origin.Aceñolaza (1976) suggested that the marine beds located at higher levels in the riversidecliffs are relicts of an ancient topography that had been interpreted as different marineingressions, especially by Frenguelli (1920). The Paraná Formation is mainly composedby green mudstones, sands, limestones, and several oyster banks (Aceñolaza, 1976, 2000).The Paraná Formation was deposited during the large marine encroachment that cove-red the Chacopampean region during the middle Miocene and part of the late Miocene("Mid Transgressive Onlap Sequence;" see Uliana and Biddle, 1988; del Río, 1990, 1991;Cione et al., 2000, 2005). Mammals occurring in the base of the overlying ItuzaingóFormation are Huayquerian in age in the South American chronology (Cione, 2000;Cione and Tonni, 2005). The Huayquerian ranges from about 9 Ma to about 6 Ma(Tortonian, late Miocene; sea Flynn and Swisher, 1995; Cione et al., 2000, 2005; Cioneand Tonni, 2005; Woodburne et al., 2006).Section at La JuanitaThe material was collected from marine rocks belonging to the uppermostpart of the Paraná Formation exposed in a locality called La Juanita (GPS: 31°52´46”S60°38´59”W; Figure 1) (Pérez et al., 2001). This locality is close to the Aldea Brasileravillage in the Departmento de Diamante, Provincia de Entre Ríos. The section exposedmeasures seven meters (Figure 2). The lowermost bed includes alternating whitish toyellowish sands and green siltstones, both strongly bioturbated by Ophiomorpha nodosa.Figure 1: Location map. La Juanita, Arroyo Ensenada. The arrow point to the locality43MEGASCYGASCYLIORHINUS TRELEWENSISFigure 2: Stratigraphic section at La JuanitaThe rhythmic stratification is interrupted by an erosional bed of lenticular geometry,with a lateral extension of at least 150 meters along the cliff. It shows a normal grada-tion from beds with sabulitic matrix at the bottom to sandy matrix at the top, forming acoquina with bioclasts of different grain sizes. Towards the middle of the section thereis a strong carbonate cementation between the bioclasts and the siliceous ones. Themaximum thickness of this bed is about 50 cm. A rich vertebrate and invertebrate faunais present in the lens. The base of the section is covered by debris fallen from the cliffand the top by vegetation.44 MISCELÁNEA 17SystematicsElasmobranchiiNeoselachiiCarcharhiniformesCarcharhinidaeGenus Megascyliorhinus Cappetta and Ward, 1977Megascyliorhinus trelewensis Cione, 1986Figure 3Figure 3: Megascyliorhinus trelewensis. Anterior teeth. a-d. MLP 86-II-27-44 (Gaiman Formation, early Miocenefrom the lower río Chubut valley, Chubut, Argentina). e-h. CICYTTP-PV-P-1-126 (Paraná Formation, middle-early late Miocene from the La Juanita, Entre Ríos, Argentina). a, e: lateral view. b, f: lingual view. c, g: labialview. d, h: basal view. The bar is one mm.45MEGASCYGASCYLIORHINUS TRELEWENSISMaterialCICYTTP-PV-P-1-126, CICYTTP-PV-P-1-127, CICYTTP-PV-P-1-127,CICYTTP-PV-P-1-128, four anterior teeth. Paraná Formation fossiliferous bed at LaJuanita, Aldea Brasilera, Entre Ríos, Argentina. The material is deposited in the Centrode Investigaciones Científicas y Técnicas y Transferencia, Dr. Materi y España 3105Diamante, Entre Ríos, Argentina. Another tooth was found by ALC in the FlorentinoAmeghino Collection of the Museo Argentino de Ciencias Naturales “BernardinoRivadavia,” Angel Gallardo 470, Buenos Aires, Argentina. It was labeled “Squatina” byFlorentino Ameghino.DiagnosisMegascyliorhinus of large size; crown curving lingually; labial face very stronglyand deeply striated; lingual face with delicate, sinuous, anastomosing striations; lateralcutting edge sometimes reaching the base of the crown; lobes of the root divergingstrongly; base of the root not flat, but with lobes inclined toward anterior central line inthe lingual region. Basal root groove never reaching lingual face or absent. Lateral den-ticles differently developed. Lateroposterior teeth stocky (Cione, 1986).DescriptionTeeth present crown strongly curved lingually. The labial and lingual faces areconvex and there are almost paralell striations on the lower third of the both lingual andlabial faces. The cutting edges are not well preserved, and they extend a short distancebelow the crown apex. Striations on the lingual face extend one-third from crown base,they are fine, less deep, rather sinuous and more numerous and closer than those of thelabial face. On the labial face there are strong and shorter striations. The root-crownjunction is constricted. A sulcus, interrupted on the labial face separates the divergentroot lobes, which are of different size. The lingual region has a protuberance with a midvertical groove. The lingual protuberance bears two lateral foramina, mesolingual anddistolingual, and a central foramen on the vertical groove. The teeth have two straightand well developed lateral denticles, round in cross section, with a striated crown surfa-ce. The baso-apical section of the crown shows an orthodentine-type