Enantiornitheans

Enantiornitheans, also called enantiornithines, are an extinct clade of birds within Avialae that flourished during the Cretaceous period. They were among the most diverse and widespread avialans of the Mesozoic, with fossils found on several continents and a particularly well-represented record in the Jehol Biota of East Asia. They persisted until the end of the Cretaceous, when they went extinct in the mass extinction event that also eliminated non-avian dinosaurs.

A defining feature of enantiornitheans is the reversed, or opposite, articulation of the shoulder girdle compared with modern birds. This shoulder arrangement, along with a mix of primitive and derived skeletal traits, distinguishes them from other early birds. Many enantiornitheans retained teeth in their jaws, though some evolved beaks. Their skeletons show a range of sizes and adaptations, and impressions of feathers in several species indicate elaborate plumage and complex wing feathers suitable for powered flight.

Ecologically, enantiornitheans occupied diverse niches. They were generally arboreal and insectivorous, but the group included species of varying sizes that may have fed on small vertebrates or fish. Their perching feet and wing morphologies reflect a variety of flight styles and habitats, from forest canopies to more open environments.

The fossil record is especially rich in China and other parts of the world, providing important insights into early bird evolution, plumage, and development. While they share a common ancestor with the lineage that led to modern birds, enantiornitheans are not direct ancestors of Neornithes. Instead, they form a distinct, now-extinct branch within Ornithothoraces that disappeared at the end of the Cretaceous.