While exploring the coasts of east Darwin (some made up name), you find the skeleton of an apparently large organism on the beach. The skeleton is approximately 25m long, and appears to be some type of vertebrate-like organism. The organism has four relatively short limbs, attached to a heavy pectoral and pelvic girdle. There is no soft tissue left on the skeleton to assist you on your investigation. Because of it's location, you are at first unsure if it is an aquatic organism that washed up on the beach, or a terrestrial organism that died near the seashore. What skeletal structures would you look for to determine if it was aquatic or terrestrial? Explain why the structures you have mentioned are important in determining aquatic or terrestrial origins for the organism?