Digestive system of humpback whales stretching like an accordion. They allow whales to open their mandible to 90 degrees to gulp water and prey. They expel saltwater through the baleen plates, leaving behind krill and plankton. The whale's tongue plays a vital role in filter feeding, as it is used to push the water out of its mouth while keeping the prey trapped in its baleen bristles. As humpback whales do not have teeth, their food is swallowed whole and travels down the esophagus into the preliminary stomach (known as the forestomach) to be ground. Baleen whales have a multi-chambered stomach, divided into three distinct
Baleen whale toothed cetaceans (Archaeoceti) remained unknown until the extinct "Janjucetus hunderi" was discovered in the early 1990s in Victoria, Australia. Like a modern baleen whale, "Janjucetus" had baleen in its jaw and had very little biosonar capabilities. However, its jaw also contained teeth, with incisors and canines built for stabbing and molars and premolars built for tearing. These early mysticetes were exceedingly small compared to modern baleen whales, with species like "Mammalodon" measuring no greater than . It is thought that their size increased with their dependence on baleen. However, the discovery of a skull of the toothed "Llanocetus", the second-oldest