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A New Genus of Dipnoiformes from the Cretaceous of Brazil

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A New Genus of Dipnoiformes from the Cretaceous of Brazil “main” — 2011/10/18 — 12:41 — page 1181 — #1 Anais da Academia Brasileira de Ciências (2011) 83(4): 1181-1192 (Annals of the Brazilian Academy of Sciences) Printed version ISSN 0001-3765 / Online version ISSN 1678-2690 www.scielo.br/aabc A new genus of Dipnoiformes from the Cretaceous of Brazil CARLOS E.V. TOLEDO1, ELIANE P. DE SOUSA2, MANUEL A.A. MEDEIROS3 and REINALDO J. BERTINI4 1USP/IGC/GSA, Rua do Lago, 562, Cidade Universitária, Butantã, 05508-080 São Paulo, SP, Brasil 2UEMA/CECEN, Cidade Universitária Paulo VI, Bairro Tirirical, Caixa Postal 09, 65000-000 São Luís, MA, Brasil 3Departamento de Biologia, Universidade Federal do Maranhão, Campus do Bacanga, Avenida dos Portugueses, s/n, 65085-580 São Luís, MA, Brasil 4UNESP/IGCE/DGA/NEPV, Avenida 24-A, 1515, Campus Rio Claro, Bairro Bela Vista, 13506-900 Rio Claro, SP, Brasil Manuscript received on November 13, 2009; accepted for publication on March 1, 2011 ABSTRACT The Alcântara Formation, an important stratigraphic unit from the early Cenomanian of Brazil, was deposited under transitional (estuarine) conditions, and its fossil record includes fragmentary remains of plants, fishes, crocodylomorphs, pterosaurs and dinosaurs, with a noteworthy diversity of dipnoiformes tooth plates. The dipnoiformes material reported here comprises a new taxon, Equinoxiodus alcantarensis, gen. et sp. nov. Most of the identified morphotypes of continental vertebrates collected in the Alcântara Formation are similar to chronocorrelative faunas from Northern Africa, but this new genus of Dipnoiformes indicates some degree of paleogeographic isolation and endemism. This was probably caused by the widening of the equatorial Atlantic Ocean during the early Cenomanian, which may have selectively affected some species. Key words: Dipnoiformes, neoceratodontids, Equinoxiodus alcantarensis gen. et sp. nov., Cretaceous. INTRODUCTION sensu other authors), which led them to conclude that the two basins are in fact one, now so-called São Luís- In 1994, a multiple layered bone-bed within iron-oxide Grajaú Basin (Fig. 1). cemented conglomeratic layers, alternating with sand- The bone-bed (Fig. 2), named Laje do Coringa stone levels, was discovered on the eastern side of (Corrêa-Martins 1997), is a sequence within the Alcân- the Cajual Island (2◦28053, 400S and 44◦27041, 300W) in tara Formation (Itapecuru Group) located on the eastern northern Maranhão State, northeastern Brazil (Corrêa- beach of the Cajual Island. It is unique in Brazil because Martins 1997). Measuring about four hectares in area, it crops out in a very restricted area exposed only dur- the bone-bed is exposed on a muddy beach, at low tide ing the low tide that has yielded thousands of bones, teeth twice a day. The tidal range exceeds six meters causing and petrified plants as conifers and ferns. During the past the beach to be frequently swept by waves that expose 16 years, an impressive number of specimens has been and free up the fossils from the rock matrix. Tradition- collected and studied, revealing a noteworthy continen- ally deposits in this region were considered as belonging tal palaeobiota that includes fishes, crocodylomorphs, to the São Luís Basin. However, a stratigraphic revision pterosaurs and dinosaurs. There is a remarkable num- undertaken by Góes and Rossetti (2001) demonstrated ber and diversity of dipnoiformes tooth plates, as well as instead its continuity southward with sedimentary se- some marine fishes and reptiles (Medeiros and Schultz quences of the Grajaú Basin ( northern Parnaíba Basin = 2001, 2002, 2004, Vilas Bôas and Carvalho 2001, Cas- tro et al. 2004, Medeiros et al. 2007, Elias et al. 2007, Correspondence to: Manuel Alfredo Araujo Medeiros E-mail: [email protected] Pereira and Medeiros 2008, Kellner et al. 2009). The An Acad Bras Cienc (2011) 83 (4) “main” — 2011/10/18 — 12:41 — page 1182 — #2 1182 CARLOS E.V. TOLEDO et al. Fig. 1 – Map of Northern Maranhão state showing main geological landmarks of the São Luís – Gajaú Basin, and the localization of the Alcântara Municipality (adapted from Rossetti 2003). fossilization was mostly by permineralization of bones, than one inch to about 15 cm, intercalated by stratified teeth and tooth plates by iron oxides. This permineral- sandstones. Holz (2003) considered the conglomerates ization took place concomitantly with the lithification of as lags assembling continental fossil material reworked the conglomerate, which was the result of iron oxides de- and re-deposited in marine sediments during a transgres- position (mainly goethite). Trunks of conifers and ferns sive episode. were distinctly fossilized by a combination of silica and Regarding lungfishes, a noteworthy diversity of iron oxides and probably have a more complex tapho- tooth plates has been collected and, thus far, some nomic history. have been identified: Ceratodus africanus (or Ceratodus The Itapecuru Group extends over the northern braziliensis sensu Cunha and Ferreira 