Crurotarsi

Crurotarsi is a clade within Archosauriformes that comprises the crocodile-line archosaurs and their extinct relatives. The name derives from the crurotarsal ankle joint, a distinctive hinge-like connection between the tarsal bones and the tibia found in many members of the group. This ankle morphology helps distinguish crocodile-line archosaurs from the bird-line archosaurs of Avemetatarsalia.

Composition and members: The group traditionally includes the pseudosuchians, the crocodile-line archosaurs, and a variety of Triassic outgroups such as phytosaurs, aetosaurs, and rauisuchians. The only living representatives are crocodylians (crocodiles, alligators, caimans) and their close relatives.

Evolution and fossils: Crurotarsi originated near the end of the Permian or in the early Triassic and diversified throughout the Triassic, occupying a wide range of ecological roles from terrestrial predators to armored herbivores. Although many Triassic lineages went extinct, the crocodilian lineage endured and remains the sole living branch of Crurotarsi today.

Taxonomic notes: The exact composition of Crurotarsi has varied with phylogenetic analyses, and some groups have been reassessed within archosaur relationships. In modern classifications, Crurotarsi is distinguished from Avemetatarsalia, the bird-line archosaurs, highlighting the major split among archosaurs.