the Late Jurassic. They also recognize the previously dubious taxon "Ichthyosaurus" volgensis from Syzran in Russia as belonging to a newly recognized species of Arthropterygius, A. volgensis. This provides further support for the previously established idea that there was significant faunal interchange between the Volga region and Svalbard during the Volgian. While Zverkov and some others treat Janusaurus, Keilhauia and Palvennia within Arthropterygius, a study on the Jurassic Ichthyosaurs performed by Delsett et al. suggests the synonymy is not supported by the presence evidence. Phylogeny The following cladogram shows a possible phylogenetic position of Arthropterygius in Ophthalmosauridae according to the analysis performed by Zverkov and Jacobs (2020). Paleoecology Arthropterygius appears to have been a particularly wide ranging genus, with fossils known from several high latitude localities across the Northern Hemisphere, as well as an isolated specimen from Argentina. The Slottsmøya Member of the Agardhfjellet Formation, from which fossils of A. chrisorum, A. lundi, and A. hoybergeti have been recovered, provides perhaps the best glimpse into the ecosystems and habitats this genus was a part of. It consists of a mix of shales and siltstones and was deposited in a shallow water methane seep environment, near a patch of deeper marine sediment. The seafloor, which was located about below the surface, seems to have been relatively dysoxic, or oxygen-poor, although it was periodically oxygenated by clastic sediments. Despite this, near the top of the member, various diverse assemblages of invertebrates associated with cold seeps have been discovered; these include ammonites, lingulate brachiopods, bivalves, rhynchonellate brachiopods, tubeworms, belemnoids, tusk shells, sponges, crinoids, sea urchins, brittle stars, starfish, crustaceans, and gastropods, numbering 54 taxa in total. Outside of the cold seeps, many of these invertebrates were also present in abundance. Though direct evidence from Slottsmøya is currently lacking, the high latitude of this site and relatively cool global climate of the Tithonian mean that sea ice was likely present at least in the winter. In addition to Arthropterygius, the Slottsmøya Member presents a diverse assemblage of other marine reptiles, including the ichthyosaurs Undorosaurus gorodischensis, Nannopterygius borealis, and a partial skull attributed to Brachypterygius sp.. Additionally, 21 plesiosaurian specimens are also known from the site, including two belonging to the large pliosaurid Pliosaurus funkei, which would have been the apex predator of the ecosystem, three to Colymbosaurus svalbardensis, one to Djupedalia engeri, one to Ophthalmothule cryostea, and one each to Spitrasaurus wensaasi and S.