New research by an international team of palaeontologists shows that the roughness of tooth surfaces can reveal important clues about what an animal has been eating.
Cichlid fish teeth. Smoother teeth at top have scraped algae from plants; the rougher teeth bottom row are from a rock-scraping species.
The study, published in the Royal Society journal Interface, reveals that there is a close match between roughness of teeth and diet, with teeth from animals that eat hard foods having rougher surfaces than those that eat soft foods.
The methods could also be used to investigate the diets of extinct animals such as giant marine reptiles and dinosaurs.
Gut contents are often used to study diet, but this only shows the contents of an animal's last meal. In contrast, tooth wear can provide information about what an animal normally eats.
'To our surprise, we found that in some cases tooth roughness is a more reliable guide to diet than looking in a fish's stomach,' explains Ole Seehausen from the University of Bern.
But before the researchers could understand how useful roughness might be as an indicator of diet, they first had to understand exactly what roughness is.
'This is tricky to measure,' says Mark Purnell, Professor of Palaeobiology at the University of Leicester. 'Smooth and rough surfaces are intuitively easy to distinguish, but is tree bark rougher than a road surface? Is the microscopic surface of chalk rougher than cheese? It's hard to make the comparison.'
'Engineers have been working on ways to measure roughness for decades. International standards are now being developed, based on new ways of measuring surfaces very precisely using special 3-D microscopes, and it is this approach that has been applied to the teeth in this study,' Purnell explains.
The strange 'throat teeth' of the cichlid fish Astatoreochromis alluaudi. The contoured surfaces at the bottom (140 micrometers across) show the difference between those that eat hard food (right) and those that don't (left).
The methods provide a useful new way of investigating fish diets – for example how changes in diet control the disappearance of species, or the evolution of new ones – and will be especially useful in analysis of fossils, the diets of which are hard to determine.
'It's most useful for looking at whether different species or individuals have been eating the same stuff as one another. For example, we're using the method to investigate feeding in fossil species that have all been interpreted as having the same diet because they have similar teeth and jaws. So we will be able to determine that extinct species ate different things to one another when we previously thought they ate the same food.'
The technique can't yet reveal exactly what an animal has been eating though.
'It's hard to link particular foods with particular roughness values,' explains Purnell. 'That might be possible for certain foods, but we're not there yet.'