codfish

— Codfish include ten families with more than 200 species. Almost all live in cold salt water in the Northern Hemisphere. Cod were thought to have developed into their current forms about 120 million years ago in the Tethys Sea, a tropical sea that once ran around the earth east-west and connected all other oceans. Eventually the Tethys merged with a northern sea, and the cod became a fish of the North Atlantic. Later, when a land bridge between Asia and North America broke, cod found their way into the northern Pacific. In gadiform fish, evolution is seen in the fins.