It had a extended neck, a short toothless mouth, and the bones in its wrists were compound together, much like that of the current day cockatoo. It had the ability to fold its whole arm next to its body, much like the wings of a bird. Unlike a bird however, A. portentosus had a long bony tail and its pelvis resembles that of extra theropod dinosaurs. It is probable that A. portentosus had feathers; however, the deposits in which it was establish are too coarse for such features to be preserved. Even if it did have fine hair, it seems unlikely that it would be able to realize flight, due to its large body.