The Beak is NOT a Lie

The turtles and birds are the only living archosaurian animals today with a “beak,” a keratinized rhamphotheca covering the margins of the jaw [n1]. These features are associated with a lack of teeth, which has caused a question of correlation: Whether the absence of teeth in fossils indicates the presence of a beak. I talked about assessing this correlation for turtles here, but today I am expanding on the other taxon I mentioned here, Amazona ochrocephala ochrocephala.

Unlike the turtle, the parrot’s beak here is much, much thinner in cross-section. The dorsal lamina of the rhamphotheca, covering the dorsal surface of the mandibular symphysis, is parallel to and close to the ventral lamina. Similarly, the rostral margin of the bony region of the symphysis is highly porous, thus the shape of the rostral bony beak doesn’t match the rhamphotheca overlying it. This results in a larger extension of the rhamphothecal portion of the beak than the bone. It further suggests that turtle beaks are easier to “guess” the shape of the living beak than in parrots.

Caveat: Not all birds match this morphology, this holds primarily for parrots, and in some birds the beak matches the bone more closely.

[n1] As Jerry Harris in the comments below points out, of course I failed to mentioned that more than just turtles and birds have “beaks,” keratinized structures, hard or soft, formed around or within the oral tissues. Eventually I should get to covering them too, and soon.

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3 Responses to The Beak is NOT a Lie

  1. dinogami says:

    The turtles and birds are the only living animals today with a “beak,” a keratinized rhamphotheca covering the margins of the jaw.

    Jaime…! For shame! This is not, of course, true. Platypuses have keratinized beaks among mammals, and several fish (e.g., parrot fish) have keratinized beaks. I think birds may be the only ones with beta-keratin in the beak (turtles apparently have only alpha-keratin, as in mammals), but they’re all keratinized beaks. I’m guessing you meant to put in some other, more restrictive criterion…?

    • ….PFFFFFFT….

      My coffee….

      Well, clearly I meant archosaurian, or some such special, magical qualifier. I shall emend. (I never meant to exclude their furry cousins, although platypi have much SOFTER beaks, and I was trying to embody the hardened keratinized beaks, and failed). I was not considering fish at all when I wrote the post. It was not as detailed on the subject, or as careful, as the first post on turtle beaks.

  2. Pingback: Turtle beak | Playstation3st

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