Archaeornithes now thought to represent a single species, "Archaeopteryx lithographica", the "Archaeornis" being the Berlin specimen of "Archaeopteryx". While rarely used by palaenthologists today, the term was revived by the ornithologists Livezey and Zusi in 2007, for a group comprising Archaeopterygidae and the Confuciusornithidae. Archaeornithes The Archaeornithes, classically Archæornithes, is an extinct group of the first primitive, reptile-like birds. It is an evolutionary grade of transitional fossils, the primitive birds halfway between non avian dinosaur ancestors and the derived modern birds (avian dinosaur). Fossils of early birds were poorly known until the late 20th century. Of those known, all fell into
Specimens of Archaeopteryx "Archaeopteryx" likely indicated it had very little flight ability. The furcula (wishbone) is well-preserved and lies between the scapulae; its boomerang-like shape reveals a 75-degree angle between its branches. De Beer identified a compressed mass of bone as a sternum in the London specimen, but later researchers disputed this as more likely to be a concretion of vertebrae encrusted by calcite. That "Archaeopteryx" lacked a bony sternum is in agreement with the modern consensus that many specimens of "Archaeopteryx", including the London, likely represented immature animals whose sterna were still cartilaginous. The pelvic girdle is separated into its three components