Eusuchia

Eusuchia is a clade of crocodyliform archosaurs that includes all living crocodilians and many of their extinct relatives. The name means “true crocodilians,” reflecting its close relationship to modern Crocodylia.

In many phylogenetic analyses, Eusuchia is defined as a crown group within Crocodylomorpha, consisting of organisms more closely related to modern crocodilians than to more primitive crocodyliforms. The group is characterized by a derived skull and palate morphology, including a well-developed secondary palate and changes to the palatal openings that support an expanded airway. These features underpin an efficient breath-control system and are among the key synapomorphies used to diagnose eusuchians in the fossil record.

The eusuchian fossil record ranges from the Late Jurassic to the present. Stem eusuchians appear in the Jurassic and early Cretaceous, and the lineage gives rise to the diverse array of extinct eusuchians that flourished in various environments through the Cretaceous and Cenozoic. Today, Eusuchia includes the three living crocodylian families: Alligatoridae (alligators and caimians), Crocodylidae (true crocodiles), and Gavialidae (gharial).

Distribution and ecology today reflect the broad tropical and subtropical settings occupied by modern crocodilians. They inhabit freshwater and brackish environments across the Americas, Africa, Asia, and parts of Australia. As a clade, Eusuchia represents the evolutionary backbone of the crocodilian lineage, bridging ancient crocodyliform diversity and the modern diversity of crocodilians.