 Like those of most other non @-@ avian theropods , Acrocanthosaurus forelimbs did not make contact with the ground and were not used for locomotion ; instead they served a predatory function . The discovery of a complete forelimb ( NCSM 14345 ) allowed the first analysis of the function and range of motion of the forelimb in Acrocanthosaurus . The study examined the bone surfaces which would have articulated with other bones to determine how far the joints could move without dislocating . In many of the joints , the bones did not fit together exactly , indicating the presence of a considerable amount of cartilage in the joints , as is seen in many living archosaurs . Among other findings , the study suggested that , in a resting position , the forelimbs would have hung from the shoulders with the humerus angled backwards slightly , the elbow bent , and the claws facing medially ( inwards ) . The shoulder of Acrocanthosaurus was limited in its range of motion compared to that of humans . The arm could not swing in a complete circle , but could retract ( swing backwards ) 109 ° from the vertical , so that the humerus could actually be angled slightly upwards . Protraction ( swinging forward ) was limited to only 24 ° past the vertical . The arm was unable to reach a vertical position when adducting ( swinging downwards ) , but could abduct ( swing upwards ) to 9 ° above horizontal . Movement at the elbow was also limited compared to humans , with a total range of motion of only 57 ° . The arm could not completely extend ( straighten ) , nor could it flex ( bend ) very far , with the humerus unable even to form a right angle with the forearm . The radius and ulna ( forearm bones ) locked together so that there was no possibility of pronation or supination ( twisting ) as in human forearms . 
