Fondevilla, V.

In south-western Europe, the uppermost Cretaceous continental deposits in the different sedimentary basins of Iberia (Portugal and north and central Spain), the Pyrenees (Spain and France) as well as Languedoc and Provence (southern France) provide one of the few terrestrial records that allow a comprehensive study of the Campanian-Maastrichtian dinosaur assemblages. For the last years the southern Pyrenees has been the target of intense geological, palaeontological and geochronological research. Hundreds of fossil localities are now framed in high-resolution lithological sections. The succession of these sites, most of them located in the Tremp Syncline, is based on the physical correlation of rock bodies, as permitted by the general outcropping conditions. Outside this syncline, correlation is supported by geochronologic and biostratigraphic data (mainly magnetostratigraphy and planktic foraminifera biostratigraphy). The integration of the entire dataset sheds new light on the Maastrichtian dinosaur turnover, characterized by a shift from a sauropod-dominated to a hadrosauroid-dominated faunal assemblage. This turnover was progressive and involved immigrants from North America, Eurasia and Gondwana, which probably reached the study area after a sea level drop. This faunal change was mainly triggered by the arrival of lambeosaurine hadrosauroids, a group that rapidly displaced the rest of the herbivorous clades of the region. Some of the extinction events suffered by the “pre-turnover” faunas during the Maastrichtian coincide with marine isotopic and sea-level drop events, suggesting that faunal competition was not the only cause of the observed changes in dinosaur composition. Despite this faunal replacement, the resulting ecosystem after the turnover shows no major loss of biodiversity before the Cretaceous-Paleogene extinction event.

The L'Espinau site is a dinosaur bonebed fromthe Upper Cretaceous of the South-Central Pyrenees (north-eastern Spain) that have provided hundreds of bone remains attributed to hadrosauroids, together with a rich assemblage of herpetofauna, fish and microflora. Magnetostratigraphy calibrated the site with the early late Maastrichtian, and the combined sedimentology, stable isotope geochemistry and palaeoecology revealed that this fossil site formed in a lagoon, in which a mixed freshwater-brackish palaeoenvironment was developed. This setting displays a south-north charophyte zonation from freshwater (Clavator brachycerus-dominated assemblage) to brackish or eurihaline conditions (Feistiella malladae-dominated assemblage), revealing a palaeoenvironment change towards the coast. Sedimentology and taphonomy (bidirectional arrangement of long bones, abrasion and disarticulation) indicate that the L'Espinau site is the result of a cohesive mass flow event originated very close to the sea. This process entrained and mixed fauna from both the terrestrial and the brackish/marine environment of a lagoon. An increasing of the water runoff (e.g. by intense rainfall) reworking poorly consolidated sediments is considered here as the most probable triggering mechanism. Mass flow-hosted bonebeds are commonly linked to fluvial palaeoenvironments, so our study case is a rare example of bones accumulating near the sea. This study adds evidence that hadrosauroids inhabited littoral environments during the Maastrichtian in the southern Pyrenean area.