Isotopic hallmark of mid-palaeolatitude titanosaurian eggs

Abstract

Titanosaurian (Dinosauria - Neosauropoda) dinosaur eggshells are an important part of the fossil record of that clade, well-suited for palaeoecological reconstructions based on oxygen and carbon stable isotope analyses. Their resistance to diagenesis makes them valuable substitutes of bioapatite remains when highly mineralized skeletal remains such as teeth are scarce or absent. We present a new set of conventional (δ18O and δ13C) and clumped (Δ47) stable isotope compositions of titanosaurian eggshells from the recently discovered Late Cretaceous nesting site of Quebrada de Santo Domingo, La Rioja Province, northwestern Argentina. Comparisons with isotopic data from other titanosaurian nesting sites worldwide reveal clear clusters, one of which is interpreted as the isotopic hallmark for well-preserved, mid-palaeolatitude titanosaurian eggs (δ13CVPDB = -15 to -11 ?; δ18OVSMOW = 27 to 33 ?). This implies that the physiological processes linked to egg formation across Titanosauria were comparable, and that representatives of that clade needed similar environmental conditions for nesting, independently of their geographical location. The definition of an isotopic range for well-preserved titanosaurian eggshells shall help to recognize close-to-pristine material, especially when the alteration is cryptic and did not affect the microstructure of the oological remains. Additionally, we offer new data on the body temperature of titanosaurians suggesting that it may have been higher than previously published. Finally, we show that Riojan titanosaurians needed conditions more arid than the long-term average for nesting, further supporting the hypothesis that these dinosaurs were breeding migrants.