Originally described by Wagner (1853) as Ichthyosaurus leptospondylus, it has had an unstable taxonomic history.
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It has also been named Ichthyosaurus trigonus posthumus, and identified with Macropterygius and Brachypterygius extremus.
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In addition to its late Jurassic occurrence, Aegirosaurus has recently been discovered from the late Valanginian (Early Cretaceous) of Southeastern France (Laux-Montaux, department of Drôme; Vocontian Basin), the first diagnostic ichthyosaur recorded from the Valanginian.