Tafonomia de Fósseis de Vertebrados (Megafauna Extinta) Encontrados nas Barrancas do Arroio Chuí e Linha de Costa, Rio Grande do Sul, Brasil

Resumo

The present work describes the taphonomy of the extinct mammals’ fossils (Pleistocene megafauna) found in Chuí creek embankment, in Rio Grande do Sul State, southern Brazil and compares them to the mammals’ fossils occurring along the shoreline of the same State. These mammals lived during the Upper Pleistocene (Lujanense land-mammal period) about 120000 years ago; the fossils that occurs along Chuí creek and the ones found along the shoreline suffered deposition in coastal lagoons, originated during events of sea transgression-regression, althought the last ones are now found in subaquatic environments, preserved in submerged biodetritic banks along the coast and are being thrown onto the beach during storm events. These fossils are extremely hard and dark, due to substitution of the bone’s original calcium phosphate by silicates and oxides. While these fossils are found fragmented on the beach due to wave action and transport, the fossils occurring along Chuí creek embankment are well preserved, indicating that they haven’t suffered significant transport; the latter show light colour and more fragility due to lixiviation. Articulated parts of mammals are found, and many bones show grooves and scratches, suggesting the action of scavengers after death. They are found in situ at a depth of 2,5-3,5m in lacustrine sediments of Pleistocene origin in the Chuí creek embankment and above a layer of oxidated beach sands which show parallel stratification and galleries of the Callianassa crustacean.