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New Species of Pygocephalomorpha (Crustacea) from the Irati Formation, Paraná Basin, Rs, Southern Brazil

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New Species of Pygocephalomorpha (Crustacea) from the Irati Formation, Paraná Basin, Rs, Southern Brazil Rev. bras. paleontol. 19(3):389-400, Setembro/Dezembro 2016 © 2016 by the Sociedade Brasileira de Paleontologia doi: 10.4072/rbp.2016.3.04 NEW SPECIES OF PYGOCEPHALOMORPHA (CRUSTACEA) FROM THE IRATI FORMATION, PARANÁ BASIN, RS, SOUTHERN BRAZIL KAREN ADAMI-RODRIGUES, PAULA GIOVANA PAZINATO Núcleo de Estudos em Paleontologia e Estratigrafia, UFPel, Praça Domingos Rodrigues, 02, 96010-440, Pelotas, RS, Brazil. [email protected], [email protected] †IRAJÁ DAMIANI PINTO Departamento de Paleontologia e Estratigrafia, UFRGS, Cx. P. 15001, 91540-970, Porto Alegre, RS, Brazil. ABSTRACT – This paper presents three new genera and species of pygocephalomorph crustaceans from outcrops in Pantano Grande and Minas do Leão counties, State of Rio Grande do Sul, Southern Brazil. The silty shales present molds of mostly articulated crustaceans, in association with Glossopteris, insect remains and fish scales. These new genera expand the number of Pygocephalomorpha from the Irati Formation and contribute to the knowledge on the Gondwanan Malacostraca species. Key words: Paleozoic, crustaceans, Malacostraca, taxonomy, Paraná Basin, Gondwana. RESUMO – Este trabalho apresenta três novos gêneros e espécies de crustáceo pigocefalomorfo provenientes de afloramentos localizados nos municípios de Pantano Grande e Minas do Leão, Estado do Rio Grande do Sul, sul do Brasil. Os folhelhos síticos apresentam moldes de crustáceos, principalmente articulados, em associação com Glossopteris, restos de insetos e escamas de peixe. Os novos táxons aumentam o número de Pygocephalomorpha da Formação Irati e contribuem para o conhecimento das espécies de Malacostraca do Gondwana. Palavras-chave: Paleozoico, crustáceos, Malacostraca, taxonomia, Bacia do Paraná, Gondwana. INTRODUCTION (Eucarida). The cephalothorax is mysid-like, with eight sternites and biramous appendages, the first pair being Pygocephalomorph crustaceans have been known since modified into maxillipeds in many species. In addition, the the second half of the 19th century from the Carboniferous females bear oöstegites – modified epipodites that hold a of England and Scotland (Huxley, 1857; Salter, 1861, 1863; brood pouch, or marsupium, where the eggs develop until Prestwich, 1840; Peach, 1883). During the 20th century, reaching juvenile stage. records were found in the Carboniferous and Permian of The pleon is decapod-like, with a length and width the United States of America (Brooks, 1962; Schram, 1988; sub-equal to or greater than the cephalothorax, a developed Hotton et al., 2002; Irham et al., 2010) and South Africa pleomere, large biramous uropods, and a telson bearing (Rogers & Du Toit, 1909; Broom, 1931; Fabre & Huard, a terminal spine (furca). The cephalothorax morphology 1967); and in the Permian of Russia (Schram, 1978), China (Schram, 1984) and phylogenetic analysis (Taylor et al., (Taylor et al., 1998), South America (Clarke, 1920; Beurlen, 1998) indicate that Pygocephalomorpha is a fossil suborder 1931, 1934, 1953; Mezzalira, 1954; Vieira et al., 1991; Piñeiro of Mysida, which are benthic crustaceans (Schram, 1986). et al., 2012a), and most recently Italy (Jones et al., 2015). The systematic position of Pygocephalomorpha is based This fossil order presents Eumalacostraca basal mostly on Laurasian taxa, since Gondwanan species are characters such as tagmosis of the body into a cephalothorax described from sparse and incomplete material, many of and pleon, thoracic biramous appendages with only one them being established on the basis of fragmentary pieces of segment in the protopod, and a carapace completely covering crustacean fossils (Pinto & Adami-Rodrigues, 1996), leading the cephalothorax (Brooks, 1969). Schram (1974) defined to misinterpretations. Pygocephalomorpha as crustaceans possessing a carapace Traditionally, three genera and six species are recognized with branchiostegal development; a pleon equal in length from Brazil: Paulocaris pachecoi Clarke, 1920; P. marianoi to the thorax or reduced; oöstegites in females; and well- Beurlen, 1953; Liocaris huenei Beurlen, 1931; L. angusta developed caudal spines and furca. When proposing the Beurlen, 1931; Pygaspis brasiliensis Beurlen, 1934 and taxon Pygocephalomorpha, Beurlen (1930) questioned its P. quadrata Beurlen, 1934, which is currently under revision systematic position, since its representatives share characters (Adami-Rodrigues & Pazinato, pers. comm.). The Brazilian with both recent Mysida (Peracarida) and Decapoda forms are from the Irati Formation (Artinskian/Kungurian) of 389 390 REVISTA BRASILEIRA DE PALEONTOLOGIA, 19(3), 2016 the Paraná Basin, known for oil shales and mesosaurid