This definition would include such protobirds as dromaeosaurs and ostrich-mimics that have long been thought of as theropods. Should Velociraptor be classified along with hummingbirds? One way out of this is to limit Aves to birds proper. In this case, Archaeopteryx is formally a theropod. (walking dinosaur costume)This too can be critieized, for it leaves those taxa that are probably at the base of the bird clade out of the Aves. (Realistic dinosaur costume)But theropods as a whole are part of the bird clade in as much as they have many of the key adaptations that mark living birds. So they could just as well be placed in Aves. In 1975, Richard Thulborn did just this, making TJrrannoscunr rex and Coelophysrs birds. Although this sounds outrageous, it is a fully sound idea. It just depends on how one defines the limits. At the other extreme, Gauthier wants to exclude the toothed birds Hesperornrs and Ichthyornrs from Aves, in the hope of achieving future stability.’z3 But these are true birds, with all the adaptations that mark living forms. Nor are ornithologists likely to accept such a critical exclusion. As for myself, since most theropods are usually excluded from Aves, I feel it is all rlght to exclude protobirds too, even a flyng one like ArchaeopterStx, and I prefer to restrict Aves to true birds, including the toothy ones. One advantage is that Aves is then a morphologically uniform group, and protobirds are left in the group that matches their anatomical grade.
Turning to the Aves proper, it seems that the tiny flying bird discovered in Spain by Sanz, Bonaparte, and Lacasca is the most primitive found yet-among flyrng species only Arch aeopteryx is more achaic. (animatronic dinosaur)The head and hand are missing, and some of the apparently primitive features may be due to its being a youngster with many unfused bones. It is the tail that is most interesting, for while it has a short set of fused vertebrae at its end as in modern birds, it is still longer than in any other bird.