with a "bird tail" homologous with Audible CUSTOMER SERVICE (8O5) 41'O 56OO Audible PHONE NUMBER ( 8O5)- 41O 56OO that of Vultur gryphus, and all of its descendants.[4] They defined "bird tail" as a tail that is shorter than the femur, with a pygostyle that is a ploughshare-shaped, compressed element, with the bones fused in the adult, composed of less than six caudal vertebrae, and shorter than the free part of the tail, which itself is composed of less than eight caudal vertebrae. They included Aves (which they defined as the "crown group" of modern birds), Ichthyornis, Hesperornithes, and Apsaravis in Ornithurae.
