eureptilia

Eureptilia is a clade within Sauropsida traditionally defined as the group of reptiles that are more closely related to living reptiles than to the parareptiles. The name combines Greek eu- meaning true and reptilia. The group is thought to have originated in the Late Carboniferous to Early Permian, with early representatives such as Hylonomus among the earliest known eur eptilians.

Within Eureptilia, the major living lineages Lepidosauria (lizards, snakes, and tuataras) and Archosauria (crocodilians, birds, and their extinct relatives) are included, together with numerous extinct groups. The exact composition of Eureptilia varies among phylogenetic analyses; some frameworks place turtles (Testudines) within Eureptilia, while others position them outside. A consistent feature of many definitions is that Eureptilia excludes Parareptilia, an earlier and separate lineage of reptiles.

Evolutionarily, Eureptilia represents the divergence from parareptiles and the lineage leading to crown-group Reptilia. Within this clade, the archosauromorph and lepidosauromorph lineages gave rise to the diversity of reptiles seen in the Mesozoic and present day, including birds and many extinct reptile groups. The fossil record shows diversification of eureptilians during the Permian and Triassic periods, contributing significantly to reptilian evolution.

In contemporary usage, Eureptilia is less common in modern cladistic terminology, with many authors preferring Reptilia or Diapsida to designate crown-group reptiles. Nevertheless, the term appears in historical literature and some educational materials as a way to describe the “true reptiles” that exclude the earlier parareptiles, helping to frame early reptile evolution.