pseudosuchians

Pseudosuchia is a major clade within Archosauria that comprises the crocodile line and its extinct relatives. In modern classifications, pseudosuchians are the archosaurs more closely related to crocodilians than to birds and pterosaurs, which belong to the sister group Ornithodira. The split between the crocodile line and the bird line occurred at the base of Archosauria, with pseudosuchians first appearing in the late Permian and undergoing substantial diversification during the Triassic.

The group is highly diverse, including armored herbivores such as aetosaurs, large predatory forms like rauisuchians, long-snouted carnivores such as phytosaurs, and the crocodylomorphs, the lineage giving rise to modern crocodilians. A common anatomical feature of pseudosuchians is a crurotarsal ankle joint, which reflects a crocodile-like limb arrangement in many lineages. However, there is substantial variation in body plans and ecologies across the clade, so no single morphology defines all pseudosuchians.

In the Triassic, pseudosuchians occupied a wide range of ecosystems and display a broad array of lifestyles, from terrestrial ambush predators to semiaquatic forms. Phylogenetically, the group includes both long-lived primitive lineages and more derived crocodylomorphs. The End-Triassic extinction affected many pseudosuchians, but the crocodylomorph lineage survived and continued to diversify, eventually giving rise to the modern crocodilians and their fossil relatives.