Sereno et al. (2001) provided the first definition for Notosuchia, a clade that had been in common use, if ill-defined, in the literature. The active definition is a textual variant of that in Sereno et al. (2001). The definition uses Notosuchus terrestris as an internal specifier and eusuchian crocodilians as an external specifier.

Recently Carvalho et al. (2004) provided a second definition for Notosuchia; they did not cite the first definition and may have been unaware that it had been proposed. Their definition, in contrast, was not anchored on Notosuchus terrestris and does not use species as specifiers. Rather they employed higher level taxa as specifiers, which identified a considerably different clade. Their phylogeny does not include eusuchian crocodilians or other metasuchians, (e.g. Atoposauridae), so it is not clear whether they would be included by their definition. The original definition provided by Sereno et al. (2001) is clearer and follows more closely previous use in the literature.