That is, what was its evolutionary antecedent? It’s made of keratin, not bone, so I’m guessing it’s unrelated to the teeth of their ancestors. Was it just hair near the whale’s mouth that developed into the rigid stuff we know today?
While not very thorough the link below is the best I found so far. Seems they are somewhat of a mystery still.
Baleen isn’t hair, and it’s unlikley that whales still had hair by the time baleen first arose. The baleen plates are essentially thickened skin, rather like a callous. There have been a lot of modifications over the eons of course, but it seems likely that the first plankton feeders lived rather like crabeater seals by using their teeth to filter to a limited extent. The keratinisation and extension of the gaps between the teeth helped make a tighter seal and improve efficiency, and over time they supplanted the teeth as the primary means of filtration.
But whales, even the baleen whales, still have hair now.
The remaining hair on cetaceans (whales, dolphins, and porpoises) is generally found near the mouth and often lost early in life, but some whales, such as Humpbacks, retain their hair in a few spots near the mouth throughout their lives.
You are correct about early baleen whales having sets of teeth: Aetiocetus is an extinct whale that had both a set of teeth and some baleen about 30 million years ago or so. Current thinking does lead towards the kind of scenario you describe with teeth as a pre-baleen filtering mechanism (right down to the similarity with crabeater seals), but I’m not sure about the callous-like skin notion. From what I understand, calloused skin does not contain concentrations of hydroxyapatite or other minerals found in baleen, just many layers of dead epithelial cells - making the baleen significantly different from calloused skin.
BTW, here and here are a couple good pages on Mysticete (baleen whale) evolution.
Oops! I see that my first cite is the same as Whack-A-Mole’s! Sorry!
This is contrary to all the baleen I have ever seen. Baleen is quite fibrous, as if hair is fused together. It can be teased apart into long strips, and Eskimo weavers create amazing baleen baskets from it. It is much more like hair than skin.
As I said, there have been a lot of modifications over the eons, but I have never heard anyone dispute that baleen is in essence simply keratinised skin before.
[a. Baleen is made of keratin (a protein that also composes hair and fingernails). It is strong, yet elastic.
b. Baleen plates arise in the fetus as thickenings of skin on the upper jaw. At birth, baleen is soft and short, but it soon stiffens.](http://www.seaworld.org/infobooks/Baleen/phycharbw.html)
Baleen: found in some whales, is a series of keratinized plates that arise from oral epithelium.
Perhaps those posters who dispute that baleen is keratinised epidermis can tell us why they dipute those refernces and presented alternative hypothises of wht it might plausibly be?
Simply saying ‘it doesn’t look like skin to me’ isn’t very scientific. Things can and do change radically under evolutionary pressure. That doesn’t alter the fact that a bat’s wings are essentially modified fingers, or that human teeth are essentially modified scales.
I’m not disputing that baleen arises from the skin or that it is primarily keratin. If you read my post above you’ll see that I’m saying baleen is not merely thickened skin like a callous. The formation of baleen requires creation of chemical and mineral components that do not appear in callouses as far as I know.
In fact, in your own cite #3 from wikipedia you can read about the additional components in baleen besides keratin. Even in the brief wikipedia article it will tell you that baleen has increased concentrations of hydroxyapatite, manganese, copper, boron, and calcium.
Whales actually do get callouses - particularly grey whales, who scrape along the bottom a lot to feed, and it’s pretty obvious that those are not like baleen.
I can understand why Fear Itself says baleen is more like hair than skin - to anyone who’s handled baleen this is obvious. It might not be obvious to everyone that hair is simply derived from skin. So both baleen and hair share that similarity. Blake, you’re right that baleen’s evolutionary origin is probably from skin, though, not from hair. It is also not simply a thickening of the skin like a callous, but is chemically different from a callous (it already has a variety of obvious structural differences from callouses - coming in plates, extruding from the skin in hair-like strands.)
Simply put, there was none:
From The Baleen of Mysticetes Grows on the Alveolar Process of Maxilla: Comparative Anatomy of the Fetus Minke Whale (.pdf document; pg 73):
From that same document, we have “PALATE VASCULARIZATION IN AN OLIGOCENE TOOTHED MYSTICETE (CETACEA: MYSTICETI: AETIOCETIDAE); IMPLICATIONS FOR THE EVOLUTION OF BALEEN”, which states:
Nantucket baskets also were made with baleen weavers.