The Auca Mahuevo nesting site (Upper Cretaceous, Argentina), revisited: new insights into the structural diversity and incubation mode of titanosaur (Dinosauria, Sauropoda) eggs

The Argentinian Auca Mahuevo site is well known for its fossil eggs associated to titanosaur embryonic remains. Although the eggs are distributed across four stratigraphically distinct layers, only a few broad comparisons have been made between the materials from each layer. To explore the structural diversity of the Auca Mahuevo eggs, we examined multiple specimens from the two uppermost layers of the site and compared their quantitative characteristics through statistical analyses. Additionally, to investigate the reproductive behaviour of the progenitor titanosaurs, we estimated the water vapour conductance and porosity of various eggs from both Auca Mahuevo layers. The specimens from the two layers only differ significantly in their eggshell thickness and mean size of their ornamentation nodes. Furthermore, the porosities and conductances of the eggs align, on average, with the expected values for modern archosaur eggs incubated in open nests. This distinguishes the Auca Mahuevo eggs from similar specimens found in France, Spain, Romania and Argentina, which exhibit porosities and conductances comparable to those of modern archosaur eggs incubated in covered nests. These findings not only enhance our understanding of the structural variation of the Auca Mahuevo eggshells but also provide new insights into the diversity of sauropod reproductive behaviour.