The original intention in defining Crurotarsi was to coin a “stem-based taxon” in place of Pseudosuchia (Sereno 1991:42). The active definition is a second-order revision, because the original definition (Sereno and Arcucci 1990:41) and that in Sereno (1991:27) were node-based in error. As defined here, Crocodylotarsi and Pseudosuchia are potentially synonomous with Crurotarsi. Given the “Pan-” prefix suggested recently as a convention (Joyce et al. 2004), there may eventually be an additional junior synonym (“Pancrocodylia”).
Preference is given to Crurotarsi over Pseudosuchia (or Crocodylotarsi) despite the earlier date of definition of the latter, because of the long historical association of Pseudosuchia (“false crocodiles”) with polyphyletic taxonomic content that excluded crocodylomorphs as well as phytosaurs. In Krebs’ (1976) review, Pseudosuchia includes archosaur outgroups (Euparkeria) and taxa closer to birds (Scleromochlus) but excludes crocodylomorphs and phytosaurs. Abandoning Pseudosuchia for a more recently coined and defined taxon Crurotarsi is done reluctantly. Factors that enter such a decision include the mportance of past use regarding Pseudosuchia as well as the etymology of both taxa. Although taxa such as Dinosauria have successfully accommodated a living crown clade (Aves) that was once excluded, the name of the taxon at hand was not “Pseudoaves” and was not erected specifically for non-birds.
Crocodylotarsi, coined two years prior to Crurotarsi but first defined two years later, would have been another possibility. However, it has been defined as a less inclusive, node-based clade linked to the “crocodile normal” tarsus. Basal relationships within Crurotarsi are not well established, and so a taxon so defined may well prove redundant. Recently Parrish (1997) has abandoned Crocodylotarsi and Crurotarsi, whereas other authors have adopted Crurotarsi (Juu, 1994, Brochu 2001).