Parvipelvia is a major clade of ichthyosaurians that diversified during the Triassic-Jurassic transition. The interrelationships of early parvipelvians remain unclear and many genera are loosely diagnosed, such as Temnodontosaurus, an ecologically important genus from the Early Jurassic of Western Europe. One taxon concentrates many taxonomic issues: ‘Ichthyosaurus’ acutirostris was previously assigned to Temnodontosaurus and for which ‘Ichthyosaurus’ zetlandicus represents a junior synonym. We redescribe the holotype of ‘Ichthyosaurus’ zetlandicus (CAMSM J35176) and a new specimen probably attributable to this taxon (MNHNL TU885) from the Toarcian of Luxembourg. We find that Temnodontosaurus zetlandicus comb. nov. is a valid species that should be referred to the genus Temnodontosaurus, sharing a number of traits with Temnodontosaurus nuertingensis and Temnodontosaurus trigonodon, despite having a distinct cranial architecture. Our phylogenetic analyses under both implied weighting maximum parsimony and Bayesian inference recover T. zetlandicus as closely related to several species currently assigned to Temnodontosaurus. Species included in Temnodontosaurus form a polyphyletic yet well-clustered group among basal neoichthyosaurians, demonstrating that the monophyly of this genus needs to be thoroughly investigated.

Despite abundant fossils, the quality of the fossil record of Early Jurassic marine reptiles strongly fluctuates with time and space. Pliensbachian strata have yielded very few marine reptile remains, especially outside of England, obscuring the evolution of marine reptiles during the middle part of the Early Jurassic. We report a new Pliensbachian locality from Luxembourg that contains abundant marine fauna and ichthyosaurian remains likely representing a single individual, composed of a partial snout, a possible surangular, two centra, and several ribs and gastralia. Ammonites and belemnites place this locality within the Valdani-Luridum Ammonite subzones of the Ibex Ammonite Zone, lower Pliensbachian. We assign the new ichthyosaur specimen to the clade Leptonectidae, using a combination of features from the snout and teeth. This specimen indicates that large neoichthyosaurians were present in multiple places of the European archipelago in all stages of the Early Jurassic and suggests that the ichthyosaurian faunae of western Europe remained essentially similar across the Sinemurian-Pliensbachian interval.

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