Baleen

Baleen or whalebone is the means by which baleen whales feed. These whales do not have teeth, but instead have rows of baleen plates in the upper jaw – flat, flexible plates with frayed edges, arranged in two parallel rows, looking like combs of thick hair. Baleen is not bone, but is composed of keratin, the same substance as hair, horn, claws and nails.

Evolution of baleen
The oldest true fossils of baleen are only 15 million years old, but baleen rarely fossilizes, and scientists believe it originated considerably earlier than that. This is indicated by skull modifications which are associated with baleen (such as a buttress of bone found beneath the eyes in the upper jaw, and loose lower jaw bones at the chin), being found in fossils from considerably earlier. Currently, baleen is believed to have evolved around thirty million years ago, possibly from a creature with a hard, gummy upper jaw, similar to that found on Dall's porpoise today, which are, at a microscopic level, almost identical to baleen.

Curiously, many early baleen whales also had teeth, but these were likely used only peripherally, or perhaps not at all (again, similar to Dall's porpoise, which catches squid and fish by gripping them against its hard upper jaw).