An Early Cretaceous ichthyosaur from SE France: implications on the evolution of post-Liassic Ichthyosauria

A complete ichthyosaur rostrum with 124 associated teeth was recently discovered in Laux-Montaux locality, department of Drôme, southeastern France. The associated belemnites and ammonites indicate a late Valanginian age (Neocomites peregrinus Zone, Olcostephanus nicklesi Subzone) for this fossil, which consequently represents the first diagnostic ichthyosaur ever reported from Valanginian strata. Despite its incompleteness, this specimen is perfectly consistent with Aegirosaurus leptospondylus WAGNER 1853 and is therefore referred to this rare taxon. This specimen thus greatly increases the temporal and geographic biozones of this taxon, which was previously restricted to the Tithonian (Upper Jurassic) lithographic limestones of Bavaria (southern Germany). Moreover, it indicates that Late Jurassic ichthyosaurs actually crossed the Jurassic-Cretaceous boundary with a much lighter diversity drop than previously supposed. Finally, tooth morphology and wear pattern suggest that Aegirosaurus belonged to the “Pierce II/ Generalist” feeding guild sensu Massare (1987; 1997), which was hitherto not represented in post-Liassic ichthyosaurs.