The widely spaced peg-like teeth project at the front of the jaws, indicating that these animals fed on fish.

In the species Prosantosaurus, it was observed that they fed on small fishes and crustaceans which they devoured entirely and that its teeth regrew after they broke off.

In some more recent cladistic classifications, however, (Rieppel 2000), they are considered the sister group to the Eosauropterygia, the clade that also includes the nothosaurs and pistosauroids.

[3] In the 2023 description of Luopingosaurus, Xu et al. supported a similar hypothesis, recovering Pachypleurosauroidea as the sister taxon to the Eusauropterygia.

The results of their phylogenetic analyses are shown in the cladogram below:[5] Placodontia Hanosaurus Majiashanosaurus Diandongosaurus Dianmeisaurus Dawazisaurus Panzhousaurus Dianopachysaurus Keichousaurus Dactylosaurus Anarosaurus Odoiporosaurus Serpianosaurus Neusticosaurus Prosantosaurus Qianxisaurus Wumengosaurus Luopingosaurus Honghesaurus Nothosauroidea Pistosauroidea