Baleen
Baleen is similar to bristles and consists of keratin, the same substance found in human fingernails, skin and hair.
They are also called baleen bristles, which in sei whales are highly calcified, with calcification functioning to increase their stiffness.
The initial evolution and radiation of baleen plates is believed to have occurred during Early Oligocene when Antarctica broke off from Gondwana and the Antarctic Circumpolar Current was formed, increasing productivity of ocean environments.
Using parsimony to study this and other ancestral characters suggests that the common ancestor of aetiocetids and edentulous mysticetes evolved lateral nutrient foramina, which are believed to have provided blood vessels and nerves a way to reach developing baleen.
If true, this combination of baleen and dentition in Aetiocetus would act as a transition state between odontocetes and mysticetes.
Therefore, the mosaic whales could have exploited new resources using filter feeding while not abandoning their previous prey strategies.
The result of this stepwise transition is apparent in modern-day baleen whales, because of their enamel pseudogenes and their in utero development and reabsorbing of teeth.
[3] If it is true that many early baleen whales also had teeth, these were probably used only peripherally, or perhaps not at all (again like Dall's porpoise, which catches squid and fish by gripping them against its hard upper jaw).
Intense research has been carried out to sort out the evolution and phylogenetic history of mysticetes, but much debate surrounds this issue.
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 flexibility and strength were required, including baskets, backscratchers, collar stiffeners, buggy whips, parasol ribs, switches, crinoline petticoats, farthingales, busks, and corset stays,[7] but also pieces of armour.
