Paul Sereno and A. B. Arcucci named Crurotarsi in 1990, defining it as "Parasuchia [phytosaurs], Ornithosuchidae, Prestosuchus, Suchia, and all descendants of their common ancestor". The groups in this definition were considered crocodile-line archosaurs, as opposed to the bird-line archosaurs. Ornithosuchids were once considered bird-line archosaurs (as implied by their name, which means "bird crocodiles" in Greek), but were later recognized as crocodile-line archosaurs. This reclassification may have inspired Sereno's Crurotarsi, a node-based clade defined by the inclusion of ornithosuchids and other early archosaurs.
Two names were proposed for crocodile-line archosaurs before Crurotarsi was erected. The first, Pseudosuchia, was established as a stem-based clade in 1985. It includes crocodiles and all archosaurs more closely related to crocodiles than to birds. The second, Crocodylotarsi, was named in 1988, possibly as a replacement for Pseudosuchia. The name Pseudosuchia, meaning "false crocodiles", has been used for over a century, and traditionally included aetosaurs. As a clade, Pseudosuchia includes the group Eusuchia, or "true crocodiles". Crocodylotarsi may have been named to remove confusion, but as a stem-based clade it is synonymous with Pseudosuchia. Because Pseudosuchia was named first, it has precedence. Crurotarsi traditionally contains the same archosaurs as Pseudosuchia, but as a node-based clade it is not synonymous.
In 2011, Sterling J. Nesbitt found phytosaurs to be the sister taxon of Archosauria, and therefore not crocodile-line archosaurs. Because phytosaurs are included in the definition of Crurotarsi, this change in their phylogenetic placement expanded the scope of Crurotarsi, which therefore now includes phytosaurs, crocodiles, pterosaurs and dinosaurs. However, Pseudosuchia still contains only crocodile-line archosaurs.
Below is a cladogram modified from Nesbitt (2011) showing the new changes:
^ abcSereno, P.C.; Arcucci, A.B. (1990). "The monophyly of crurotarsal archosaurs and the origin of bird and crocodile ankle joints". Neues Jahrbuch für Geologie und Paläontologie Abhandlungen180: 21–52.
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