Euenantiornithes

Euenantiornithes

Enantiornithes is an extinct group of primitive birds. They were the most abundant and diverse avialans of the Mesozoic. Almost all retained teeth and clawed fingers on each wing, but otherwise looked much like modern birds externally. Over 50 species of Enantiornithines have been named, but some names represent only single bones, so it is likely that not all are valid. Enantiornithine birds went extinct at the Cretaceous–Paleogene boundary, along with hesperornithine birds and all other non-avian dinosaurs, and many other mostly reptilian life forms. Enantiornithines are thought to have left no living descendants.

Most researchers place Enantiornithines in Aves, but those that use the more restrictive crown group definition of Aves put them in the more inclusive Avialae, specifically, as members of the clade Ornithothoraces. Enantiornithines were more advanced than Archaeopteryx or Confuciusornis, but in several respects more primitive than all modern birds (Neornithes), perhaps following an intermediate evolutionary path. Due to the primitive features, some early studies placed Enantiornithes with Archaeopteryx in the paraphyletic grouping Sauriurae, but few researchers still do so.

A consensus of scientific analyses indicates that Enantiornithes is one of two major groups of birds within the Ornithothoraces. The other group is the Ornithurae, which includes all living birds as a subset. This means that Enantiornithines are a successful branch of bird evolution, but one that diversified entirely separately from the lineage leading to modern birds. The consensus on the reality of this basic two-way split has never been universally accepted and has been challenged by some studies, and it is possible that enantiornithines may actually represent successive outgroups of the lineage leading to modern birds.