Arthropterygius thalassonotus was named by Campos et al. (2020) [Arthropterygius thalassonotus differs from the type species Ar. chrisorum in the following features: 1. In posterior view, the ventral edge of the basisphenoid is convex (whereas in Ar. chrisorum this area is almost flat). 2. In ventral view, the basisphenoid in Ar. thalassonotus is quadrangular in shape (pentagonal in Ar. chrisorum). 3. The basipterygoid processes are anterolaterally directed (laterally oriented in Ar. chrisorum). 4. The radius and ulna are markedly ovate (they present straight edges in Ar. chrisorum). 5. The intermedium is ovate (whereas in Ar. chrisorum it is diamond shaped).]. Its type specimen is MOZ-PV 6145, a partial skeleton (a partial skeleton consisting of a skull lacking the anterior portion of the rostrum and a partly articulated right forefin), and it is a 3D body fossil. Its type locality is Yesera del Tromen–Pampa Tril, which is in a Tithonian marine horizon in the Vaca Muerta Formation of Argentina.