 "Archaeopteryx" has historically been considered the first bird, or "Urvogel".Although newer fossil discoveries filled the gap between theropods and "Archaeopteryx", as well as the gap between "Archaeopteryx" and modern birds, phylogenetic taxonomists, in keeping with tradition, almost always use "Archaeopteryx" as a specifier to help define Aves.Aves has more rarely been defined as a crown group consisting only of modern birds.