structure.CommentsAntunes y Jonet (1970) formerly attributed the species R. miocenicus to thewhale shark genus Rhiniodon (using the junior synonym Rinchodon; Orectolobiformes,Rhiniodontidae). Later, Cappetta and Ward (1977) created the genus Megascyliorhinus forthe species M. miocenicus and M. cooperi and assigned it to the family Carcharhinidae of theorder Carcharhiniformes. Some other authors consider it referable to FamilyParascyllidae of Order Orectolobiformes (e.g. Fitzgerald, 2004). We here refer the genusto Order Carcharhiniformes according to external characters and histology (see alsoAdnet, 2000).46 MISCELÁNEA 17Stratigraphic and geographic distribution of MegascyliorhinusThe extinct genus Megascyliorhinus has been found, always with relatively rarespecimens, from the Eocene (Ypressian) of England (Cappetta and Ward, 1977), theOligocene of Czech Republic ((Brzobohaty and Kalabis, 1970; Cappetta and Ward,1977) and Belgium (Baut and Génault, 1999), the Miocene (Helvettian and probablySerravallian) of France (Cappetta and Ward, 1977), United States (Purdy et al, 2001;Bourdon, 2007) and Japan (Hiroyuki and Karasawa. 1991), late Miocene-early Plioceneof Australia (Fitzgerald, 2004), the Pliocene of Tunisia (Cappetta and Ward, 1977), theTertiary of Chatham Rise (Pfeil, 1984), the Oligocene to Pleistocene of New Zealand(Keyes, 1984). The South American record is restricted to the species M. trelewensis inthe Lower Miocene of Patagonia and Chile so far. The occurrence of the SouthAmerican endemic species M. trelewensis in Paraná is the first record of the genus in youn-ger beds and the northernmost in the continent. No Pliocene record is known in SouthAmerica (e.g. in Peru, where there is an abundant elasmobranch record). The extremelyabundant Eocene record of Antarctica does not include Megascyliorhinus (Cione, 1978;Arratia and Cione, 1996). Besides, the Paraná Formation ichthyofauna does not appearto be tropical (Cione et al., 2000, 2005). Consequently, according to the present knowled-ge, the genus had a bipolar distribution and appears to have been restricted to warm tem-perate waters.PaleoecologyMegascyliorhinus species are marine taxa. However, the faunal assemblagefound at La Juanita includes organisms from diverse environments. Paleoecologicalanalysis of the bioclastic bed received special attention, as it includes both marine andfreshwater organisms, but also includes terrestrial tetrapods.Among the marine fossils found there are large numbers of shell belongingto molluscs that inhabited nearshore environments. This is the case of pectinids, arcoids,mytiloids and veneroids. There are also marine fish such as sharks and ray, together withmarine turtles and cetaceans. Also abundant are brackish water molluscs such as mac-trids oysters and Erodona, among others. Among the fishes, there are some amphibioticor continental taxa such as drums, and doradid and ariid catfishes. Less abundantly, someterrestrial vertebrates occur. They are represented by few bird bones, xenarthran plates,and rodent teeth. These fossils may have been added to the sediment during the stormevent that probably originated the shelled deposit.This fossil assemblage clearly shows an environmental averaging, which pro-duced the mixed array of taxa recorded at this locality. However, it is clear that theassemblages from different environments were coetaneous, because the remains showlittle evidence of transport as it is shown by the fine ornamentation details preserved inthe mollusc shells and the intact edges of the smaller valves.47MEGASCYGASCYLIORHINUS TRELEWENSISAcknowledgmentsWe would like to thank to Carlos Steger, for loaning part of the material, and the Agencia Nacional dePromoción Científica y Tecnológica, Consejo Nacional de Investigaciones Científicas y Técnicas, Comisión deInvestigaciones Científicas de la Provincia de Buenos Aires, Universidad Nacional de La Plata, andInternacional Association of Sedimentology for permanent financial support.BibliographyAceñolaza, F.G. 1976. 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Mesozoic-Cenozoic paleogeographic and gedynamic evolution of sou-thern South America. Revista Brasileira de Geociências 18:172-190.Woodburne, M. O., A. L. Cione, and E. P. Tonni. 2006. Central American Provincialism and the Great AmericanBiotic Interchange. In: Carranza-Castañeda, O. & E.H. Lindsay (eds.) Advances in late Tertiary ver-tebrate paleontology in Mexico and the Great American Biotic Interchange. Publicación Especial delInstituto de Geología y Centro de Geociencias de la Universidad Nacional Autónoma de México 4:73-101.Recibido 20 de noviembre de 2007Aceptado 15 de diciembre de 2007

Megascyliorhinus trelewensis (Neoselachii) en el mioceno medio-superior de Paraná, Argentina oriental

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Megascyliorhinus trelewensis (Neoselachii) en el mioceno medio-superior de Paraná, Argentina oriental

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