Baleen this issue. A whale's baleen plates play the most important role in its filter-feeding process. To feed, a baleen whale opens its mouth widely and scoops in dense shoals of prey (such as krill, copepods, small fish, and sometimes birds that happen to be near the shoals), together with large volumes of water. It then partly shuts its mouth and presses its tongue against its upper jaw, forcing the water to pass out sideways through the baleen, thus sieving out the prey, which it then swallows. People formerly used baleen (usually referred to as "whalebone") for making numerous items where
Baleen whale of the world, necessitating more efficiency traveling over long distances between widely distributed prey sources which also resulted in a lower metabolic rate, and feeding on baitballs. A 2017 analysis of body size based on data from the fossil record and modern mysticetes indicates that the evolution of gigantism in baleen whales is a recent phenomenon, estimated to have occurred within the past 3.1 Ma. Before 4.5 million years ago, few mysticetes exceeded 10 meters (33 feet) in length; the two largest miocene species were less than 13 m in length. The initial evolution of baleen and filter feeding long