; subphylum Vertebrata, superclass Gnathostomata)
The class that comprises all the birds. The late Jurassic Archaeopteryx lithographica is still the best-known Mesozoic bird, but others have been described since the 1980s: Noguerornis, from the lowermost Cretaceous of Spain; the slightly later and more advanced Concornis and Iberomesornis, known by complete skeletons, also from Spain; and, also early Cretaceous, Sinornis and Cathayornis from China. There were also some curious, specialized, Late Cretaceous birds, such as the flightless Mononykus from Central Asia, in which the forelimbs were reduced to stubby claws, and Hesperornis, a diving form. All these early birds had teeth and long, bony tails. Birds arose from within the theropod dinosaurs (Theropoda) and so should properly be classified as a subgroup of them; those closest were the Dromaeosauridae (the family which includes the famous Velociraptor of Jurassic Park).
Subjects: Zoology and Animal Sciences.