The book discusses the influence of temperature on the incubation of marsh caiman (Caiman crocodilus yacare) eggs in the Pantanal of Mato Grosso do Sul, Miranda and Abobral sub-regions. This species has a temperature-dependent sex determination mechanism (TSD). Using thermometers installed at different depths in a forest nest, we found that the temperature inside the chamber was significantly higher than the outside temperature, and all the chicks sexed after hatching were females. We developed a suitable incubation system to verify the influence of thermal fluctuations on the sex determination of the species. In the laboratory, we subjected eggs to 5 different ranges of daily fluctuations. The sex of the chicks was determined by histological analysis of the gonads and, in all treatments, only females were born, indicating that these ranges of daily thermal oscillation do not interfere with sex determination.