An Oplegnathid beak (Osteichthyes: Perciformes) from the Early Miocene of Patagonia. Extirpation of several vertebrates from the southern Atlantic Ocean Un Oplegnathidé (Osteichthyes : Perciformes) du Miocène inférieur de Patagonie. Extirpation de plusieurs vertébrés de l’Atlantique du sud Alberto Luis Cione * Departamento científico, paleontología vertebrados zoología, facultad de ciencias naturales y Museo, Museo de La Plata, universidad nacional de La Plata, 1900 La Plata, Argentina Received 18 October 2000; accepted 12 November 2001 Abstract The first record of the knifejaw family Oplegnathidae in the Atlantic Ocean and in South America is reported. It comes from the lowermost beds of the Early Miocene Gaiman Formation at the lower Río Chubut valley, central-eastern Patagonia. The family Oplegnathidae does not occur in the Atlantic today, but it was widespread in comparison to other knifejaw fishes, such as scarids and odacids. Several aquatic vertebrates were extirpated from the southern Atlantic Ocean in the Late Neogene. This record establishes a minimal age (Early Miocene) for the extirpation of the family Oplegnathidae in the Atlantic Ocean. © 2002 Éditions scientifiques et médicales Elsevier SAS. All rights reserved. Résumé La présence de la famille Oplegnathidae dans l’Atlantique et en Amérique du Sud est signalée pour la première fois dans les niveaux les plus inférieurs de la Formation Gaiman d’âge Miocène inférieur, dans la vallée du Rio Chubut, partie centrale de la Patagonie est. Les Oplegnathidés sont inconnus dans l’Atlantique de nos jours mais cette famille était largement distribuée en comparaison avec les scaridés et les odacidés. Plusieurs vertébrés aquatiques furent extirpés de l’Atlantique sud au cours du Néogène tardif. Cette découverte fixe un âge minimal (Miocène inférieur) pour la disparition de la famille Oplegnathidae de l’Océan Atlantique. © 2002 E´ditions scientifiques et médicales Elsevier SAS. Tous droits réservés. Keywords:Miocene; Patagonia; Perciformes; Oplegnathidae; Extirpation; Atlantic Ocean Mots clés:Miocène; Patagonie; Perciformes; Oplegnathidae; Extirpation; Océan Atlantique 1. Introduction Fossil perciform knifejaw fishes are rare (Oplegnathidae, Scaridae) or unknown (Odacidae). Most of the supposed fossil records of the perciform family Scaridae are currently assigned to Oplegnathidae(Bellwood and Schultz, 1991). The oldest known oplegnathid comes from the Eocene of Antarctica (Cione et al., 1994). Knifejaw fishes of the family Oplegnathidae are widespread in warm-temperate and warm seas today(Cione et al., 1994). In this paper, several oplegnathid premaxillary bones from Miocene rocks in southern Argentina are described and the extirpation of several marine taxa in the southern Atlantic Ocean is briefly discussed. * Corresponding author. E-mail address:acione@museo.fcnym.unlp.edu.ar (A.L. Cione). Geobios 35 (2002) 367–373 www.elsevier.com/locate/geobio © 2002 Éditions scientifiques et médicales Elsevier SAS. All rights reserved. PII: S 0 0 1 6 - 6 9 9 5 ( 0 2 ) 0 0 0 3 2 - 3 2. Recent and fossil comparative material 2.1. Recent material Oplegnathidae: Oplegnathus insignis (Museo Nacional de Historia Natural, Santiago, Chile). Odacidae: Neoodax balteatus MLP 9086, Olisthops cyanomelas MLP 9085. Scaridae, Scarus sordidus MLP 9087 (Museo de La Plata, La Plata). Additional unregistered material of the Tetra- odontidae, Diodontidae, Scaridae, and Odacidae was also examined. 2.2. Fossil material Oplegnathidae indet., Eocene, Seymour Island, Antarc- tica, MLP 93-1-6-5, left premaxilla; MLP 90-1-20-141, jaw fragment; MLP 91-11-4208, jaw fragment. 