1980), Asiatoce- Maranhão State, covering an extensive area inland and ratodus tiguidiensis, and Ceratodus humei (Medeiros along the shore. Albian and early Cenomanian deposits and Schultz 2001, 2002, Castro et al. 2004, Toledo et al. are well represented in this sedimentary sequence (Pe- 2005). The present work deals with the morphological drão et al. 1993a, b, c). Numerous continental fossils description and taxonomy of some tooth plates recov- have been recovered yielding much information about ered from the Laje do Coringa, which are considered to the northern South American environments, climate and represent a new genus and species of lung fishes. faunas, while the western Gondwana was breaking apart. GEOLOGICAL SETTING Laje do Coringa is thus far the richest fossiliferous site of the Itapecuru Group. It is formed by a few conglom- The richness of fossil deposits from the northern part of eratic lenses, each one varying in thickness from less São Luis-Grajaú Basin is a consequence of the rapid sub- An Acad Bras Cienc (2011) 83 (4) “main” — 2011/10/18 — 12:41 — page 1183 — #3 A NEW GENUS OF DIPNOIFORMES FROM BRAZIL 1183 Fig. 2 – Localization of the Laje do Coringa fossiliferous site (black dot), and a photo showing the bone bed during low tide. sidence of this region, which is situated on the Brazilian ENVIRONMENT AND CLIMATE equatorial margin. The region was directly affected by The palynological evidence for an arid tropical climate rifting, which created a tectonic depression that was filled throughout the early Albian to early Cenomanian is pro- out by sediments of the Itapecuru Group. This group lies vided by Pedrão et al. (1993a, b, c) and Rossetti and above Aptian strata of the Codó Formation. The Creta- Toledo (1996), who studied sedimentary features in out- ceous sedimentary sequence of São Luís-Grajaú Basin crops of the Alcântara Formation. This interpretation records the South American-African breakup (Aranha et is reinforced by the study performed by Amiot et al. al. 1990, Góes and Feijó 1994, Góes and Rossetti 2001, (2010) on Cretaceous material from Brazil and North Rossetti 2001). The upper sequences are divided into Africa, which also evidences higher surface tempera- two transitional units: the Alcântara and Cujupe for- tures than present-day arid to semi-arid environments mations. The Alcântara Formation contains sequences under tropical and equatorial climates. However, the that have been interpreted as an incised valley fill, which record of conifer woods and giant ferns suggests the were deposited under a tide-dominated palaeoenviron- presence of forests, and fishes such as Mawsonia and ment (Rossetti and Truckenbrodt 1997). This unit exten- Lepidotes give evidence of a substantial body of wa- sively outcrops in the coastal cliffs in São Marcos Bay, ter in this region. Mawsonia could grow to a length of in the Alcântara City region (Fig. 2). more than 3.5 meters, as evidenced by isolated bones from Laje do Coringa (to be published). Lepidotes would also require a considerable body of water to survive DATING judging by the size of the scales found in the deposits. The palynological analysis of sediments in the coast of On the other hand, the dinosaurian fauna, which in- the São Luis Island indicates the early Cenomanian age cludes very large animals like the titanosaurs and in the outcropping Cretaceous sediments (Pedrão et al. rebbachisaurids, had to be supported by rich vegetation 1993c). Klein and Ferreira (1979) also attributed a Ceno- nearby. Rich vegetation would obviously require a rela- manian age to these deposits, based on bivalves from an tive high degree of humidity. In order to reconcile both estuarine facies. In fact, subsidence was more intense aridity and humidity indicators in the same sedimentary along the shore line in the early Cenomanian, resulting sequence, the environment was interpreted as a conifer in faster and more massive accumulation of sediments in forest that would have been confined to the vicinity of that region compared with deposition rates further inland fluvial canals and surrounded by an arid to semi-arid (see revision in Rossetti et al. 2001). landscape (Medeiros and Schultz 2002). An Acad Bras Cienc (2011) 83 (4) “main” — 2011/10/18 — 12:41 — page 1184 — #4 1184 CARLOS E.V. TOLEDO et al. ASSOCIATED PALEOFAUNA the Mesozoic, mainly in the Cretaceous. Dipnoiformes Although very fragmentary, fossils of Laje do Coringa are represented by morphotypes referred to Cerato- are remarkably numerous. Teeth of some pterosaurs dontidae, Neoceratodontidae, Asiatoceratodontidae and and dinosaurs can be found in their hundreds, while fish Lepidosirenidae (Pascual and Bondesio 1976, Cunha and material like teeth and scales are counted in thousands. Ferreira 1980, Gayet and Brito 1989, Schultze 1991, Dinosaurian vertebral centra are also a common item. Bertini et al. 1993, Silva and Azevedo 1996, Dutra Among sauropods, titanosaurids and a rebbachisaurid and Malabarba 2001, Medeiros and Schultz 2001, 2002, are present (Medeiros and Schultz 2002, 2004, Medei- Castro et al. 2004, Toledo et al. 2005, Apesteguía et al. ros et al.
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