Evolution? > Inside their pectoral fins, dolphins have a skeletal structure similar to a human arm and hand. They have a humerus, complete with a ball and socket joint. They have a radius and ulna, as well as a complete hand structure, including five phalanges, or finger bones. > The same goes for a sea turtle, a seal, a manatee and a whale. > All of these animals had four-legged ancestors that lived on land. What about the Platypus that is only found in Australia and Tasmania?