Atoposauridae has been placed within Mesosuchia (Romer 1956, Steel 1973) or Metasuchia (Clark 1994, Sereno et al. 2001) and has included a number of genera such as Alligatorellus, Alligatoriuim, Atoposaurus, and Theriosuchus. Recently the younger Albian-age Pachycheilosuchus trinquei was described as a close relative to known atoposaurids (Rogers 2003).

The active and first definition of Atoposauridae is stem-based. It anchors the definition on the nominotypical species Atoposaurus beaumonti and would include Pachycheilosuchus trinquei as long as it remains more closely related to the former than to another crocodyliform clade.