Taphonomy of Saint-Vallier (Drôme, France), the reference locality for the biozone MN17 (Upper Pliocene)

Saint-Vallier (Drôme, France) is the biostratigraphical reference locality for the biozone MN17 (Upper Pliocene, between 2.4 and 1.9  Ma). The taphonomic study presented here is based on the results of a recent 6-year campaign of renewed study. Carefully controlled excavations allow the study of the relative position of remains and their orientation inside several fossil clusters. Flowing water is the most likely agent responsible for fossil orientation: bones of the animals were carried by water from distal to proximal areas of deposition, where they were quickly buried by sediments. Taphonomic clues suggest that the causes of mortality were attritional. The study of mortality profiles yields more ambiguous results although not necessarily in contrast with the attritional hypothesis. Such a study shows the importance of the sample size for the interpretation of the age diagrams.