Considered as the last survivors of a dying group, all Cretaceous ichthyosaurs have traditionally been incorporated within a single genus, Platypterygius. This waste-basket genus includes large ichthyosaurs with numerous, large and conical tooth crowns and bulbous polygonal root well anchored in dental grooves. With such a dentition, Platypterygius can be included within the “Smash guild”. However, the study of new specimens from the Aptian-Albian marls of the Vocontian basin (SE France) reveals an unexpected diversity of late Early Cretaceous ichthyosaurs. Beside “classical” Platypterygius specimens, another type of ichthyosaur with very tiny and pointed teeth has been found in the mid-Albian marls of Sisteron, in High-Provence Alps. This new taxon is based on a partial crushed skull, two basioccipitals, 8 teeth, and 15 centra. The teeth range from 20mm to 2cm and are highly compressed labio-lingualy, with a thickness/wideness ratio of the root sometimes as low as 1/4. Crowns are slightly curved and sharply pointed, indicating a diet of small and soft preys. Interestingly, although the rostral bones are slender and delicate – thus radically different from conventional Late Early Cretaceous ichthyosaurs – the basioccipital of this taxon shares many characters with Platypterygius and is of the same overall size. Together with the recently named genus Maiaspondylus from the Albian of western Canada, these specimens suggest a higher diversity of late Early Cretaceous ichthyosaurs, in contradiction with the current view of ichthyosaur extinction, said to be gradually decreasing in diversity since the Middle Jurassic. In fact, the number of ecological niches occupied by ichthyosaurs apparently even increased from the Late Jurassic until the late Early Cretaceous. Therefore, the ecological impact of the Cenomanian-Turonian boundary on marine reptile faunas was probably more severe than previously thought. |
