Neornithes

Neornithes are the most recent common ancestor of all living birds and all their descendants. There are about 9,000 to 10,000 known living species in the world.

Taxonomy

Modern birds are divided into two superorders; the Palaeognathae (tinamous and flightless ratites), and the Neognathae, containing all other birds.

It is generally agreed that the Neornithes evolved in the Cretaceous and that the split between the Palaeognathae and Neognathae, and then the split between two subgroups of Neognathae, Galloanserae and Neoaves, occurred before the K-Pg extinction event. However, fossils that can be unequivocally assigned to the Neognathae, such as Vegavis and Asteriornis do not appear in the fossil record until the very end of the Cretaceous.

However, there are different opinions about whether the radiation within these major groups occurred before or after the extinction of dinosaurs. The only Cretaceous fossils that can be unequivocally assigned to the Neognathae are Vegavis and Asteriornis, two early members of the Galloanseres that corroborate the early diversification of this groups before the K-Pg extinction event. But the fossil record of Neoaves is restricted to post K-Pg times. Molecular dating have produced a wide range of dates for the rapid early diversification of Neoaves, from the late Cretaceous to the early Paleogene, with some studies suggesting that the rapid radiation largely coincided with the extinction event.