Femoral diversity in titanosaur sauropods from the Villalba de la Sierra Fm. (Central Spain): Implications for the characterization of faunal turnover in the Ibero-Armorican Late Cretaceous

Abstract

The late Campanian-Maastrichtian in the Ibero-Armorican domain is rich in titanosaurian fossils. The sauropod remains exhibit a high degree of morphological variability, especially in the commonly-found appendicular elements. The phylogenetic relationships of the Ibero-Armorican titanosaurs are still uncertain but we do know that they experienced a Campanian-Maastrichtian herbivorous faunal turnover. It is probable that the small-to-medium-sized Lirainosaurinae-dominated faunas of the Campanian were replaced by late–early Maastrichtian large-bodied lithostrotian dominated faunas. In this context, the Villalba de La Sierra Formation has yielded an abundant sample of medium-to-large sized titanosaurs. In this study we analyze the morphological variability in the appendicular skeleton of the titanosaurs from the Campanian-Maastrichtian Ibero-Armorican domain. We follow previous attempts to classify the commonly-found isolated titanosaurian femora and expand the proposed methodology. The use of combined phenotypic characters and linear morphometrics can be helpful to analyze the morphological variability and diversity of the Ibero-Armorican titanosaurs. Our findings corroborate the presence of at least two exclusive morphotypes in the Lo Hueco fossil site and one exclusive morphotype in the Poyos site, as well as the presence of previously defined Lirainosaurinae across the Pyrenees during the Campanian-Maastrichtian. The Villalba de La Sierra Formation titanosaurs are also clustered with large-bodied late Maastrichtian titanosaurs. It is possible that either the large-bodied late–early Maastrichtian immigrants, with possible Gondwanan affinities, entered the Iberian Peninsula much earlier or that this group was already present at least during the Campanian-Maastrichtian transition, as the small-sized Lirainosaurinae declined.