3. Stratigraphic setting The material comes from the lowermost beds of the Gaiman Formation at the localities Bryn Gwyn (White Hill in Welsh) and the informal “Campo de Pristiophorus” . The Gaiman Formation crops out in the middle part of the southern cliffs in the lower Río Chubut valley. Bryn Gwyn is 4 km south of the city of Gaiman (43°15' S–065°30' W; Chubut province, Argentina, Fig. 1; Cione, 1986, 1988). The Late Eocene to Early Miocene marine rocks of eastern Patagonia are referred to the Julian and Leonian stages (see Ameghino, 1900–1903, 1906). The Gaiman Formation is correlated with the Late Leonian Stage (Ameghino, 1900–1903; Bertels, 1970; Cione, 1988). Ca- macho (1974) introduced a partially different stratigraphic pattern for the marine Tertiary of Patagonia, based on some index fossils and lithology. Camacho removed from the Julian and Leonian stages, the rocks he named “Estratos con Neoinoceramus” and “Estratos con Monophoraster y Vene- ricor” . Both units were assigned to the Eocene (Camacho, 1974; Legarreta et al., 1990). The base of the Gaiman Formation was referred to the “Estratos con Monophoraster y Venericor” (CAMACHO, 1974). However, the “Estratos con Neoinoceramus” and “Estratos con Monophoraster y Venericor” are correlated with the Leonian Stage (Cione, 1986, 1988; Cione and Expósito, 1980; Cione and Cozzuol, 1990; Barreda, 1989). Correlation of the type Monte León Formation and Gaiman Formation is based on stratigraphic relationships, ash and biogenetic silica content, and fossil evidence (Cione, 1978, 1986, 1988; Cione and Expósito, 1980; Cione and Cozzuol, in preparation; Riggi, 1979). Although fora- minifera are unknown from surface outcrops of the Gaiman Formation, the typical Julian–Leonian “Asociación de Cri- brorotalia” has been found in rocks of this unit in a well-log in eastern Chubut (Masiuk et al., 1976). The Gaiman Formation conformably overlies the Trelew Member of the continental Sarmiento Formation which includes Colhuehuapian fauna (Cione, 1988). No radioiso- topic dates from rocks with Colhuehuapian fauna are available (Flynn and Swisher, 1995). The Deseadan Stage underlies the Colhuehuapian Stage. The Deseadan is cur- rently known to span from about 24.5 to 29 Ma (Late Oligocene; Flynn and Swisher, 1995). From beds at the base of the Gaiman Formation at Bryn Gwyn, 40K-40Ar dates have been reported (Bown et al., 1988; Bown and Larriestra, 1990; 15.8 ± 2.5 and 16.6 ± 0.8 Ma). These ages are close to the Burdigalian and Langhian boundary. However, verte- brate evidence suggests that at least the base of the unit is Aquitanian in age. The marine Middle Miocene Puerto Madryn Formation overlies the Gaiman Formation in the area. The marine flooding seems to have been at its maximum when the Gaiman, Pinturas, and part of Monte León and Centinela Formations were deposited. These formations could correlate with the sequence set of the beginning of the Aquitanian (TB1-1.4) or with the sequence of the upper part of the Aquitanian and the Burdigalian (TB2-2.1) of Haq et al. (1987). According to Harland et al. (1990), the first sequence set ranges from about 23.3 Ma. 4. Systematic paleontology Family: OPLEGNATHIDAE Bleeker, 1855 Genus: Oplegnathus Richardson, 1840 Oplegnathus sp., Fig. 2 Material: MPEF-PV-548, an eroded fragment of a pre- maxilla. MLP 77-XII-22-417, a fragmentary right premax- illa. MLP 86-II-27-2, a fragmentary right premaxilla. Low- Fig. 1. Sketch map showing the Río Chubut lower valley. (1) Bryn Gwyn. (2) “Campo de Pristiophorus” . Fig. 1. Carte montrant la vallée inférieure du Rio Chubut. (1) Bryn Gwyn. (2) “Campo de Pristiophorus” . 368 A.L. Cione / Geobios 35 (2002) 367–373 ermost beds of the Gaiman Formation at the southern cliffs of the río Chubut valley, facing the city of Gaiman, Departamento de Gaiman, Provincia del Chubut, Argentina. The repositories are the Departamento Científico Paleon- tología Vertebrados, Facultad de Ciencias Naturales y Mu- seo, Universidad Nacional de La Plata, La Plata, Argentina (MLP), and the Museo Paleontológico “Egidio Ferugli” , Trelew, Argentina (MPEF-PV). Description: individual teeth are exposed in the outer surface of dental plates forming tooth rows which are scarcely imbricated (Fig. 2(2)). In MLP 77-XII-22-417, the surface is partially covered by “cement” (see Bellwood, 1995) as those described from the Eocene of Antarctica (Cione et al., 1994). Each row has at least five or six teeth (Figs. 2(2), 4 and 5). Each tooth has a distal surface covered by enameloid with weak ornamentation. Such surface is a flattened half-moon with an apical sharp cutting edge. Teeth in MLP 86-II-27-2 are more acuminated than those of MLP 77-XII-22-417 and those described from the Eocene of Antarctica (Cione et al., 1994; Figs. 2(2) and 5). Teeth