First Mosasauridae (Reptilia, Squamata) in the Late Campanian (latest Cretaceous) of Savoie (Chartreuse Massif, French Alps).
Résumé
Mosasaurid were a very successful clade of marine squamates, highly systematically and ecologically diversified and worldwidely widespread, known from the Cenomanian to the end of the Maastrichtian where they disappear during the K/Pg biological crisis. Mosasaurids are known from complete skeletons in several outcrops in the world like the extensive ones of the WIS of North America, Morocco, Belgium, the Netherlands, and New Zealand. The fossil record of mosasaurids is comparatively rather poor in France, and most discoveries dated from the end of the XIXth century. Here we report on the first discovery of mosasaurid remains in the Late Cretaceous of the subalpine massif of Chartreuse, a mountainous region of the Alps, a hundred kilometers southwest of the Mont-Blanc massif. The specimen has been found by one of us (FD) during a walk in a forest located in the Chartreuse Regional Nature Park near the village of Entremont-le-Vieux, not far from Chambéry, in Savoie. The remains were found in a marly grey chalk deposited in the ”dauphinois domain” of the Tethys Ocean. It is very rich in invertebrates remains, including mainly molluscs like Cephalopods (Ammonites, Belemnites, Nautiles), Bivalves and Gastropods, as well as Echinoids, Brachiopods and possibly Arthropods. Microvertebrate remains (fish teeth) have also been found, as well as possible plant ones. The ammonites found there, like Nostoceras polyplocum indicate a Late Campanian age for the outcrop.
The mosasaurid remains consist of around twenty caudal vertebrae found articulated. Though generally well preserved, they are slightly laterally compressed. The vertebrae include only the centra and part of the fused haemal arches in some of them. The centra are slighly procoelous and vertically oval in shape. Most are about 3 cm high and long, the smallest ones being half this size. The fact that these centra preserved both transversal processes and haemal arches indicatedthat they correspond to median caudals, located probably anterior to the caudal flexure. The fact that the haemal arches are fused to the centra also indicate that this specimen belong to the Mosasaurinae clade. In Europe, only Mosasaurus and Prognathodon have been already found. Only the detailed description of this new specimen would permit to precise its systematical attribution. This new discovery permits to improve the rather poor French mosasaurid fossil record. It represents the first discovery of mosasaurid remains in the Alps.