Isotopic niches of aquatic and semiaquatic predators from the cretaceous of the São Luís-Grajaú Basin, Brazil

Abstract

Since the 20th century, methodologies involving isotopic techniques have been used to study from the physiology of organisms to meteorological events that may influence the ecology of animals and plants, especially WHERE there is no possibility of direct observation of their feeding behaviors, as in the case of extinct animals. In this work, we studied the carbon and oxygen stable isotopes of fossils found in one of the outcrops of the Alcântara Formation, part of the São Luís-Grajaú Basin, Maranhão: the Coringa Flagstone, located on Cajual Island, dated to the UpperCretaceous (Cenomanian), in order to ascertain how the competition relationships were, from analyzingamplitude and niche overlap of the aquatic and semi-aquatic predators of the region (carnivorous dinosaurs, pterosaurs,and elasmobranchs), taking into account that the concentrations of δ13C vary according to their food, and those of δ18O vary mainly with the temperature and the available water sources, using and comparing mathematical models and Bayesian methods. As results, we noticed a high competition among the studied taxa, even when taking into account the differences presented by the different methods applied, which corroborates the hypothesisthat all carnivorous archosaurs from theCoringa Flagstone had semi-aquatic habits and that they competed among themselves, besides being able to add to the discussion about the competition between carcharodontosaurids and spinosaurids. As a conclusion, Bayesian methods and mixed mathematical models can be used in isotopicpaleontology in a complementary way.