Nannopterygius

Nannopterygius (meaning "small wing/flipper" in Greek) is an extinct genus of ophthalmosaurid ichthyosaur that lived in the Middle Jurassic to the Early Cretaceous (Callovian to Berriasian stages). Fossils are known from England, Russia, and Norway.
Description.
"Nannopterygius" was small for an ichthyosaur, at only long. About of this was tail, including a deeply forked and probably homocercal caudal fin. The head is long, with a typical long narrow rostrum. The eyes are large, hence its classification as an ophthalmosaurid, and have a bony sclerotic ring inside the eye socket. There are at least 60 disc-shaped vertebrae, although owing to the condition of the fossil it is not possible to tell exactly how many there were, showing that "Nannopterygius" was flexible, agile and probably a fast swimmer. The ribs are long and curved, but do not quite join up. Most of the features are very similar to the close relative "Ophthalmosaurus." However, its paddles are much smaller, around for the forepaddles and only for the hindpaddles. 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. It is therefore possible that it was an ambush predator which plunged into shoals of fish quickly in the shallow seas where it lived.
Discovery and Classification.
The first specimen was found in the Kimmeridgian Kimmeridge Clay Formation of Kimmeridge Bay, Dorset, UK and described by Hulke in 1871, who named it "Ichthyosaurus enthekiodon". This referred to its teeth being 'sheathed' in cementum and less likely to fall out than those of other ichthyosaurs. A year earlier, Hulke had described some remains from the same horizon and locality that he thought were ichthyosaurian, naming them "Enthekiodon" (no species given). These are now lost, but Hulke considered them sufficiently similar to demote the name to species level. In 1922, Friedrich von Huene separated this species into the new genus "Nannopterygius", named for the small fore- and hindpaddles. The first fossil is the most complete, but is flattened. All subsequent fossils are fragmentary. In 2020, several more species, including "N. borealis", and the species once contained in the genera "Paraophthalmosaurus" and "Yasykovia" were named based on remains found in Norway and Russia.
The following cladogram shows a possible phylogenetic position of "Nannopterygius" in Ophthalmosauria according to an analysis performed by Zverkov and Jacobs (2020).
Paleoecology.
The type species is known from the Kimmeridge Clay Formation in Dorset, England. The Kimmeridge Clay hosts a wealth of marine fossils dating to the Kimmeridgian and Tithonian stages of the Late Jurassic, many of which are incredibly well preserved, however unfortunately very little has been published. At the time, Europe represented an island archipelago which was closer to the equator than it is today, surrounded by warm, tropical seas. The Kimmeridge Clay specifically represents an offshore marine environment, in which the seafloor was far enough below the surface not to be disturbed by storms. 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. It is most famous for diversity of marine reptiles, such as the metriorhynchids "Metriorhynchus" and "Plesiosuchus", the plesiosaurs "Colymbosaurus" and "Kimmerosaurus", and the ichthyosaurs "Grendelius" and "Thalassodraco". The apex predators of the Kimmeridge ecosystem would have been the several species of the pliosaurid "Pliosaurus" which have been recovered there, as well as large metriorhynchids like "Plesiosuchus". Additionally, the pterosaurs "Cuspicephalus" and "Rhamphorhynchus" are also known from the Kimmeridge Clay.
The species "N. yasykovi" and "N. saveljeviensis" are known from the Volga region of Russia, which gives the Volgian stage its name. Though very little is known or published about the fossils of these localities, fossils of a number of marine animals have been recovered, including several species of the ichthyosaurs "Arthropterygius", "Grendelius", and "Undorosaurus". In addition, fossils of the pliosaurid "Pliosaurus rossicus" and indeteminate 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. There is also evidence for the presence of sea ice and glaciers from deposits in eastern Europe and the Volga region of Russia.
Additionally, the species "N. borealis" is known from earliest Cretaceous sediments of the Slottsmøya Member of the Agardhfjellet Formation. The Slottsmøya Member consists of a mix of shales and siltstones and was deposited in a shallow water methane seep environment. 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. 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, as in the Volga. 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." The presence of these taxa indicates that there was significant faunal exchange across the seas of Northern Europe during this time period. 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". Many of these specimens are preserved in three dimensions and partially in articulation; this is correlated with high abundance of organic elements in the sediments they were buried in.