416-359 million years ago


Eusthenopteron was a sarcopterygian fish (a rhipidistian, to be more precise) which had bones in its fins homologous to tetrapod limb bones (humerus, radius, ulna, femur, tibia, fibula). The pectoral girdle (the bones which attach the arm/forelimb to the rest of the skeleton) was still attached to the skull so that there were a few bones which are lost in the first amphibians. The organization of its skull was very similar to the first amphibians (they are much more similar to each other than either is to modern fish or modern amphibians). Eusthenopteron has the same basic organization of bones in its fins as tetrapods had in their limbs with the exception of lacking a wrist, ankle, hand and foot. There were a number of cartilaginous fin rays in the general area that would later compose the tetrapod hands and feet.

pectoral fin

pelvic fin

pectoral fin and shoulder girdle