How can we work out what a fossil mammal ate? Because the different foods that mammals eat vary so dramatically, from meat to grass, the teeth that they use to break them down are also diverse. One aspect that is highly variable in mammal teeth is how complex they are. We investigated the links between diet and dental complexity in mammals. Dental complexity is any measure of the number of features or faces on a 3D tooth surface, such as the number of patches on an orientation map of the surface - what you might call a compass map. We expected that the dental complexity of a species would be related to its diet, where species consuming a diet that needs lots of mechanical processing, such as plants, will have a much higher dental complexity than those that require less, namely vertebrate flesh. 

We confirmed this pattern when we compared carnivorans (including cats, dogs and pandas) and rodents (many species of mice and rats). Both groups show a clear trend of increasing dental complexity from meat-eater through omnivores to plant-eaters (Evans et al. 2007). Unexpectedly, the herbivorous rodents showed the same dental complexity as the herbivorous carnivorans, and there was a similar correspondence between carnivorans and rodents for other trophic levels. 

Dental complexity is a high-level indicator of diet that is scale- and phylogeny-independent that has not been achieved before – in other words, we are able to compare apples and oranges, and tell you what you ate, regardless of how big you are or who you are related to. This is particularly useful for interpreting diets for groups that are wholly extinct and have no living analogues.