First Author

In studying mammalian evolution, teeth are a scientist's most valuable fossil find. Alistair Evans, a postdoc at the University of Helsinki's Institute of Biotechnology in Finland, and his collaborators applied geographic information system (GIS) data-analysis tools to the dental landscape. GIS is typically used to analyse geographically referenced data — often obtained from aerial photography or satellite imagery. By analysing a three-dimensional image of an entire row of teeth, rather than comparing individual teeth, Evans and his colleagues were able to estimate an organism's entire food-processing capacity. On page 78 they detail similarities among 81 species of carnivorans and rodents. So what dictates this similarity?

Why have exhaustive quantitative comparisons of tooth shapes not been done before?

Analysis has previously been limited to more straightforward measurements such as individual tooth and crest sizes. Usually, techniques compare aspects of tooth shape that are homologous between species. We've tried to develop a technique that circumvents the need to look at similar teeth by analysing tooth shape as a whole.

This is not a typical use of GIS. What made you think of using it?

When you spend so long looking at teeth, you start to see shapes of mountains, valleys, hills and crests. Many tools used in geology and geography can be directly applied to other shapes, including those of teeth.

You revealed a surprising similarity between the groups — how can this be explained?

We measured dental complexity as a function of the number of features on teeth, such as cusps and blades of many possible shapes. A herbivorous animal has more complex teeth than a strict carnivore. But surprisingly, the range of complexity values recorded for four of the five diet types studied — the exception being sole meat-eaters — were very similar between the two taxonomic groups. There seem to be some scale-independent and phylogeny-independent forces that dictate complexity of tooth shape depending on diet. What you are eating is much more important to tooth complexity than your genetic heritage.

What's next?

We plan to apply this technique to other species. We'd like to study multituberculates — a major branch of mammals that became extinct after having thrived for 100 million years. With no living relatives and no idea what they ate, this is a group that people have been trying to interpret for a long time.