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As a SciShow viewer, you can  keep building your STEM skills with a 30 day free trial and 20% off an annual premium subscription  at Brilliant.org/SciShow. Have you ever been in a museum,  staring down a mounted T. rex, and feeling incredibly grateful  that it’s not around any more because each of those teeth  are the size of a banana?

I’m asking for a friend. Fossilized teeth have way more  value than just inspiring awe, and sometimes terror, in museum visitors. They can tell paleontologists  a lot more than you’d think about the evolutionary  past, from a creature’s diet to when humans started to develop tools.

So, here’s what makes teeth a  paleontologist’s best friend. Teeth are hard, compact, and  already have a layer of mineralized tissue called enamel on the outside. This makes them an almost perfect specimen for preservation in the fossil record.

In fact, tooth enamel is one of the  hardest biological substances around. And enamel isn’t just protecting  a tooth during an animal’s life, it’s preserving its history for millions of years. Part of that history lies in the  shape and size of all the little nooks and crannies that make up a tooth’s shape.

There are the big differences  between teeth, like how square, smooth molars help some  animals munch all day on grass while sharp fangs help others bring down prey. But there are also more subtle similarities and differences in tooth anatomy  between closely related species. These anatomical features are passed down or evolve through generations,  meaning paleontologists can map tooth surfaces like a landscape  to start building family trees.

In some cases, teeth might be the  only fossils researchers have to work with in figuring out who’s related  to whom, since teeth keep so well. And if they look even closer,  scientists can see more signs of how an ancient creature lived. Because, if you think about  it, teeth are the only parts of our skeleton that interact  directly with the environment!

Every time an animal munches on, say, a leaf, tiny bits of silica from the  plant’s cells are dragged across the tooth’s surface leaving a  trail of microscopic scratches behind. Or, if it’s gnawing on a  nut, the hard chunks pound microscopic pits into the tooth. Paleontologists call this a foodprint,  and it tells them what an animal ate, at least in the weeks leading up to its death.

But that’s still a really  valuable source of dietary info. Sometimes, researchers might  find tiny micro-fossils or bits of preserved food that got stuck on the teeth, which helps them confirm their suspicions. And teeth can tell paleontologists more than just what was going on in the  mouths of ancient animals.

They can give us clues about other  parts of their bodies, as well. Take ancient humans for example.  Like the rings of a tree, scientists can count the  growth lines in their enamel to get a sense of a person’s age or health. See, as teeth mature and develop,  new layers of enamel are laid down through a process called amelogenesis.

As that process speeds up or slows  down, it leaves bands in the enamel. And because this happens in a 24 hour cycle, those growth lines can show  how old a prehistoric human was when they died. Kind of like tree  rings, but for days instead of years.

Since your teeth stop growing eventually, it tells us the most about an  individual’s juvenile years. /Defects/ in that growth can  also show that a person was sick, stressed or malnourished during  a particular time of their lives, since those things affect how well  teeth can lay down new enamel layers. In 2022, scientists used teeth  from primates in the fossil record to model how early humans grew during pregnancy. The big brains of anatomically  modern humans take some time to grow.

The researchers showed that the  proportions of a species’ teeth are related to both its brain  size, and how long it takes to develop in the womb. So by studying the proportions of  teeth from different primate species, researchers could predict when early human brains started to evolve to be bigger. And that’s not the only way our  teeth changed as we evolved.

As early humans started to  develop tools and cook with fire, that was reflected in their teeth. For example, teeth evolved to become smaller as we started cooking with fire, since the heat was doing a lot of the food breaking down for us, not our chompers. Teeth from early humans like  Australopithecus are relatively large teeth, whereas those from Homo erectus  onwards were much smaller.

Which lets you guess who’s cooking. Plus, you can see the evolution of tool use in the wear patterns on ancient humans’ teeth. Neanderthals, for example,  used their teeth basically like an extra hand to hold  onto hides as they cut them.

Or they softened wood by chewing on it, or used their teeth to hold  onto leaves while weaving. And all that grasping and biting  left different patterns of scratches and scrapes on their teeth, which  paleontologists can now decipher to get a glimpse of prehistoric life. Early humans continued to use their teeth as a kind of extra tool for a while, but as their hand-held tools became more advanced, they used teeth less and less, and the teeth even shrunk as a consequence.

So ancient teeth are pretty darn  amazing for reconstructing not just what happened in the  mouths of prehistoric animals, but what their lives and interactions were like. And that makes them the perfect fossils for researchers to sink their teeth into. Now, if researchers had only  found teeth from animals that cooked their food, they wouldn’t  know about all of this tooth evolution.

And that would have just come  down to a sampling problem. But, luckily for us, there are resources  on the internet, like Brilliant, that teach us more about sampling bias. Their course on Sampling is a  great place to start drawing more accurate conclusions about a population.

This course starts with an intro  to sampling and estimation, and by the end, you’re learning  about the nuances of error and bias. In just 9 lessons, you’ll know what  makes a truly representative sample that reduces bias and helps draw more broadly informative conclusions  about the world around you. To get started today, head  to Brilliant.org/SciShow or click the link in the description down below.

That link will give you a free 30 day trial and 20% off an annual premium Brilliant subscription! And thanks for thinking critically  with Brilliant and SciShow. [OUTRO]