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.

Three-dimensional buccal-occlusal and occlusal reconstructions of two carnivoran tooth rows (red fox and giant panda) and two rodent tooth rows (golden-bellied water rat and Rothschild’s woolly rat) for the GIS analysis. Determination of surface orientation (orientation indicated by colour as shown on the colour wheel) allows the measurement of OPC (the number of coloured patches is indicated under each figure). These measures are compared with diets (carnivorous and herbivorous). 

Tooth complexity (measured as OPC) for five major dietary types in two taxonomically disparate groups (carnivorans (open boxes) and rodents (filled boxes)) for the lower (a) and upper (b) tooth rows. There is a consistent increase in the dental complexity when moving from hypercarnivory (meat-feeding) through animal-dominated (A-D) and plant-dominated (P-D) omnivory (meat and plants) to herbivory (plant material such as leaves and grasses). For several of the dietary categories, a similar range of values is found in both carnivorans and rodents (for example ‘herbivores’ in the lower tooth row and ‘carnivores’ in the upper tooth row).