Fossil evidence of exceptionally large egg-clutches sheds light on reproductive diversity in Late Cretaceous crocodyliforms from Brazil

The Upper Cretaceous units of the Bauru Group have provided a comprehensive fossil record of eggs and nests belonging to different reptilian clades, such as turtles, crocodyliforms, and dinosaurs. Here, we report the discovery of several egg-clutches from the Adamantina Formation (Bauru Group), cropping out in the city of Presidente Prudente (São Paulo State, Brazil). The new discovery represents three egg clutches, totaling 83 eggs, plus numerous isolated eggshells. The spatial arrangement of the eggs within the clutches is like that observed in different species of extant crocodyliforms, an arrangement that results from the construction of a relatively narrow hole within a substrate mixed with leaf litter. An important feature of one of the clutches (MPM 447) is that it contains a large number of eggs (at least 47), thus representing the largest Mesozoic crocodyliform egg clutch ever found. SEM images of the external surface revealed a high pore density, suggesting that thicker and more porous eggs facilitate water loss, compensating for deposition in more humid settings. The set of attributes converges with structures described for crocodyliforms. In connection with studies conducted on the Bauru Group, the correlation with Notosuchia elucidates broader aspects of the adaptation of this clade, which includes organisms specialized in both terrestrial environments and more humid habitats. The new discovery shows new evolutionary implications for one of the world's most diverse fossil crocodylomorph faunas, revealing more complex and successful reproductive habits with potential adaptations to occasionally wetter environments.