near symphysis are larger than lateral ones. Eleven large molari- form teeth occur in the lingual occlusal area of MLP 77-XII-22-417 (see also MPEF-PV-548; Figs. 2(2) and 3). These teeth are similar to those of the material of Antarctica (MLP 90-I-20-141; Cione et al., 1994). The molariform teeth are larger than those of the outer dental plate surface. Two rather conical teeth occur near the symphysis in MLP 77-XII-22-417 (Fig. 2(1)). The symphysis is broad and smooth with four teeth in a row in the labial margin (MLP 77-XII-22-417 and MPEF-PV-548; Fig. 2(2)). Fig. 2. Oplegnathidae indet. Gaiman Formation, Early Miocene, Chubut Province. (1,2) MLP 77-XII-21-417, Bryn Gwyn, occlusal and labial view of a left premaxilla, ×4. (3,4) MPEF-PV-548, Bryn Gwyn, occlusal view of a left premaxilla, ×3.5. (5) MLP 86-II-17-2, “Campo de Pristiophorus” , labial view of a right premaxilla, ×7. Fig. 2. Oplegnathidae indet., Miocène inférieur, Province de Chubut. (1,2) MLP 77-XII-21-417, Bryn Gwyn, vues occlusale et labiale du prémaxillaire gauche, ×4. (3,4) MPEF-PV-548, Bryn Gwyn, vue occlusale du prémaxillaire gauche, ×3.5. (5) MLP 86-II-17-2, “Campo de Pristiophorus” , vue labiale du prémaxillaire droit, ×7. A.L. Cione / Geobios 35 (2002) 367–373 369 5. Discussion Large rounded molariform teeth on the medial face of the jaws differentiate the Patagonian material from knifejaw beaks of other families, such as Tetraodontidae, Diodon- tidae, Odacidae, and Paleolabridae (see Estes, 1969; Britski et al., 1985; Gomon and Paxton, 1985). Diodontidae and Tetraodontidae show teeth completely covered by an enam- eloid layer without individual teeth erupting on the cutting edge. In the family Odacidae, there are usually small, conical, and tightly imbricated teeth (Gomon and Paxton, 1985). Coalesced teeth also occur in another two families, namely, Scaridae and Oplegnathidae. Both families show molariform teeth on the lingual area of the occlusal face of the jaws (Bellwood and Schultz, 1991; Bellwood, 1995). Nonetheless, the absence of lateral canines, present in all but a few scarid species, and the form of the teeth with a distinct bipartite structure differentiate the material from scarids. Additionally, the shape of the teeth distinguishes the Patagonian material from the scarid genera Calotomus, Leptoscarus, Hipposcarus, Cryptotomus, Nicholsina, Scarus, and some Sparisoma. Due to the presence of a crenate cutting edge and the lack in some of lateral canines, the material resembles the scarid genera Bolbometopon, Cetoscarus, Chlorurus, and some Sparisoma, although only species of the latter shares the presence of molariform teeth on the medial face of the jaws with the Patagonian material. In addition, the medial molariform teeth of some Sparisoma are smaller than those of the Patagonian maxilla and lateral canines are present in most Sparisoma species. A bony ridge running inside the anterior teeth of those scarids without fused dental teeth is absent in oplegnathids and in the Patagonian material. In summary, the morphology of the Patagonian material agrees with that present in the monogeneric Family Opleg- nathidae. Dental autapomorphies of oplegnathids are un- known at present (Bellwood, 1995; Cione et al., 1994). Yet, in members of that family, the jaws have a distinctly crenate cutting margin and loose lateral canines; the teeth show a narrow cutting edge and may evidence a bipartite structure. Also, large rounded molariform teeth occur on the medial face of the jaws. For these reasons, the material is consid- ered provisionally assignable to Oplegnathus. 6. Associated fishes Many fishes (mostly sharks) have been collected in the lowest 5 m of the Gaiman Formation near Gaiman (Ameghino, 1900–1903, 1906, 1935; Cione, 1978, 1986, 1988; Cione and Pandolfi, 1984; Arratia and Cione, 1996; Cione and Cozzuol, in preparation). Fish taxa recorded are mainly elasmobranchs: Hexanchus griseus, Heterodontus sp., Pristiophorus sp., Squatina sp., “ Isurus” hastalis, Isurus retroflexus, Carcharoides totuserratus, Odontaspis sp., Car- charocles productus, Galeorhinus sp., Myliobatis sp. A few teleosts were also reported: Molidae indet., Labrodon sp., and Perciformes indet. 