GENUS ARTHROPTERYGIUS MAXWELL, 2010 Type species: Arthropterygius chrisorum (Russell, 1993) Maxwell, 2010. Amended diagnosis: Ophthalmosaurid ichthyosaur characterized by the following unique combination of characters: basioccipital facet equal or wider than dorsal plateau of basisphenoid; short basipterygoid processes giving to basisphenoid a square outline in dorsal view [as in Gengasaurus (Paparella et al., 2016), Ichthyosaurus communis De la Beche & Conybeare, 1 8 2 2, Maiaspondylus (Maxwell & Caldwell, 2006), Stenopterygius quadriscissus (Quenstedt, 1856), Sveltonectes (Fischer et al., 2011) and Temnodontosaurus (Lydekker, 1889)]; internal carotid foramen piercing basioccipital facet of basioccipital [shared only with Palvennia (Druckenmiller et al., 2012)]; humerus with a posteriorly deflected ulnar facet [as in Acamptonectes (Fischer et al., 2012), Baptanodon natans (Marsh, 1879), Janusaurus (Roberts et al., 2014), Ophthalmosaurus icenicus Seeley, 1874 and Undorosaurus gorodischensis Efimov, 1999]; strong dorsoventral compression of posterior half of humerus (shared with Janusaurus and Keilhauia (Delsett et al., 2017)]; reduced deltopectoral crest (as in Janusaurus) and humeral torsion poorly developed. ARTHROPTERYGIUS THALASSONOTUS CAMPOS,

Published as part of Campos, Lisandro, Fernández, Marta S. & Herrera, Yanina, 2020, A new ichthyosaur from the Late Jurassic of north- west Patagonia (Argentina) and its significance for the evolution of the narial complex of the ophthalmosaurids, pp. 180-201 in Zoological Journal of the Linnean Society 188 on page 184, DOI: 10.1093/zoolinnean/zlz095, http://zenodo.org/record/5719099