Nannopterygius (meaning "small wing/flipper" in Greek) is an extinct genus of ophthalmosaurid ichthyosaur that lived during the Middle Jurassic to the Early Cretaceous (Callovian to Berriasian stages).

[4][better source needed] This gave it a very streamlined, torpedo-shaped look, but would have made it quite difficult to generate much lift or to turn quickly, making it an inefficient long-distance swimmer but speedy over short distances.

[9] It was home to a great variety of marine life, including many cephalopods, fishes such as Thrissops and the early ray Kimmerobatis, and remains of occasional dinosaurs like Dacentrurus which had been washed out to sea.

In addition, fossils of the pliosaurid Pliosaurus rossicus and indeterminate remains belonging to a metriorhynchid, as well as a high diversity of ammonites including the large-bodied taxon Titanites, are also known from the Volgian-aged sediments of this region.

[13] Despite this, near the top of the member, various diverse assemblages of invertebrates associated with cold seeps have been discovered; these include ammonites like Lytoceras and Phylloceras, lingulate brachiopods, bivalves like Myophorella and Laevitrigonia, rhynchonellate brachiopods, tubeworms, belemnoids, tusk shells, sponges like Peronidella, crinoids, sea urchins like Hemicidaris, brittle stars, starfish like Pentasteria, crustaceans like Eryma, and gastropods, numbering 54 taxa in total.

[14] 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.

[15] In addition to Nannopterygius, the Slottsmøya Member presents a diverse assemblage of other marine reptiles, including the ichthyosaurs Undorosaurus gorodischensis, several species belonging to the genus Arthropterygius, and a partial skull attributed to Brachypterygius sp.

[16][17][18][19] Additionally, 21 plesiosaurian specimens are also known from the site, including two belonging to the large pliosaur Pliosaurus funkei, three to Colymbosaurus svalbardensis, one to Djupedalia engeri, one to Ophthalmothule cryostea, and one each to Spitrasaurus wensaasi and S. larseni.