Suchians

Suchians are a diverse clade of archosaurs that includes both extinct and extant (living) species, playing a significant role in the evolution of reptiles and birds. The term "suchian" originates from the Greek word *souchos*, meaning "crocodile," reflecting their close relationship with modern crocodilians. This group emerged during the late Triassic period, around 230 million years ago, and diversified extensively throughout the Mesozoic Era.

Suchians are characterized by their distinctive skull anatomy, particularly the presence of an antorbital fenestra—a bony opening in front of the eye socket. This feature is shared by crocodilians and pterosaurs, though it varies in size and shape among different lineages. The clade encompasses two primary branches: the Pseudosuchia (false crocodiles) and the Avemetatarsalia (bird-ankled reptiles). Pseudosuchians include large predatory dinosaurs like *Postosuchus* and *Alligatoroides*, while Avemetatarsalia gave rise to pterosaurs and, ultimately, birds.

Suchians were ecologically dominant during the Mesozoic, occupying roles as apex predators, scavengers, and even herbivores in some cases. Their success was partly due to adaptations such as powerful jaws, efficient respiration, and specialized teeth. The decline of many suchian lineages coincided with the Cretaceous-Paleogene (K-Pg) extinction event around 66 million years ago, though crocodilians survived and remain one of the few surviving suchian groups today.

Avemetatarsalia, particularly the lineage leading to birds, represents one of the most significant evolutionary transitions in vertebrate history. Modern birds are the only living descendants of suchians, demonstrating the long-term persistence of this clade despite the extinction of most other members. The study of suchians provides critical insights into the evolutionary pathways that shaped modern reptiles and the origins of avian flight.