7. Biogeographic and paleoclimatic remarks This is the first record of an oplegnathid in South America and in the southern Atlantic Ocean. Recent species of Oplegnathus are patchily distributed in relatively deep waters in warm-temperate seas in western Australia, Tasma- nia, Japan, Hawaii, northern Chile, Galapagos and Easter islands, and the east coast of South Africa (Fig. 3; de Buen, 1959; Bellwood and Schultz, 1991; Cione et al., 1994). Fossil records show that the family was more widely distributed during the Cenozoic than at present day. Fossil oplegnathids occur in the Eocene of Antarctica, Oligocene of Europe, and Miocene of Australia and western North America (Chapman and Cudmore, 1924; Bellwood and Schultz, 1991; Cione et al., 1994). The family was extir- pated from Antarctica after the Middle Eocene and from the Atlantic Ocean after the Early Miocene. A similar extirpation (or remarkable reduction in distri- bution area) from the Atlantic Ocean is known for the shark families Heterodontidae, Pristiophoridae and the carchar- hinid genus Hemipristis, and the mammalian families Dug- ongidae and Monachinae. Specimens assignable to the genus Pristiophorus occur in the Paleocene of Morocco; Oligocene of Belgium and Holland; Miocene of Germany, France and Portugal; the Pliocene of France (Cappetta, 1987); the Oligocene and Miocene of Patagonia (Cione, 1988; Cione and Expósito, 1980), and the Eocene of Seymour Island, Antarctica (Grande and Eastman, 1986). An endemic species, Pristio- phorus schroederi persists in Cuba, Florida, and the Baha- mas (Compagno, 1984). The other species of Pristiophorus are distributed in the western Pacific off Japan, the Koreas, China, the Philippines, Australia, and possibly, in the Arabian Sea (Compagno, 1984). Specimens assignable to the genus Heterodontus occur in the Jurassic of Germany; Cretaceous of England, France, Lithuania, Belgium, and Texas; Paleocene of Denmark, England, Belgium, and Morocco; Eocene of Georgia, USA, England, Belgium, and Morocco (Cappetta, 1987); in Oli- gocene and Miocene rocks of Patagonia and eastern Argen- tina (Ameghino, 1906; Cione, 1978; Cione and Pandolfi, 1984). In the Atlantic Ocean, the youngest record of Heterodontus is Late Miocene in age (Ituzaingó Formation, eastern Argentina; Cione and Pandolfi, 1984; Cione, 1988) and the youngest record of Pristiophorus is Pliocene (Bel- gium; Cappetta, 1987). The species of Heterodontus pres- ently inhabit the Pacific and western Indian oceans (Compagno, 1984). Hemipristis was widely distributed in warm and temper- ate seas all over the world especially in the Miocene. It 370 A.L. Cione / Geobios 35 (2002) 367–373 occurs in the Eocene of Egypt, USA, Guinea Bissau, and Peru; in the Miocene of eastern USA, Argentina, Germany, France, Belgium, Italy, Cabinda and Zaïre, Java, India, Japan, and Australia; in the Pliocene of Angola, Zanzibar; and the Pleistocene of Celebes (Cappetta, 1987; Cione, 1988). The recent species Hemipristis elongatus occur in Australia, southern Asia, Red Sea, East Africa, Madagascar and in the western coast of Africa to 27° S (Compagno, 1984). Other aquatic vertebrates inhabited the southern Atlantic and also became extirpated from it after the Late Miocene. Dugongs of the genus Metaxytherium were recorded in the Early Miocene Pirabas Formation (Brazil; Paula Couto, 1979) and the Middle Miocene Paraná Formation (Argen- tina; Reinhart, 1976). Another dugong (Dioplotherium) occurs in the Pirabas Formation (Cozzuol, 1993). Dugongs of the family Dugongidae are presently distributed in the Red Sea, Indian Ocean, and western Pacific today (Paula- Couto, 1979). Hydrodamalin dugongs inhabited the north- ern Pacific until recently, but were killed by man. Monachin phocids occur in the Middle Miocene Puerto Madryn and Paraná formations and the Late Miocene Ituzaingó Formation of Argentina and Pliocene units of South Africa (de Muizón and Bond, 1982; Barnes et al., 1985; Cozzuol, 1993). Monachin seals are presently re- stricted to the Mediterranean and eastern North Atlantic, Caribbean and Hawaii (Cozzuol, 1993). The extirpation of high latitude biota was directly related with global and local coolings (Cione, 1988; Cione and Reguero, 