New eutherian mammals from the Late Cretaceous of Aix-en-Provence Basin, south-eastern France

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)

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.

Rapid morphological evolution in placental mammals post-dates the origin of the crown group

Resolving the timing and pattern of early placental mammal evolution has been confounded by conflict among divergence date estimates from interpretation of the fossil record and from molecular-clock dating studies. Despite both fossil occurrences and molecular sequences favouring a Cretaceous origin for Placentalia, no unambiguous Cretaceous placental mammal has been discovered. Investigating the differing patterns of evolution in morphological and molecular data reveals a possible explanation for this conflict. Here, we quantified the relationship between morphological and molecular rates of evolution. We show that, independent of divergence dates, morphological rates of evolution were slow relative to molecular evolution during the initial divergence of Placentalia, but substantially increased during the origination of the extant orders. The rapid radiation of placentals into a highly morphologically disparate Cenozoic fauna is thus not associated with the origin of Placentalia, but post-dates superordinal origins. These findings predict that early members of major placental groups may not be easily distinguishable from one another or from stem eutherians on the basis of skeleto-dental morphology. This result supports a Late Cretaceous origin of crown placentals with an ordinal-level adaptive radiation in the early Paleocene, with the high relative rate permitting rapid anatomical change without requiring unreasonably fast molecular evolutionary rates. The lack of definitive Cretaceous placental mammals may be a result of morphological similarity among stem and early crown eutherians, providing an avenue for reconciling the fossil record with molecular divergence estimates for Placentalia.

Evidence of Reproductive Stress in Titanosaurian Sauropods Triggered by an Increase in Ecological Competition

The occurrence of dinosaur pathologic eggs in the Late Cretaceous of Europe is well known, but their origin remains unclear. Here we expose the results of a detailed sampling of the conspicuous fossil record of Late Cretaceous titanosaurian eggs (oogenus Megaloolithius) from several southwestern Europe basins. After examining more than 450 samples, we observed a remarkable and statistically supported occurrence of multiple pathologic eggs in a relatively short stratigraphic range at the end of the early Maastrichtian, circa 71-70 Ma. All pathologic specimens exhibit multi-layered eggshell condition, a characteristic related to dystocia, or egg retention within the female uterus for an abnormal prolonged period of time. After exploring various scenarios, the occurrence of pathologic eggs is strongly correlated with an intense dinosaur faunal replacement that occurred during the early Maastrichtian in the Ibero-Armorican Island. Given that inter-species competiveness is proved to produce major affects in ecological communities, our results suggest that pathologies in the eggs of European titanosaurians could be a consequence of an increase in reproductive stress triggered by direct ecological competition between different dinosaurs. Thus, the present study provides a new perspective of how dinosaurs might have been affected by ecological/environmental disturbance.

Integrated Paleoenvironmental Reconstruction and Taphonomy of a Unique Upper Cretaceous Vertebrate-Bearing Locality (Velaux, Southeastern France)

The Velaux-La Bastide Neuve fossil-bearing site (Bouches-du-Rhône, France) has yielded a diverse vertebrate assemblage dominated by dinosaurs, including the titanosaur Atsinganosaurus velauciensis. We here provide a complete inventory of vertebrate fossils collected during two large-scale field campaigns. Numerous crocodilian teeth occur together with complete skulls. Pterosaur, hybodont shark and fish elements are also represented but uncommon. Magnetostratigraphic analyses associated with biostratigraphic data from dinosaur eggshell and charophytes suggest a Late Campanian age for the locality. Lithologic and taphonomic studies, associated with microfacies and palynofacies analyses, indicate a fluvial setting of moderate energy with broad floodplain. Palynomorphs are quite rare; only three taxa of pollen grains occur: a bisaccate taxon, a second form probably belonging to the Normapolles complex, and another tricolporate taxon. Despite the good state of preservation, these taxa are generally difficult to identify, since they are scarce and have a very minute size. Most of the vertebrate remains are well preserved and suggest transport of the carcasses over short distances before accumulation in channel and overbank facies, together with reworked Aptian grains of glauconite, followed by a rapid burial. The bones accumulated in three thin layers that differ by their depositional modes and their taphonomic histories. Numerous calcareous and iron oxides-rich paleosols developed on the floodplain, suggesting an alternating dry and humid climate in the region during the Late Campanian.

Island life in the Cretaceous - faunal composition, biogeography, evolution, and extinction of land-living vertebrates on the Late Cretaceous European archipelago

The Late Cretaceous was a time of tremendous global change, as the final stages of the Age of Dinosaurs were shaped by climate and sea level fluctuations and witness to marked paleogeographic and faunal changes, before the end-Cretaceous bolide impact. The terrestrial fossil record of Late Cretaceous Europe is becoming increasingly better understood, based largely on intensive fieldwork over the past two decades, promising new insights into latest Cretaceous faunal evolution. We review the terrestrial Late Cretaceous record from Europe and discuss its importance for understanding the paleogeography, ecology, evolution, and extinction of land-dwelling vertebrates. We review the major Late Cretaceous faunas from Austria, Hungary, France, Spain, Portugal, and Romania, as well as more fragmentary records from elsewhere in Europe. We discuss the paleogeographic background and history of assembly of these faunas, and argue that they are comprised of an endemic 'core' supplemented with various immigration waves. These faunas lived on an island archipelago, and we describe how this insular setting led to ecological peculiarities such as low diversity, a preponderance of primitive taxa, and marked changes in morphology (particularly body size dwarfing). We conclude by discussing the importance of the European record in understanding the end-Cretaceous extinction and show that there is no clear evidence that dinosaurs or other groups were undergoing long-term declines in Europe prior to the bolide impact.