Dinosaur ichnofauna of the Upper Jurassic/Lower Cretaceous of the Parana Basin (Brazil and Uruguay)

Upper Jurassic and Lower Cretaceous sedimentary layers are represented in the Brazilian Parana Basin by the fluvio-aeolian Guard Formation and the Botucatu Formation palaeoerg, respectively, overlapped by the volcanic Serra Geral Formation. In Uruguay, the corresponding sedimentary units are named Batovi and Rivera Members (both from the Tacuarembo Formation), and the lava flows constitute the Arapey Formation (also in Parana Basin). Despite the lack of body fossils in the mentioned Brazilian formations, Guara/Batovi dinosaur fauna is composed of theropod, ornithopod and wide-gauge sauropod tracks and isolated footprints, as well as theropod teeth. In turn, the Botucatu/Rivera dinosaur fauna is represented by theropod and ornithopod ichnofossils smaller than those from the underlying units. The analysis of these dinosaur ichnological records and comparisons with other global Mesozoic ichnofauna indicates that there is a size reduction in dinosaur fauna in the more arid Botucatu/Rivera environment, which is dominated by aeolian dunes. The absence of sauropod trackways in the Botucatu Sandstone fits with the increasingly arid conditions because it is difficult for heavy animals to walk on sandy dunes, as well as to obtain the required amount of food resources. This comparison between the Upper Jurassic and Lower Cretaceous dinosaur fauna in south Brazil and Uruguay demonstrates the influence of aridization on the size of animals occupying each habitat. (C) 2015 Elsevier Ltd. All rights reserved.