Have the ontogenetic changes during incubation interfere with dinosaur interpretation of incubation mode?

FERNÁNDEZ, M; PIAZZA, MILA V.; SIMONCINI, M.

Congreso; Reunión de Comunicaciones de la Asociación Paleontológica Argentina; 2022

Asociación Paleontológica Argentina

Dinosaurs are oviparous reptiles that belong toArchosauria and whose closest modern relatives are crocodiles and birds. Thisis why, to shed light on the study of dinosaur reproduction, we conducted atest with the species Caiman latirostris,a living archosaur. The aim of this study focusses on the embryos’ effect onthe eggshells of Caiman latirostriseggs during incubation. A total of 30 eggs from four nests including bothembryonated and non-embryonated eggs were artificially incubated under the sameconditions (incubation medium and temperature) to observe changes in eggshellstructure throughout embryonic development. We found significant differencesbetween embryonated and non-embryonated eggs. In the embryonated eggshells weobserved that the continuous calcium layer, also known as the parameter"shell thickness without ornamentation", became thinner, while at thesame time we recorded an increase in the porosity of the eggshells both in thepolar and equatorial regions. These changes could explain the variabilityrecorded in fossil deposits with broods, where shells of the same oospecieswere found at different levels and with differences in porosity and thickness.The results of this study will contribute to the methodology behind theinference of nesting environment and nesting strategies (buried, semi-buried orexposed) for fossil eggs, which typically utilizes calculations of water vaporconductance. Additionally, our findings will allow future researchers toredefine oospecies boundaries, since both shell thickness and conductance changeduring incubation.