The Tetrapod Fossil Record from the Uppermost Maastrichtian of the Ibero-Armorican Island: An Integrative Review Based on the Outcrops of the Western Tremp Syncline (Aragón, Huesca Province, NE Spain)

Manuel Pérez-Pueyo,Diego Castanera,José Manuel Gasca,Penélope Cruzado-Caballero,Eduardo Puértolas-Pascual,Miguel Moreno-Azanza,Bernat Vila,José Ignacio Canudo,Beatriz Bádenas

doi:10.3390/geosciences11040162

Abstract

The South-Pyrenean Basin (northeastern Spain) has yielded a rich and diverse record of Upper Cretaceous (uppermost Campanian−uppermost Maastrichtian) vertebrate fossils, including the remains of some of the last European dinosaurs prior to the Cretaceous-Paleogene (K-Pg) extinction event. In this work, we update and characterize the vertebrate fossil record of the Arén Sandstone and Tremp formations in the Western Tremp Syncline, which is located in the Aragonese area of the Southern Pyrenees. The transitional and continental successions of these sedimentary units are dated to the late Maastrichtian, and exploration of their outcrops has led to the discovery of numerous fossil remains (bones, eggshells, and tracks) of dinosaurs, including hadrosauroids, sauropods, and theropods, along with other tetrapods such as crocodylomorphs, testudines, pterosaurs, squamates, and amphibians. In particular, this fossil record contains some of the youngest lambeosaurine hadrosaurids (Arenysaurus and Blasisaurus) and Mesozoic crocodylomorphs (Arenysuchus and Agaresuchus subjuniperus) in Europe, complementing the lower Maastrichtian fossil sites of the Eastern Tremp Syncline. In addition, faunal comparison with the fossil record of Hațeg island reveals the great change in the dinosaur assemblages resulting from the arrival of lambeosaurine hadrosaurids on the Ibero-Armorican island, whereas those on Haţeg remained stable. In the light of its paleontological richness, its stratigraphic continuity, and its calibration within the last few hundred thousand years of the Cretaceous, the Western Tremp Syncline is one of the best places in Europe to study the latest vertebrate assemblages of the European Archipelago before the end-Cretaceous mass extinction.

Highlights

The Cretaceous-Paleogene (K-Pg) extinction event is undoubtedly one of the most debated topics in the evolutionary history of life on the planet
Some of them are shared with the coeval fossil records of continental to transitional fossiliferous deposits [230,231], but others are specific to the Ibero-Armorican island
The vertebrate record of the Western Tremp Syncline comprises some of the youngest sedimentary deposits with vertebrate fossils in the late Maastrichtian of Europe, with a continuous succession from the upper part of chron C30r to chron C29r (≈67–66.052 Ma)

Summary

Introduction

The Cretaceous-Paleogene (K-Pg) extinction event is undoubtedly one of the most debated topics in the evolutionary history of life on the planet. At the end of the Cretaceous, a set of destabilizing events occurred on Earth, including a marine regression [2], climate changes [3,4], the volcanic activity of the Deccan Volcanic Province (India) with the emission of a huge amount of gases and volcanic material into the atmosphere [5,6,7,8], and the impact of an asteroid in Chicxulub (Mexico) 66 Ma ago [1,9,10,11,12] All these causes seem to have contributed to the extinction to a certain degree, the meteorite impact hypothesis shows the most solid arguments for having been the major disturbing mechanism [12,13,14,15,16]. Since the end of the 20th century, several research teams have worked on the uppermost Campanian–Danian outcrops in this area, improving our knowledge of the biodiversity of fossil vertebrates, the environments they inhabited, and the chronostratigraphic framework [31,33,34]

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