Thursday, August 16, 2012

that tooth thang


Currently, I’m interning at a raptor education center. Basically, I show people birds and explain all the cool things about them. Some people come in and ask really good questions like “can they see in color?” or “do they mate for life?” However, some people ask not-so-intelligent questions. The other day, a young presenter was holding an Eastern Screech Owl and was asked by a guest “what is that tooth thang in the middle of its face?”

The guest was referring to the bird’s beak.

Of course, I mentally shook my head and entertained thoughts about how ignorant one must be to not know a bird’s beak when one sees it. But later on, I began to think that maybe I was being narrow-minded. Is it so dumb so register a tooth and a beak in the same category? Could the beak be the evolutionary cousin of teeth? Perhaps.

I started looking into the matter, this time with my mind set to evolution mode. When you think about it, beaks are pretty unique and useful structures. Birds have them, and even turtles kind of have them. Some are curved into a sharp points and tear flesh. Some are flattened into a bill and sift solids from water. Some are heavy-set and can crack macadamia nuts with no problem. Others are long and tubular, perfect for sticking down into a flower and licking out nectar. Though avian beaks are diverse now, it does not change the fact that modern birds came from a single common ancestor from Dinosaura. So the beak came from a single evolutionary point. That begs the questions- why, when, and how?


Lindsay Zanno and Peter Makovicky published a study in Proceedings of the National Academy of Science where they used a wide variety of evidence to figure out what therapods ate (theropods are the two-legged dino forebearers to birds). Evidence included fossilized dung and tooth marks on fossils (remember what fossilized poo is called?! Brownie points!). They found that early therapods were largely herbivorous, but some later evolved to be omnivorous and eventually carnivorous.

Come to find out, beaks emerged FIVE separate times within Therapoda. The diverging phyla of little herbivorous dinos experienced the drift towards and pressure for omnivory, which favored selection for having a beak. One lucky lineage went on to spawn our friend Archaeopteryx, and consequently, all of the birds both past and present.

The real kicker here is that these early beaked creatures still had teeth. I entertained this lady’s question thinking that perhaps the beak arose from the same germ cells as the teeth. But no siree, teeth were still present within the beaks. Therefore, teeth are not the structural forbearers to the beak. Not even on a germ line level.

If the lady who asked about the owl’s beak was asking because she thought maybe the beak was the product of increased selective pressure for a ripping mechanism over grinding teeth, like herbivorous therapod forebearers had, then that question was pretty good. Bravo.

But judging by her description of the beak as that “tooth thang,” my first instinct was right. That lady asked a really, really, dumb question.

5 comments:

  1. "tooth thang" hahahaahaha

    I hope she doesn't have children. Ever.

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  2. I've been pondering lately...
    I can't understand how organisms, such as the deep, dark fish, that have bio-luminescent traits could have evolved these traits...
    Even over billions of years, how could an organism, even influenced by natural selection, begin to develop luminescent appendages?

    A fish, prone to dark and deep depths, which can not see food, and can not make other organisms around it's environment aware of it's presence, must immediately die. I can't see how an organism can develop an actual biological appendage that can illuminate.
    I can understand how a lizard, who blends into a rock, can survive longer than a lizard that doesn't, which in turn leads to only lizards that can blend into their surroundings, eventually leading into only blending lizards remaining on the planet.
    Can you help me understand how an organism could eventually develop an extraordinary trait like luminescence?
    I am perplexed
    '

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    Replies
    1. Matt,

      I'm all over it. I'll research it and post this week!

      Thanks for reading and being curious.

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    2. some octopus, i forget which species has co-evolved with Vibrio harveyi to produce luminescence. The luminescence helps the octopus hide its shadow and shape from its prey who view it from the bottom. The luminescence is controlled by quorum sensing (which is actually a very very cool subject.) and basically the octopus controls the population of the V. harveyi which in turn controls the bioluminescence. I guess it evolved because those particular octopus were more successful hunters.

      Not sure if that's how that one dangly light fish in the deep sea uses another species for its luminescence though but that may help.

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  3. #1 To answer your quiz: coprolite
    #2 Just to spread the nerd love...the "scientific term" for beak is rhamphotheca and is applied to this structure in both birds and turtles.

    Keep it up!

    ReplyDelete