The orientation of the shoulder joint was sideways, instead of angled upward as in modern birds; this means that "Confuciusornis" was unable to lift its wings above its back. Like "Archaeopteryx", it was thus incapable of the upstroke required for flapping flight. This conclusion is not established at present. Peters sees "Confuciusornis" as capable of flapping flight but specialising in soaring flight. The bird's weight has also been debated. 