1994; Kaiho, 1994). However, the extirpation of some sharks and teleosts (and some aquatic mammals) from the Atlantic Ocean is not explained by temperature changes because those fishes persisted in environments with similar temperatures in the Pacific and Indian Oceans. Sharks of the genus Heterodontus are small, sluggish bottom feeders that inhabit shallow, warm-temperate waters Fig. 3. Distribution of the family Oplegnathidae. The arrow indicates Trelew-Gaiman area. Isotherms of 15 and 20 °C for February (Southern Hemisphere) and August (Northern Hemisphere) are depicted (according to Sverdrup et al., 1942). Squares represent fossil records and circles indicate recent reports (Cione et al., 1994). Fig. 3. Distribution des Oplegnathidae. La flèche indique la zone Trelew-Gaiman. Les lignes isothermes 15 et 20 °C pour février (hémisphère sud) et août (hémisphère nord) sont représentées (d’après Sverdrup et al., 1942). Carrés = fossiles; cercles = actuels (Cione et al., 1994). A.L. Cione / Geobios 35 (2002) 367–373 371 occasionally straggling into the tropics (Springer and Gold, 1989). Pristiophorids are bottom dwellers with a limited distribution in temperate and tropical waters of continental and insular shelves (Springer and Gold, 1989). In the Atlantic Ocean, they are known only from deep water (640–915 m). Outside the Atlantic, sawsharks may occur in depths as shallow as 37 m and as great as 430 m (Springer and Gold, 1989). Oplegnathid fishes inhabit the fringe of the tropics and seem to be mostly limited by the summer isotherm of surficial waters of about 20 °C (Cione et al., 1994). The Patagonian material was found along with a temper- ate fish assemblage (see above). Recent fishes of the genera occurring in the Gaiman Formation inhabit marine waters located to the north of the latitude of Gaiman today, in the Argentinean Biogeographic Province, of warm-temperate waters (López, 1964; Cione, 1978; Menni, 1981). Most of the Patagonian shelf mostly corresponds to the Magallanian Biogeographic Province, of cold-temperate waters (López, 1964). Pristiophorus, Heterodontus, Hemipristis, and the oplegnathid remains occur in the same beds in the Gaiman Formation. Pristiophorus, Heterodontus, and oplegnathids involve bottom dwellers. We have not found a cause for the pseudoextinction of oplegnathids and heterodontids, and the great reduction of pristiophorids and Hemipristis in the Atlantic, however. Geologic events during the Late Ceno- zoic provoked extended environmental perturbations. These events included the restriction of the Mediterranean, the separation of the Pacific and Atlantic oceans by the rise of the Panama Isthmus, and strong fluctuations in sea level related with global climatic cooling. Shelf areas became greatly reduced during the Pleistocene glacial episodes. Yet, these or similar events also influenced most oceanic basins. Acknowledgements The authors thank the following institutions and persons: Mario Cozzuol (Porto Velho) for part of the material, the Consejo Nacional de Investigaciones Cientificas y Técnicas (CONICET), Agencia Nacional de Promoción Científica y Tecnológica and Facultad de Ciencias Naturales y Museo of the Universidad Nacional de La Plata for the permanent support; J. Paxton (Australian Museum), J. Lima de Figueiredo (Museu de Zoologia de Sâo Paulo), and Roberto Meléndez Cortés (Museo Nacional de Historia Natural, Santiago de Chile) for comparative material and literature. References Ameghino, F., 1900–1903. L’âge des Formations sédimentaires de Patago- nie. Anales de la Sociedad Científica Argentina 50, 109–130, 145–165, 209–229; 51, 20–39, 65–91; 52, 189–197, 244–250; 54, 161–180, 220–249, 283–342. Ameghino, F., 1906. Les formations sédimentaires du Crétacé supérieur et du Tertiaire de Patagonie avec un parallèle entre leurs faunes mammalogiques et celles de l’Ancien Continent. 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Extirpation of several vertebrates from the southern Atlantic Ocean Introduction Recent and fossil comparative material Recent material Fossil material Stratigraphic setting Systematic paleontology Discussion Associated fishes Biogeographic and paleoclimatic remarks Acknowledgmements References