By Eve Broughton
You are walking on the beach. There is a dark head poking out of the ocean watching you. What is it? Does it have external ears? If not, it is a seal. Sea lions, which tend to be less curious, do have external ears.
There is another large difference between seals and sea lions. While both have streamlined bodies adapted to aquatic life, the seal has gone further down this path. Its pelvis is greatly reduced and its thigh bone (femur) is gone. As a consequence, the seal is very clumsy on land; it has to pull its body along using the front flippers. In the water, they swim by undulating their bodies and using their rear flippers.