When the "primitive" shark Tribodus (Hybodontiformes) meets the "modern" ray Pseudohypolophus (Rajiformes): the unique co-occurrence of these two durophagous Cretaceous selachians in Charentes (SW France)
Résumé
The palaeoecology and palaeobiogeography of two Cretaceous selachian genera, Tribodus BRITO & FERREIRA, 1989 and Pseudohypolophus CAPPETTA & CASE, 1975, are briefly discussed. These two similar-sized taxa developed an analogous pavement-like grinding dentition, characterized by massive teeth with a rhomboidal to hexagonal occlusal surface.Although both genera appear to have been euryhaline forms, the hybodont Tribodus occurred in fresh/brackish water habitats (e.g. deltas) to shallow marine lagoons, whereas the ray Pseudohypolophus lived in brackish water to coastal marine environments. Palaeobiogeographically, their global distribution displays two distinct but adjoined areas, with Tribodus being present in the northern part of Gondwana (Brazil and NorthAfrica), and Pseudohypolophus occurring on both sides of the NorthAtlantic (NorthAmerica andWestern Europe). However, the two genera coexisted during Cenomanian times within a small overlap zone, localized in western France. A trophic competition may have arisen from this situation between these two selachians belonging to the same trophic guild. This peculiar situation is well documented within the Cenomanian transgressive series of Charentes (SWFrance), where a turnover between the two forms is observed (replacement of Tribodus by Pseudohypolophus).