During his re @-@ examination of Iguanodon , David Norman was able to show that this posture was unlikely , because the long tail was stiffened with ossified tendons . To get the tripodal pose , the tail would literally have to be broken . Putting the animal in a horizontal posture make many aspects of the arms and pectoral girdle more understandable . For example , the hand is relatively immobile , with the three central fingers grouped together , bearing hoof @-@ like phalanges , and able to hyperextend . This would have allowed them to bear weight . The wrist is also relatively immobile , and the arms and shoulder bones robust . These features all suggest that the animal spent time on all fours .