Les Nautiles du Jurassique d'Arabie saoudite

Abstract

Between the numerous fossils coming from jurassicoutcrops of Saoudian Arabia, Nautiloids play an important role. One hundred of specimens, going from Upper Lias to Kimmeridgian, were sampled in the whole of formations. Their taxonomic study, constituing the main part of this work, bring to recognition of 34 species, of which 7 are new, distributed in 7 genera, of which one ( Aulacenoceras) is new. Most of those species display a very restricted vertical distribution and have therefore a very significant biostratigraphical value, leading to the same results as other groups, specially Ammonoids. But exact comparison with classical european faunas are difficult, because of inadequate knowledge of those, and strong endemism of saoudian fauna. From evolutive point of view, it is interesting to note the persistence to Callovian stage of the genus Metacenoceras, the early appearance, in the Upper Bajocian, of the genus Paracenoceras, with very varied lineage going to Kimmeridgian. From ecological point of view, the completeabsence of forms with strongly folded sutures ( Pseudaganides), rarety of costed species and frequency of species with new numerous septa point to a very shallow and calm environment.