Alexeyisaurus
Humerus of Alexeyisaurus holotype (SGU 104a/36)
Alexeyisaurus is the stratigraphically oldest named possible plesiosaur. It was named and described by Sennikov and Arkhangelsky (2010) as an elasmosaurid plesiosaur from the Late Triassic of Franz Josef Land, Russia. This would be highly unusual because the oldest definitive elasmosaurid plesiosaurs are otherwise restricted to the Cretaceous Period. The holotype material of…
Abyssosaurus
Abyssosaurus is a derived cryptoclidid plesiosaur from the Upper Hauterivian (Lower Cretaceous) of the Menya River, Chuvashia, Russia. It was named and described in 2011 by Alexander Yu Berezin (Berezin 2011). A partial skull associated with the holotype specimen (MChEIO no. PM/1) was not described in the original 2011 paper but was…