Birds evolved from certain feathered theropod dinosaurs, and there is no real dividing line between birds and non-avian dinosaurs except that some of the former survived the Cretaceous–Paleogene extinction event while the latter did not. For the purposes of this article, a 'bird' is considered to be any member of the clade Aves in the broadest sense. Some dinosaur groups which may or may not be true birds are listed below under Proto-birds.
This page contains a listing of prehistoric bird taxa only known from completely fossilized specimens. These extinctions took place before the Late Quaternary and thus took place in the absence of significant human interference. While the earliest hominids had been eating birds and especially their eggs, human population and technology was simply insufficient to seriously affect healthy bird populations until the Upper Paleolithic Revolution. Rather, reasons for the extinctions listed here are stochastic abiotic events such as bolide impacts, climate changes due to orbital shifts, mass volcanic eruptions etc. Alternatively, species may have gone extinct due to evolutionary displacement by successor or competitor taxa – it is notable that an extremely large number of seabirds have gone extinct during the mid-Tertiary; this seems at least partly due to competition by the contemporary radiation of marine mammals.
The relationships of these taxa are often hard to determine, as many are known only from very fragmentary remains and due to the complete fossilization precluding analysis of information from DNA, RNA or protein sequencing. The taxa listed in this article should be classified with the Wikipedia conservation status category "Fossil".
Before the late 19th century, when minerals were still considered one of the kingdoms of binomial nomenclature, fossils were often treated according to a parallel taxonomy. Rather than assigning them to animal or plant genera, they were treated as mineral genera and given binomial names typically using Osteornis ("bone-bird") or Ornitholithus ("bird fossil") as "genus". The latter name, however, is still in use for an oogenus of fossil bird eggs. Also, other animals (in particular pterosaurs) were placed in these "genera". In sources pre-dating the Linnean system, the above terms are also seen in the more extensive descriptions used to name taxa back then.
Taxonomic list of fossil prehistoric birds
Higher-level taxa are presented in likely or suspected phylogenetic order. Genus-level taxa and lower are sorted chronologically, in ascending order (i.e., older taxa first).
The higher-level groups of non-Neornithes are arranged based on the phylogeny proposed by Luis Chiappe, updated and expanded to incorporate recent research. The categories are inclusive in ascending order.
Taxonomic assignments, especially in the pygostylian to early neornithine genera, are still very provisional and subject to quite frequent change.
Basal Avialae (extinct) The most primitive "birds", usually still possessing a long bony tail with generally unfused vertebrae. Not all of these may be on the line of bird ancestors; whether they are not closer to other theropods groups than to the Avialae remains to be thoroughly tested (see Xiaotingia).
†Anchiornis huxleyi
†Aurornis xui
†Balaur bondoc
†Jixiangornis orientalis
†Xiaotingia zhengi
†Yandangornithiformes
†Yandangornithidae
†Yandangornis longicaudatus (Late Cretaceous) †Archaeopterygiformes †Archaeopterygidae [Archaeornithidae ; Archaeopteridae ; Archornithidae ]a †Wellnhoferia grandis (Late Jurassic) – possible synonym of Archaeopteryx †Archaeopteryx [Archaeornis ; Griphornis ; Griphosaurus ] (Late Jurassic) †Jeholornithiformes †Jeholornithidae †Dalianraptor cuhe †Jeholornis [Shenzhouraptor ] (Early Cretaceous)
Basal Pygostylia (extinct) The earliest birds with a modern pygostyle: a reduction and fusion of the tail vertebrae; possibly a paraphyletic group. Two types of pygostyle are known, a rod-shaped one found in Confuciusornithidae, Enantiornithes and some non-avian theropods such as Nomingia, and a plowshare-shaped one, only known in the lineage leading to modern birds. It is not certain that the pygostyles found in birds are indeed synapomorphies.