fossils described (Permocaris and Iraticaris), plants, insects, and fish (Holz et al., 2010). scales. Overlying this bed there is 10 cm of non-fossiliferous Pygocephalomorphs occur throughout the whole reddish mudstone, which is followed by another layer with 20 geographic range of the Irati Formation, from the Center to cm of beige silty shale, bearing the same fossils as found in Southern Brazil, Goiás (Vieira et al., 1991), São Paulo (Clarke, the basal one. Above the siltic shale, there is 1 m of reddish 1920; Beurlen, 1931; Mezzalira, 1954), Paraná (Mezzalira, mudstone, covered by 1.5 m of fine sandstones with small- 1954), Santa Catarina (Beurlen, 1934; Pinto, 1971), and Rio sized cross-bedding. The stratigraphic column ends with 3 m Grande do Sul states (Beurlen, 1953; Pinto, 1955; Adami- of soil (Figure 2). The locality from which the fossils were Rodrigues & Pinto, 2000). They are also found in Uruguay, collected is currently covered by rubble deposited by Pantano from the Mangrullo Formation, Paraná Basin, the stratigraphic Grande City Hall. equivalent of the Irati Formation (Piñeiro et al., 2012a). Pinto (1955) discovered this outcrop and described it as This paper describes three new genera and species of the first Palermo Formation (Upper Carboniferous) outcrop Pygocephalomorpha from the Irati Formation, from State in RS. At that time, the few crustacean fossils found led the of Rio Grande do Sul (RS), Southern Brazil. The new author to classify them as basal pygocephalomorphs. Later, occurrences of crustaceans presented in this paper extend Pinto (1972) concluded that the fossils were actually new the record of pygocephalomorphs in the Paraná Basin and species and the outcrop belonged to the Irati Formation. contributes to understanding the distribution and diversity Outcrops II and III are small-sized exposures (Figure 3). of the taxon in Gondwana. They are on either side of BR-290, at old Rio Pardo road, about 1.5 km from Pantano Grande County and 2 km apart GEOLOGICAL SETTING from each other. Outcrop II is 1.5 km south of BR-290 and at its base there are siltic shales with slump structures, which The fossils were collected from three outcrops in Minas are followed by gray siltic shales interbedded with yellowish do Leão and Pantano Grande counties, RS, Brazil (Figure 1). limestone lenses where crustaceans (Pittinucaris) and fish Outcrop I is a road-cut on the BR-290 (Porto Alegre– scales are found. According to Figueiredo (1972), in state of Uruguaiana way), Minas do Leão County, about 2 km west Rio Grande do Sul, the Palermo and Irati formations have a of Capão da Roça creek. The outcrop is about 90 m long and gradational contact. Figueiredo (1972) described the Palermo 6 m high, and at its base there is 20 cm of beige silty shale, Formation as having beds mostly disturbed by slumping, green when wet, containing two of the crustaceans here while the Irati Formation has, in its basal portion, yellowish Figure 1. Map of State of Rio Grande do Sul highlighing Minas do Leão and Pantano Grande counties. Geological hammers mark the locations of outcrops I, II and III. ADAMI-RODRIGUES ET AL. – PYGOCEPHALOMORPHA FROM THE IRATI FORMATION, BRAZIL 391 Figure 2. Stratigraphic column of outcrop I, Minas do Leão County, RS. Two of the crustacean species (Permocaris and Iraticaris) are found in the silty shale beds, along with plants, insects, and fish scales. Adapted from Adami-Rodrigues (1998). Figure 3. Stratigraphic column from the Pantano Grande area according to Figueiredo (1972), indicating stratigraphic position of outcrops II and III. Adapted from Adami-Rodrigues (1998). limestone lenses, and alternations of thin layers of light and RESULTS dark thin siltic shales. Based on this interpretation, the authors consider this outcrop as belonging to the basal portion of the The fossils comprise several crustaceans, most of them Irati Formation in State of Rio Grande do Sul. articulated and a few semi-articulated. In the semi-articulated Outcrop III is 4 km north of BR-290 and exhibits about specimens, the cephalothorax–pleon or the cephalothorax– 4 m of rock succession comprising brown paper-like shales. appendage joints were broken. The crustaceans are preserved The fossils include one species of crustacean (Iraticaris), as molds, mostly presenting ventral views, possibly in the Glossopteris, and fish scales. The paper-like shales are death position. However, a few isolated remains show dorsal followed by silty shales with cone-in-cone structures. The views, such as carapaces and pleons. Pittinucaris fossils are lithology and fossils recorded in outcrop III were correlated the only ones that show signs of compression. At outcrop I, we with the Irati Formation through borehole 180 of the DACM collected blocks with dispersed crustaceans (Permocaris and for State of Rio Grande do Sul (Machado & Castanho, 1956; Iraticaris), but that
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