Avemetatarsalia

Avemetatarsalia (meaning "bird metatarsals") is a clade name established by British palaeontologist Michael Benton in 1999 for all avesuchians (crown group archosaurs) that are closer to dinosaurs than to crocodiles.

An improved description of the small archosaur Scleromochlus together with a cladistic analysis of its phylogenetic position demonstrated that Scleromochlus was more closely related to the dinosaurs than to the Crurotarsi (to which the crocodiles belong) but outside of the node-based clade Ornithodira as originally interpreted by Jacques Gauthier: the group containing the last common ancestor of the dinosaurs and the pterosaurs and all of its descendants.

Paul Sereno had in 1991 given a formal (and different) definition of Ornithodira, one in which Scleromochlus was explicitly added. However, at that point, there was no named clade that could encompass species with a basal position on the archosaurian branch leading to dinosaurs (as opposed to that leading to crocodiles) so Benton named a new branch-based clade for this purpose: Avemetatarsalia, named after the birds (Aves), the last surviving members of the clade, and the metatarsal ankle joint that was a typical character of the group. Avemetatarsalia was defined as: all Avesuchia closer to Dinosauria than to Crocodylia.