The modern sea otter evolved initially in northern Hokkaidō and Russia, and then spread east to the Aleutian Islands, mainland Alaska, and down the North American coast. Sea otters have evolved into two categories, one of which consists of those sea otters that primarily eat fish, and the other is made of those that eat primarily invertebrates.
Also, Modern Day Sea Otters have adapted to be able to use tools and having a coat of fur that helps them keep warm and float.
DAO Environmental Science Keystone Species 