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 make it possible for the organisms to survive using filter feeding, such as a change in skull structure and throat elasticity. It would be highly unlikely for all of these changes to occur at once. Therefore, it is proposed that Oligocene aetiocetids possess both ancestral and descendent character states regarding feeding strategies. This makes them mosaic taxa, showing that either baleen evolved before dentition was lost or that the traits for filter feeding originally evolved for other functions. It also shows that the evolution could have occurred gradually because the ancestral state was originally maintained. Therefore, the mosaic whales could