Do ontogenetic changes during incubation interfere with the interpretation of incubation mode in dinosaur eggs?

Abstract

Dinosaurs are oviparous reptiles that belong to Archosauria and whose closest modern relatives are crocodiles and birds. This is why, to shed light on the study of dinosaur reproduction, we conducted a test with the species Caiman latirostris (Crocodylia), a living archosaur. This paper focuses on the study of the embryos’ effect on the eggshells of Caiman latirostris during incubation. A total of 30 eggs from four nests including both embryonated and non-embryonated eggs were artificially incubated under the same conditions (incubation medium and temperature) to observe changes in eggshell structure throughout embryonic development. We found significant differences between eggs, in the embryonated eggshells we observed that the continuous calcium layer, became thinner, while at the same time we recorded an increase in the porosity of the eggshells both in the polar and equatorial regions. These changes could explain the variability recorded in fossil deposits with broods, where shells of the same oospecies were found at different levels and with differences in porosity and thickness. The results of this study will contribute to the methodology behind the inference of nesting environment and nesting strategies (buried, semi-buried or exposed) for fossil eggs, which typically utilises calculations of water vapour conductance.