Biomechanical evidence suggests extensive eggshell thinning during incubation in the Sanagasta titanosaur dinosaurs

Abstract

The reproduction of titanosaur dinosaurs is still a complex and debated topic. Their Late Cretaceous nesting sites are distributed worldwide and their eggs display substantial morphological variations according to the parent species. In contrast to the typical 1.3–2.0 mm thick shells common to eggs of most titanosaur species (e.g., those that nested in Auca Mahuevo, Tama, Toteşti or Boseong), the Cretaceous Sanagasta eggs of Argentina display an unusual shell thickness of up to 7.9 mm. Their oviposition was synchronous with a palaeogeothermal process, leading to the hypothesis that their extra thick eggshell was an adaptation to this particular nesting environment. Although this hypothesis has already been supported indirectly through several investigations, the mechanical implications of developing such thick shells and how this might have affected the success of hatching remains untested. Finite element analyses estimate that the breaking point of the thick-shelled Sanagasta eggs is 14–45 times higher than for other smaller and equally sized titanosaur eggs. The considerable energetic disadvantage for piping through these thick eggshells suggests that their dissolution during incubation would have been paramount for a successful hatching.

Life and reproduction of titanosaurians: Isotopic hallmark of mid-palaeolatitude eggshells and its significance for body temperature, diet, and nesting

“…The fact that eggshells are systematically found in association with hydrothermal features, together with the very common occurrence of overly thick eggshells (which necessarily implies massive extrinsic dissolution before the young could hatch) led to the hypothesis that some titanosaurians used hydrothermal heat for egg incubation (cf. Grellet-Tinner and Fiorelli, 2010;Hechenleitner et al, 2018b). In this context, the unusual thickness of the eggshells can be viewed as an adaptive trait compensating for the strong dissolution of the outer shell under the acidic conditions prevailing in most hydrothermal environments where silica is deposited.…”