晚侏罗世
The earliest avialans, which include birds and their ancestors, appear during the Middle to Late Jurassic, definitively represented by "Archaeopteryx" from the Late Jurassic of Germany. Avialans belong to the clade Paraves within Coelurosauria, which also includes dromaeosaurs and troodontids. The Anchiornithidae from the Middle-Late Jurassic of China have frequently suggested to be avialans, but have also alternatively found as a separate lineage of paravians.