Classification
Plesiosaurian clades
This nested classification for Plesiosauria shows the major clades (groups). Note that some classifications have placed Rhomaleosauridae outside of Pliosauroidea (=pliosaurs) but I have used a traditional approach here and nested Rhomaleosauridae within pliosauroids.
Sauropterygian clades
Plesiosaurs (=Plesiosauria) are derived sauropterygians. This nested classification of Sauropterygia shows the position of Plesiosauria relative to other major sauropterygian clades.
Redundant sauropterygian clades
‘Nothosauriformes’
‘Cimoliasauridae’