Aristonectes
Aristonectes (meaning 'best swimmer') is an extinct genus of plesiosaur from the Late Cretaceous Paso del Sapo Formation of what is now Argentina, the Quiriquina Formation of Chile and the Lopez de Bertodano Formation of Antarctica. The type species is Aristonectes parvidens, first named by Cabrera in 1941.
Aristonectes quiriquinensis was a large plesiosaur, with the holotype measuring over 10 metres (33 ft) long and weighing 4 metric tons (4.4 short tons).[1][2] A rough estimate based on the specimen from the Lopez de Bertodano Formation (identified as cf. Aristonectes sp.) indicates that Aristonectes was one of the largest plesiosaurs ever to exist, with an estimated body length of 11–11.9 metres (36–39 ft) and an estimated body mass of 10.7–13.5 metric tons (11.8–14.9 short tons).[3][a]
Aristonectes was classified variously since its original 1941 description, but a 2003 review of plesiosaurs from Patagonia conducted by Gasparini et al. (2003) found that Aristonectes was most closely related to elasmosaurid plesiosaurs like Elasmosaurus. The authors also considered Morturneria a junior synonym of Aristonectes because the former's holotype has unfused neural arches of the vertebrae indicative of juvenile status.[4] Subsequent study, however, revalidated Morturneria based on non-ontogenetic differences from Aristonectes.[5]
Aristonectes was placed within its own family, Aristonectidae, along with Tatenectes, Kaiwhekea, and Kimmerosaurus, by O'Keefe and Street (2009), as sister family of the polycotylid cryptoclidoids. However, subsequent studies (Otero et al., 2014)[6][7] returned Aristonectes to Elasmosauridae, recovering the genus as a derived elasmosaurid and therefore relegating Aristonectidae to a subfamily of Elasmosauridae, as Aristonectinae.
