Digestive system of humpback whales Digestive system of humpback whales The digestive system of humpback whales ("Megaptera novaeangliae") is adapted to digest tiny crustaceans such as krill, plankton, and small fish (including herring and mackerel) which the whale filters from the ocean using its baleen, a sieve-like structure in the upper jaw. Humpback whales belong to the parvorder baleen whales, which are carnivorous, seasonal feeders. The baleen, a sieve-like structure in the upper jaw made of keratin, is used to filter plankton, among other food sources, from the water. Ventral grooves are expandable concave furrows that line a whale's throat and have the peculiarity of
Baleen whale mysticete, yielded a total length of , indicating filter feeding was not a driving feature in mysticete evolution. The discovery of "Janjucetus" and others like it suggests that baleen evolution went through several transitional phases. Species like "Mammalodon colliveri" had little to no baleen, while later species like "Aetiocetus weltoni" had both baleen and teeth, suggesting they had limited filter feeding capabilities; later genera like "Cetotherium" had no teeth in their mouth, meaning they were fully dependent on baleen and could only filter feed. However, the 2018 discovery of the toothless "Maiabalaena" indicates some lineages evolved toothlessness before baleen. "Mystacodon