* Sea otters have four legs, but their hind legs are much larger and more powerful than their front legs. They use their hind legs for swimming and propulsion in the water.
* Penguins also have four legs, but their legs are located very far back on their bodies and are short and thick. They use their legs for walking on land and for swimming in the water.
Even though they live in the ocean, both sea otters and penguins are mammals and birds, respectively. They have evolved to adapt to their aquatic lifestyles, but they still have the basic skeletal structure of their land-dwelling ancestors.