Teeth are really useful tools for paleontologists. In fact, they are the reason we even know some organisms existed. Those organisms didn’t have any other hard parts (that would easily fossilize).
Shubin describes some of his early days as a fossil hunter. I’ve been there where he was too. It’s just as he described it. You have to look for something that doesn’t look like rock, which isn’t nearly as easy as it sounds. But once you find the first one, it becomes much easier to find more.
These are entertaining stories. It’s really great when you find a scientist who is willing to share these stories and can do so in an entertaining way.
Anyway, back to teeth. Shubin says this about teeth
Much of the story of mammals is the story of new ways of processing food.
He describes a group of primitive mammal-like animals called trithelodonts (literally “three-knob teeth”). This was some of the earliest specialization in the shape of teeth.
Humans (and other mammals) have very specialized teeth. Incisors for cutting, canines for holding and molars for grinding. The entire order of carnivores is defined by four teeth called carnassials. If you have those kind of teeth, you are a member of the carnivore family, if you don’t have those teeth, you can’t be in that family. (Note that the family is different from the ability to eat meat.)
But where did teeth even come from? That’s an interesting story in and of itself.
The earliest teeth in the fossil record come from Conodonts. For a very, very long time, no one knew what animals was associated with these millions of fossil cone-shaped things that could be found all over the place.
Now, we know that these fossils were the first teeth. They were the teeth of lampray-like organisms that used them to bore into the flesh of fish and suck their blood.
Now, here’s where it gets interesting. You see, there is significant evidence that teeth were the first hard part ever. And further, that teeth are the original source of all hard parts of vertebrate animals. Everything from specialized teeth, bones, and armor on some species all came from teeth.
In this image, we see that the ‘armor’ on the earliest armored fish looks exactly like the tooth structure of Conodonts.
It goes even further than that. The development of teeth began a whole trend in the way organisms modify structures. You see, teeth develop by an interaction between two layers of tissue in our skin. Certain proteins in the outer layer of skin produce enamel and the inner layer produces the dentine and pulp of the inside of the tooth.
This process is the same for all systems that develop in the skin. Teeth, feathers, hair and fur, even mammary glands all result from this process. The genes that turn on all these feature are remarkably similar.
Teeth are the common ancestor of everything that comes from the skin. We couldn’t have hair or even mammary glands without the development of teeth 500 million years ago.
We begin to see that everything in our bodies is based on simple changes (relatively) to already existing systems.