Chapter 4: Teeth Everywhere

1. Teeth make great fossils – why are they “as hard as rocks?”

Teeth are “as hard as rocks” because of the high hydroxyapatite (Ca5(PO4)3(OH)) content in them. It is more prevalent in teeth than even in bone, so teeth are less likely to decay and are more likely to be the best-preserved part of an organism’s fossil. The mineral is more frequent in the enamel of teeth,providing ample protection from decay if fossilized in decent conditions. However, soft organs are easier to decompose, so few organs are actually fossilized as well as teeth and bone. Because these two structures are common to many organisms, as seen in Chapter 2 with the discussion of homology.

2. What are conodonts? What extant species contains them?

Conodonts are organisms with protruding spikes, whose fossils have been found on every continent. They became used by jawless fish as teeth, since their spikes could cut food. Over time, through endosymbiosis, the fish acquired the conodont genes for producing hard teeth. This is particularly relevant to lampreys, an extant species which contains conodonts.

3. Shubin writes that “we would never have scales, feathers, and breasts if we didn’t have teeth in the first place.” (p. 79)  Explain what he means by this statement.

Scales, feathers, breasts, and teeth start are the lower layers of skin fold inward (similar to a plasma membrane). From these folds, each of the mentioned structures emerges, as shown in the figure below:

Shubin claims that the process for making teeth came first, and it then was changed to create other structures on the surface of the skin. Therefore, the existence of teeth allowed for hair, feathers, and breasts to develop. These structures are all derived from the ecdoderm, whose discussion can be found in Chapter 6.

Leave a comment


  1. Interesting to think of how evolution of these structures occurred. Don’t forget, random mutation enables the existing transcription factor/DNA interactions to be slightly altered, so given ample geologic time, it’s not too farfetched to see where this hypothesis could work, along with environmental change, ie, selection pressure change.

  2. StephanieZhong

     /  April 29, 2012

    Really interesting how a structure that we take for granted and that seems relatively unimportant allowed for the rise of other animal features today. In addition, it’s quite fascinating to know that teeth are some of the most lasting fossils, as opposed to the traditional types of fossils that we typically associate with skeletal bones.

  3. ngjenny

     /  May 1, 2012

    I have to agree with @StephanieZhong, because it is a bit counterintuitive to fathom teeth as something that came before these other structures since functionally they are fairly specialized. It’s also strange to consider how the ‘inner’ structures developed from each other as opposed to considering their development based on arrangement on the human body.


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