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-EVIDENCE OF GREGARIOUS BEHAVIOUR IN PALEOBURROWS OF MYLONDONTIDAE (GIANT SLOTHS). This article presents evidence of gregarious behavior in paleoburrows attributed to giant sloths. Paleoburrows are biogenic structures in the shape of galleries and halls excavated by extinct giant mammals that lived in the Pliocene and Pleistocene. In the case discussed here, they were excavated in rocks composed by neoproterozoic metadiamictites with hematite of the Macaúbas Group (Nova Aurora Formation). The rocks, of glacial origin, underwent metamorphism, were strongly cemented by hematite and exhibit high hardness. In the north of Minas Gerais, were identified new paleoburrows distributed in a grouped manner, located in valleys with steep slopes embedded in geological faults. In each group, the paleoburrows are arranged on both sides of the valley, facing at each other. At the walls and roofs of the paleoburrows, there are hundreds of claw marks, forming parallel double marks and intertwined marks. Silicone molds of the marks were compared with hand bones of Valgipes sp. (Mylodontidae) deposited in the collection of PUC-MG; the size and morphology of the double marks allowed to attribute these paleoburrows to digging mylodontids (two-toed giant sloths). At the lateral walls of the paleoburrows we identified several polished surfaces of elliptical shape, each one with a diameter of approximately 2.4 m. These polished surfaces aroused due to the abrasive action of the giant sloths´ fur at their resting place. A single paleoburrow may show from 1 to 3 of these elliptical surfaces, suggesting a gregarious behavior of the sloths, who slept together in these spaces.Key words: megafauna, Quaternary, Minas Gerais, ichnofossils.RESUMO -Este estudo apresenta evidências de vida gregária em paleotocas atribuídas às preguiças-gigantes. As paleotocas são estruturas biogênicas na forma de galerias e salões escavados por mamíferos gigantes extintos que viveram no Plioceno e Pleistoceno. Foram escavadas em rochas compostas por metadiamictitos hematíticos neoproterozoicos do Grupo Macaúbas (Formação Nova Aurora). As rochas de origem glacial sofreram metamorfismo, são fortemente cimentadas por hematita, e apresentam elevada dureza. No norte de Minas Gerais foram identificadas novas paleotocas distribuídas de forma agrupada, em vales de encostas íngremes encaixados em falhas. Em cada agrupamento as paleotocas estão dispostas nos dois lados dos vales, umas em frente às outras. Nas paredes e no teto das paleotocas há centenas de marcas de garras, formando marcas duplas paralelas e marcas entrelaçadas. Moldes em silicone das marcas foram comparados com ossos das mãos de Valgipes sp. (Mylodontidae) depositados na coleção da PUC-MG; o tamanho e morfologia das marcas duplas permitem atribuir estas paleotocas a milodontídeos cavadores (preguiças-gigantes de dois dedos). Nas paleotocas foram identificadas diversas superfícies polidas de formato elíptico, com cerca de 2,4 m de diâmetro, atribuídas ao desgaste da rocha devido ao atrito da pelage...

A regional survey of the caves of the state of Rio Grande do Sul, Brazil, listed hundreds of caves with varied origins. Among these, we identifi ed two large caves with special characteristics, one located in the city of Santa Cruz do Sul and the other in the municipality of Vale Real. Both evolve in an approximately horizontal plane, extend tens of meters into the interior of the respective elevations, and do not show any signs of present or past underground drainage. Concave surfaces on the walls stand out in their morphologies, which suggest that the caves originally constituted a system of ellipsoidal chambers, each chamber with original height of approximately 1.5 m and diameter between 3.5 and 7 m. The individual chambers were connected by relatively short tunnels.These chambers are best preserved in the cave of Santa Cruz do Sul; the cave of Vale Real appears to have been much disfi gured, both because of inorganic processes and anthropogenic action. The general characteristics of these two caves enable us to propose that they originated from the activity of digging ground sloths of the South American Megafauna. Their dimensions suggest that they were excavated and inhabited not by individual animals, but by groups of sloths. The original polished walls suggest that the caves were used for extended periods, possibly in the order of centuries. Their morphology is so different from other tunnel systems that were excavated by the Megafauna and found in southern Brazil, that we suggest that this morphology of chamber systems is associated with a specifi c species of ground sloth, whose identifi cation will be very diffi cult.

In the last ten years, more than 1,500 large burrows have been discovered in southern and southeastern Brazil, dug in rocks that include weathered granitic and basaltic rocks, sandstones, and other consolidated sediments. Their presence in geological units of Plio-Pleistocene age suggests that large extinct mammals produced these structures. The internal walls exhibit scratches and grooves left by the animals that inhabited these structures. The burrows are straight or slightly sinuous tunnels that measure up to tens of meters in length. One smaller type measures up to 1.5 meter in diameter, and the larger type can reach 2 meters in height and 4 meters in width, suggesting that such structures have been produced by at least two kinds of organisms. This contribution proposes a classification for these ichnofossils under the generic designation Megaichnus igen. nov., consisting of two ichnospecies identified so far: M. major and M. minor ispp. nov. Although the exact identity of the producers of the burrows is yet unknown, the dimensions and morphology point to ground sloths and giant armadillos.

A discussão sobre a origem das Províncias de Basaltos de Platô Continentais tem como um de seus elementos mais importantes o volume do magma mobilizado. Em relação às rochas da Formação Serra Geral na Bacia do Paraná (América do Sul), a maioria dos autores cita uma extensão de 1.200.000 km2 e um volume de aproximadamente 800.000 km3 . O mesmo volume é usado frequentemente para a Província de Basaltos de Platô Continental Paraná-Etendeka, da qual a Formação Serra Geral constitui a maior parte. Nós investigamos a precisão desses números através de uma revisão histórica completa acerca de sua origem. Verificamos que o valor relativo à extensão, de 1.200.000 km2 , é apenas uma estimativa apresentada em 1934 e que o volume de 800.000 km3 foi obtido multiplicando este valor de extensão por uma estimativa da espessura média dos derrames de lava de 650 metros apresentada em 1966. Usando um mapa recente, verificamos que a área coberta por rochas vulcânicas na Bacia do Paraná é de apenas 917.000 km2 (+- 15.000 km2 ). Através de mapas de isópacas de 1987 e 1990, calculamos o volume das rochas extrusivas como sendo de pelo menos 450.000 km3 e que o volume referente aos corpos intrusivos do tipo sill é de pelo menos 112.000 km3 . Através destas estimativas, o volume de rochas da Formação Serra Geral deve ser considerado como sendo superior a 600.000 km3 . A Província de Basaltos de Platô Continental Paraná-Etendeka como um todo possui um volume de no mínimo 1.700.000 km3 .