than the rest of the bone. Also uniquely among ophthalmosaurids, this fused element is shorter than the femur. Both ends of the femur of Arthropterygius are approximately the same width, with the middle of the femoral shaft being slightly narrower. The top end was slightly thicker than the rest of the bone along its front rim. Unlike Ophthalmosaurus, the femoral dorsal and ventral processes were rather reduced. At the bottom end, there are two facets, one for the tibia and one for the fibula; this is typical of ophthalmosaurids, but Platypterygius hercynicus, Platypterygius americanus, Platypterygius australis, and Nannopterygius all have three. Both facets in Arthropterygius were roughly the same length, and the fibular facet was directed slightly to the back, forming an angle of 120° with the tibial facet. Discovery and classification The genus was first named in 2010 by Erin E. Maxwell as the generic replacement name for Ophthalmosaurus chrisorum, which was named in 1993 from fossils found on Melville Island in the Northwest Territories. Its fossils are the most complete of any ichthyosaur in the Canadian Arctic. A. chrisorum has several features that separate it from the genus Ophthalmosaurus, including a highly angled articulation between the radius and ulna and the humerus. Maxwell 2010 found it to be the sister taxon of Caypullisaurus, an ophthalmosaurid from Argentina. However, many recent cladistic analyses found it to be the basalmost member of the Ophthalmosauridae. In 2012, a skull and forefin discovered of an ophthalmosaurid ichthyosaur discovered in the Neuquén Basin of Argentina were described. This specimen was notable for presenting unusual braincase morphology including the opening for the internal carotid artery on the posterior surface of the parabasisphenoid, which is a diagnostic trait of Arthropterygius, which was at the time only known from Canada. This specimen was initially referred to Arthropterygius sp., massively expanding the known range of the genus. This presents strong evidence that some Jurassic marine reptiles had near cosmopolitan distributions, much like many marine mammals today. A paper published by Campos et al. in 2019 further describes this specimen, and designates it as the holotype of a new species, A. thalassonotus. Eight seasons of excavations led by the Spitsbergen Mesozoic Research Group on the island of Spitsbergen, Svalbard, Norway from 2004 to 2012 recovered 29 ichthyosaur specimens from outcrops of the Slottsmøya Member lagerstätte, which belongs to the greater Agardhfjellet Formation. These outcrops likely date to the