Our teeth are on the front line of this struggle. As mammals have become specialized to our many different lifestyles, our teeth have become modified to enable us to make the most out of our resources, that is, to obtain food more efficiently and to extract nutrients more quickly and thoroughly. Teeth stab, crush, grind, slice, and chop food in hundreds of different ways. They are also used as weapons in defense against predators and in fighting members of one's own species. Their diversity of uses is reflected in their morphology.
Teeth are important to students of mammals in a number of contexts.
With practise, we can look at the teeth of an unknown mammal and make a very good guess about what it eats, even without seeing any other part of its body. Yet, while the teeth of different species are often specialized in different ways, teeth vary relatively little within most species. For this reason, they provide a wealth of information to the systematist. And teeth are extremely hard, the hardest part of the mammalian body. They fossilize more consistently than any other part of a mammal, and indeed many species of extinct mammals are known only from their teeth.