Evolution of birds extinction event 66 million years ago, giving rise to ostriches and relatives (Paleognathae), ducks and relatives (Anseriformes), ground-living fowl (Galliformes), and “modern birds” (Neoaves). Phylogenetically, Aves is usually defined as all descendants of the most recent common ancestor of a specific modern bird species (such as the house sparrow, "Passer domesticus"), and either "Archaeopteryx", or some prehistoric species closer to Neornithes (to avoid the problems caused by the unclear relationships of "Archaeopteryx" to other theropods). If the latter classification is used then the larger group is termed Avialae. Currently, the relationship between dinosaurs, "Archaeopteryx", and modern birds is still under
Specimens of Archaeopteryx Tischlinger & Unwin (2004), who reclassified it as part of the sternum, albeit minimally ossified (mostly cartilagenous). This supports the idea that the Berlin "Archaeopteryx" was not a full-grown individual at the time of its death, and instead represents an immature animal. The pelvis of the Berlin specimen was considered by Dames to be markedly different from that of the London specimen, which was a major point in favor of his assigning a new species to the Berlin "Archaeopteryx", "siemensii", after its generous donor. Other researchers, however, disputed this difference, claiming it could be entirely accounted for by deformation of