If you’re a mammal – and I suspect you are – your teeth are arguably the most important part of your body, at least to a palaeontologist like me.
You see, teeth are the hardest tissues in the body, and as a result often the only record we have of extinct mammals. Luckily, we can use mammal teeth to identify the species to which they belong.
Fossil teeth also provide a wealth of biological information that we can use to understand things about extinct mammals that we otherwise can’t observe (at least not without a time machine).
We start with what we’ve learned from studying the teeth of living mammals.
Mammals, of course, have a variety of diets. As a simple example, tigers eat deer, while horses eat grass. Mammal teeth thus come in a variety of characteristic shapes because they provide a variety of functions, including pulverizing, slicing, and grinding.
The fact that mammal teeth have characteristic shapes related to their function is lucky for palaeontologists because it enables us to immediately understand some very basic things about the biology of extinct mammals from their teeth, for example whether an ancient animal was an herbivore or carnivore.
However, it’s not always so clear cut.
The polar bear (Ursus maritimus) and raccoon (Procyon lotor) have very similar teeth but very different diets. Polar bears eat seals while raccoons are omnivores. So, how do we distinguish between species with relatively similar chompers?
One way is to use high-tech, 3D imaging methods that enable us to identify minute differences in tooth shape that correspond to seal skewering, or in the case of urban raccoons, a diet of garbage.
Teeth also record the chemical composition of what an animal eats and drinks during its life.
The chemical formula for water is H2O; a molecule of water has two hydrogen atoms and one oxygen atom. But natural water actually comes in a range of different isotopic varieties. (An isotope is a natural variant of an element, such as oxygen, with an identical number of protons, but varying numbers of neutrons). The ratio of different oxygen isotopes in a body of water depends on many factors, including the water’s temperature and salinity. Thus, water from different sources, such as lakes, rivers or wetlands, have slightly different oxygen isotope compositions.
While teeth are growing, whenever an animal drinks water these oxygen isotope differences are incorporated into its tooth enamel. As a result, we can take samples of tooth enamel and learn a lot about what, and even where, an animal drank.
I hope that with this blog post I’ve given you something to chew on and convinced you that fossil mammal teeth are a lot more exciting than they initially sound — they certainly always give me a big smile when I find them!