Multiproxy palaeoenvironmental reconstruction of the Bathonian Castelbouc sauropod tracksite (Causses Basin, southern France): insight into a Middle Jurassic insular ecosystem

Jean-David Moreau (1) , Vincent Trincal (2) , Benjamin Bourel (3) , Marc Philippe (1) , Romain Vullo (4) , Alain Jacquet (5, 6) , Christophe Durlet (1) , Marie-Béatrice Forel (7) , Didier Néraudeau (4) , Sylvain Charbonnier (7) , Dahvya Belkacem (3)

1 BGS - Biogéosciences [UMR 6282]
2 LMDC - Laboratoire Matériaux et Durabilité des constructions
3 IMBE - Institut méditerranéen de biodiversité et d'écologie marine et continentale
4 GR - Géosciences Rennes
5 Association Paléontologique des Hauts Plateaux du Languedoc
6 Lycée Emile Peytavin
7 CR2P - Centre de Recherche en Paléontologie - Paris

We report lignitic fossil rich-beds from the Bathonian Castelbouc sauropod tracksite (Castelbouc Cave N°4, Causses Basin, southern France). Showing the co-occurrence of amber with plant, vertebrate and invertebrate remains, they are a precious tool to reconstruct Middle Jurassic dinosaur ecosystems. A multiproxy approach combining sedimentology, petrology, mineralogy and palaeontology led to determine that these fossil rich-beds were deposited in a range of insular coastal palaeoenvironments. They include protected backshore areas such as freshwater/brackish ponds and brackish bay/lagoon showing co-occurrence of terrestrial and marine inputs. The backshore environments were particularly rich in ostracods (Darwinula sp., Fabanella bathonica) and gyrogonites of charophytes (Porochara douzensis). The abundance of conifer remains including leafy axes (Brachyphyllum), cones (cf. Classostrobus), wood (Brachyoxylon) and pollen grains (Classopollis) shows that ponds and bay/lagoon were bordered by conifer-dominated forests in which Cheirolepidiaceae were the main component. Such a rich and relatively diverse flora was probably an attractive source of food for megaherbivorous dinosaurs. Vertebrate microremains mostly consist of fish scales (Ginglymodi indet.) and crocodylomorph teeth (Atoposauridae indet.), two groups that are common components of Middle Jurassic paralic faunas. The palaeobotanical assemblage suggests a warm subtropical climate probably tropophilous with marked alternation between a wet and a dry season.

Mots clés: Amber; Conifers; Vertebrate microremains; Ostracods; Palaeoecosystem; Central Massif

Domaines: Paléontologie; Stratigraphie

Jean-David Moreau, Vincent Trincal, Benjamin Bourel, Marc Philippe, Romain Vullo, et al.. Multiproxy palaeoenvironmental reconstruction of the Bathonian Castelbouc sauropod tracksite (Causses Basin, southern France): insight into a Middle Jurassic insular ecosystem. Geobios, In press, ⟨10.1016/j.geobios.2023.12.007⟩. ⟨insu-04565562⟩