Poposauridae was coined by Nopcsa (1923) and initially thought by most to reside within Saurischia and possibly Theropoda. Steel (1970), for example, placed Poposauridae and its sole species Poposaurus gracilis in Carnosaria within Theropoda. Better specimens soon after linked Poposaurus and closest kin with crurotarsal archosaurs. Recent description and discovery of much more complete remains pertaining to Sillosuchus (Alcober and Parrish 1997) and Shuvosaurus (Nesbitt et al. 2005) will impact greatly on the understanding and placement of this clade within Suchia.
Parrish (1993:302) included four genera but did not define Poposuridae. The active definition is stem-based and uses the nominotypical Poposaurus gracilis as an internal specifier. Poposauridae, Paracrocodylomorpha and Crocodylomorpha form a conditional node-stem triplet.