Rhynchosaurs were herbivores, and at times abundant (in some fossil localities accounting for 40 to 60% of specimens found), with stocky bodies and a powerful beak.

Rhynchosaur teeth had a unique condition known as ankylothecodonty, similar to the acrodonty of modern tuataras and some lizards but differing in the presence of deep roots.

These abundant animals might have died out suddenly at the end of the Carnian (Middle of the Late Triassic period), perhaps as a result of the extinction of the Dicroidium flora on which they may have fed.

All rhynchosaurs, apart from the four Early and Middle Triassic monospecific genera, Eohyosaurus, Mesosuchus, Howesia and Noteosuchus, are included in this family.

[8] However, Langer et al. (2000) noted that Hyperodapedontidae was erected by Lydekker to include Hyperodapedon gordoni and H. huxleyi, clearly excluding Rhynchosaurus articeps, which was the only other rhynchosaur known at that time.

Stenaulorhynchinae named by Kuhn (1933) is defined sensu Langer and Schultz (2000) to include all species more closely related to Stenaulorhynchus than to Hyperodapedon.

Hyperodapedontinae named by Chatterjee (1969) was redefined by Langer et al. (2000) to include "all rhynchosaurs closer to Hyperodapedon than to "Rhynchosaurus" spenceri" (now Fodonyx).