The elasmobranchii from the Palaeocene-Eocene transition at Dormaal (Belgium): biostratigraphical and palaeobiogeographical implications

The Dormaal elasmobranch fauna, which is believed to be the most diverse of the European Palaeocene (46 taxa), is very similar to that of the Ressons Sands of the Paris Basin (name introduced by Steurbaut ei ai. to specify the upper part of the Bracheux Sands) and that of the Paspotansa Member of Chesapeake Bay (Aquia Formation. USA), both dated as late Palaeocene and located within Biochron NP9. This reworked fauna suggests that the Bois-Gilles Sand Formation, lateral equivalent of the Rc suns Sands. was deposited at the Dormaal site, bur subsequently completely eroded during the incision of the Dormaal palaeovalley. The Dormaal assemblage is dominated by rather large sharks, indicating warm, shallow marine habitats with normal salinity and sandy sea-bottoms. The evolutionary history of the European shallow water elasmobranchii is marked by a series of events, of which three are major. The Dormaal association represents the third diversification event, dated as late Thanetian. It is characterised by the entry in the southern North Sea of the first devil-rays (Mobulidae), by the appearance of butterfly-rays (Gymnura) and of several small orectolobiforms. up to now considered to be of Ypresian age.