The scapulocoracoid of flightless birds: a primitive avian character similar to that of theropods

Abstract

The scapula and coracoid of the first bird Archaeopteryx represents a highly specialized morphology approaching that of modern carinate birds, with the scapula meeting the coracoid at an angle of approximately 90o. The primitive condition of the avian scapula and coracoid is exhibited by the flightless ratites, birds exhibiting many other primitive characters of the skeleton, either retained from primitive ancestors or derived through neoteny. The fact that the scapulocoracoid of ratites is the primitive condition is confirmed by its presence in the embryos of certain birds, and its presence through neoteny in other unrelated birds that have secondarily evolved Sightlessness. This morphology of the primitive avian scapulocoracoid closely approaches that of theropod dinosaurs, such as Deinonychits, and may well indicate relationship between the two groups.