Filter feeder gap between the two rows of baleen plates lets the water in together with the prey, while the baleens filter out the water. Rorquals such as the blue whale, in contrast, have smaller heads, are fast swimmers with short and broad baleen plates. To catch prey, they widely open their lower jaw — almost 90° — swim through a swarm gulping, while lowering their tongue so that the head's ventral grooves expand and vastly increase the amount of water taken in. Baleen whales typically eat krill in polar or subpolar waters during summers, but can also take schooling fish, especially
Aetiocetus other edentulous, or toothless, mysticetes, the pattern of nutrient foramina is most similar to extant balaenopterids (blue whales and other rorquals) and fossil cetotheres. How did "Aetiocetus" feed, and what did it feed on? Its teeth are reminiscent of the bite-and-swallow strategy of archaeocetes and odontocetes, but they also possessed expanded palates. Modern mysticetes grow their baleen from this expanded palate and use the baleen to trap arthropods and fish in their mouths. This is known as bulk-feeding, in that the whale is not selecting individual prey items and does not use echolocation to find prey, as odontocetes do. Fossil