The term "nothosaur" has been variously employed over the years. Originally it was used to describe a group of plesiomorphic ('primitive') Sauropterygia, a group subsequently recognised as paraphyletic (including many different groups) (Storrs, 1993), thus making the term redundant. This group contained what are now known as the monophyletic pachypleurosauroidea and all other members of the redundant clade were referred to as "nothosaurs". The name Nothosauria has been reinstated recently (Rieppel, 2000, 2002) to encompass a monophyletic suite of basal sauropterygians including Germanosaurus, Nothosaurus and Lariosaurus, but excluding Simosaurus.

\--------Nothosauroidea------------ \ \ \--------Cymatosauridae---------- \----Pistosaurus and Augustasaurus \---- Plesiosauria

-----Simosauria---------------------- \----Nothosauria---------------------   \----Corosaurus \----Cymatosaurus

---------Simosauridae--------- ---------Nothosauridae-------- \ \Germanosauridae \---Germanosaurus

-----Simosaurus \ \----Lariosaurus \----Nothosaurus \----Paranothosaurus