In order to adapt to the underwater environment, the whale's forelimbs evolved into fins, and its hind limbs degenerated, resulting in a horizontal caudal fin. When the nostril moves to the top of the head, it needs to be exposed to the water at regular intervals to replace oxygen. No auricle, but excellent hearing.
The blue whale is one of the baleen whales in the baleen family and an endangered species in the World Conservation Union. It is not only the largest whale, but also the largest mammal in the world so far.