The coracoscapular joint of neornithine birds—extensive homoplasy in a widely neglected articular surface of the avian pectoral girdle and its possible functional correlates

Abstract A survey is given of the morphological variation coracoscapular joint neornithine birds. In Mesozoic stem group representatives, coracoid exhibits a deeply concave cotyla scapularis, which articulates with globose tuberculum coracoideum scapula. This morphology likely to be functionally related development powerful supracoracoideus muscle and formation triosseal canal as pulley for tendon this muscle. birds, scapula either via or flat facies articularis, latter largely restricting movements paramedian plane. Ancestral state reconstruction suggests that scapularis plesiomorphic Neornithes articularis evolved at least 13 times independently within clade. For several lineages, transition can traced in fossil record, replacement cup-shaped by articular facet seems have been due various functional demands. Often, associated reduced shafts furcula. weakly developed furcula enables transverse therefore restriction mobility taxa large crop, reorganization pectoral musculature, whereas procellariiform from appears correlated capacity sustained soaring without wing flapping.