Palaeobiogeography of the Bauru Group, a dinosaur-bearing Cretaceous unit, northeastern Parana Basin, Brazil

Abstract

The integration of sedimentologic, palaeontologic and petrologic data allows interpretation of the palaeoclimatic evolution in the northeastern Parana Basin of Brazil during the Late Cretaceous. The study of the dinosaur-bearing Bauru Group in Minas Gerais State in two areas, the Uberaba and the Prata regions, allows us to discuss biogeographic aspects related to the dinosaurian fauna in Brazil. The terrigenous and carbonate rocks of the Bauru Group were deposited in fluvial, eolian and lacustrine environments in a semi-arid to arid climate with marked seasonality in which dry periods alternated with periods of heavy rain. The climatic evolution during this period of deposition can be divided in two intervals: Time 1 (T1), Coniacian–Campanian, when the Uberaba and Adamantina Formations were deposited, and Time 2 (T2), mainly Maastrichtian, when the Marı́lia Formation was deposited. During both intervals, the humidity was higher in the Uberaba region than in the Prata region, eolian deposits and caliche profiles being present in the latter, but not in the former. Extensive skeletal deposits and nesting sites indicate that favourable environmental conditions for the dinosaurian fauna existed in the Uberaba region, while the Prata region was probably a gateway to fauna migrating from the northeastern Parana Basin to Argentina and Bolivia. It has been suggested that Cretaceous dinosaur biogeography in the Southern Hemisphere was largely controlled by the sequential breakup of Gondwana. Locally, the migration and preferential distribution of dinosaurian habitats were controlled by climatic conditions, geographic topography and eventually by volcanic activity.