Eggshell sites from the Cretaceous–Tertiary transition in south-central Pyrenees (Spain)

Abstract

Near one hundred fossil sites containing dinosaur and avian eggs and eggshells have been recorded from coastal and non-marine deposits of late Cretaceous to late Paleocene age in South-central Pyrenees. Five eggsite types have been distinguished, three of them with autochthonous and two with allochthonous assemblages. The egg-bearing sediments consist in marine sandstones from the Aren Formation, and coastal and non-marine red beds from the Tremp Formation. Inferred nesting paleoenvironments range from sand beaches and strand plain at the seashore (Aren Sandstone sites), to tidal mud-flats in lagoonal margins (La Posa Grey Marls, lower Member of the Tremp Formation), and perilagoonal, estuarine and alluvial flood plains (bioturbated siltstones, variegated claystones, sandstones and conglomerates of the Tremp red beds). About thirty ootaxa, mainly from tubospherulitic, prismatic and ratite morphotypes have been observed, which greately overpass the dinosaur and avian diversity deduced from bones. These sites indicate a nest-fidelity reproductive behaviour for Pyrenean dinosaurs and birds. A decrease in abundance and diversity is recorded from late Campanian to Maastrichtian times, while a recovery occurs in late Paleocene.