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The Tacuarembo Formation has yielded a fossil assemblage that includes the best known body fossils, consisting of isolated scales, teeth, spines, and molds of bones, recovered from thin and patchy bonebeds, from the Botucatu Desert, Parana Basin, South America. The remains are preserved in the sandstones widespread around the city of Tacuarembo. We propose a new formalized nomenclature for the Tacuarembo Formation, naming its "Lower" and "Upper" members as the Batovi (new name) and Rivera (new rank) members, respectively. An assemblage zone is defined for the Batovi Member (fluviolacustrine and aeolian deposits). In this unit, the freshwater hybodontid shark Priohybodus arambourgi D’Erasmo is well represented. This species was previously recorded in Late Jurassic-Early Cretaceous units of the Sahara and the southern Arabian Peninsula. Globally considered, the fossil assemblage of this member (P. arambourgi, dipnoan fishes, Ceratosaurus-like theropods, and conchostracans) is indicative of a Kimmeridgian-Tithonian age, which in combination with the stratigraphic relationships of the Tacuarembo Formation with the overlying basalts of the Arapey Formation (132 My average absolute age) implies that the latter was deposited during the Kimmeridgian-Hauterivian interval. (C) 2009 Elsevier Ltd. All rights reserved.