Sauropterygia–> Eosauropterygia–> Pachypleurosauria
The Pachypleurosauria is an exclusively Middle Triassic-aged group of semi-aquatic sauropterygians. They were once regarded as a type of ‘nothosaur’, but the traditional concept of “Nothosauria” is no longer in use because it was a paraphyletic group containing two separate evolutionary lineages. The more ‘primitive’ of the two is the Pachypleurosauria, while the more derived members form a separate clade called the “Nothosauria” under a revised definition (Rieppel, 1998).
Pachypleurosaur genera include: