Eosuchian

Eosuchian is an extinct group of archosauromorph reptiles that lived during the Permian and Triassic periods. They are considered early relatives of modern crocodilians and birds. Eosuchians were characterized by a generally small to medium-sized body, with some species reaching up to two meters in length. They possessed a long tail and relatively short limbs. Their skull structure indicated they were likely primarily carnivorous, though dietary habits may have varied among species.

The fossil record of eosuchians is found in various parts of the world, including South Africa, Russia, and China. They are typically found in terrestrial or shallow freshwater environments. The exact phylogenetic position of eosuchians has been debated, but they are generally placed within the Archosauromorpha, a major clade that also includes dinosaurs, pterosaurs, and crocodilians. Some studies suggest they may be stem-archosaurs, meaning they are closely related to the last common ancestor of all archosaurs but fall outside the crown group.

Notable genera within this group include Eosuchus, Youngina, and Thchosaurus. The discovery of Eosuchus in the Late Permian deposits of South Africa was significant in understanding early diapsid evolution. The group became extinct by the end of the Triassic period, likely succumbing to environmental changes and competition from more derived archosaur groups that rose to prominence. Their extinction marked the end of a particular lineage in the early diversification of archosauromorphs.