Shoulder - Evolutionary Variation

Evolutionary Variation

Tetrapod forelimb are characterised by a high degree of mobility in the shoulder-thorax connection. Lacking of a solid skeletal connection between the shoulder girdle and the vertebral column, the forelimb's attachment to the trunk is instead mainly controlled by serratus lateralis and levator scapulae. Depending on locomotor style, a bone connect the shoulder girdle to the trunk in some animals; the coracoid bone in reptiles and birds, and the clavicle in primates and bats; but cursorial mammals lack this bone. In primates, the shoulder shows characteristics the differs from other mammals, including a well developed clavicle, a dorsally shifted scapula with prominent acromion and spine, and a humerus featuring a straight shaft and a spherical head.