[further discussion on this at:]
Introversion of external hair (armor) to internal "teeth"
Baleen whales (blue, humpback, right whales) developed their baleen (whalebone stringy teeth) on the upper jaw, because their fish & mollusc eating ancestors had had walrus-like mustache whiskers which gradually migrated from the upper lip into the upper gums (over a period of a million years), changing from nerve-rich sensory bristles to long net-like filters, straining krill and small fish while allowing water to escape the mouth. (This is one of my hypotheses, haven't seeen any confirmation from others.)
Extroversion of internal teeth to external scales (armor):
Lamphrey (and hagfish?) types lack jaws, but have replaceable teeth which are used to grasp. Is it possible that fish scales derived from multiple teeth replacing (like in sharks, but non-jawed) in a previously non-scaled lamphrey-like ancestor? Various fish scales do resemble teeth in some way, although many have become ultra-smooth for high-speed hydrodynamics. Do fish embryos develop their scales in a cephalo-caudal direction starting at the head? Do primitive scaled fish have more dental-like scales?
Is this a new idea, or has anyone heard of it before? (This is another hypothesis)
Anyway, just seems cool that the opposite actions may have happened in fish and whales.
[Now consider that birds have feathers, which have bloodflow in the plume, do feathers derive from vestigial teeth in early aves which were developing beaks and bills and reducing their ancestral dentition? Are feathers malformed teeth with roots? Where did the beak come from? I don't know.]
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