Using Tooth Wear to Determine Diet in the Fossil Record

What types of food an extinct vertebrate ate millions of years ago seems like one of those things that would be difficult to know. And to a large extent, it is. Short of fossilized gut contents or dung that can be positively attributed to its maker, palaeontologists have no way of knowing with any certainty what an extinct vertebrate ate. Looking at the shapes of the teeth might help (is it an herbivore or a carnivore?), as might looking at the proportions of the hindlimbs (does it look like a fast-moving predator or a slow-moving grazer?). But those kinds of observations can only get us so far. Not surprisingly, palaeontologists have had to come up with some clever methods to probe a bit deeper.

      One of those methods is dental microwear analysis. This is a means by which palaeontologists look at microscopic pits and scratches on teeth, which are left as a result of feeding. We know from looking at the teeth of living vertebrates that the sizes, shapes, and proportions of those microscopic features correspond to diet. So, for example, a hoofed mammal with many coarse scratches on its teeth might be classified as a grass grazer, whereas a hoofed mammal with many pits and fine scratches on its teeth might have eaten fruits and leafy browse. By applying those same principles to the fossil record, we can come up with better ideas about the diets of extinct vertebrates (those with teeth, at least).

Above: Microwear features on the enamel surface of an elk molar (from Fraser et al., 2009). This animal is a mixed feeder (eating both grass and browse), as evidenced by the varied pits and scratches on its teeth.

      This method isn’t foolproof, of course. Dental microwear features can result from many factors besides food, including the presence of environmental grit, and behaviours like grooming, gnawing on non-food items, or tooth grinding. However, even some of those confounding factors can teach us something about the environment an animal might have lived in, and what food options might have been available to it. The interplay between food, jaw mechanics, and tooth wear continues to be an active area of research.

      Early dental microwear studies relied heavily on scanning electron microscopy. Researchers would take photomicrographs of tooth surfaces and tally the various pits and scratches by hand to get an idea of what a fossil animal might have eaten. This method has been adapted in recent years for use with simple light microscopy, but the principles remain the same. However, feature-counting has been criticized by some as being too time-consuming and observer-dependent. For this reason, numerous researchers now rely on confocal microscopy to produce 3D digital elevation models, which are then subjected to automated texture analysis techniques.

Above: 3D dental microwear image of a duck-billed dinosaur tooth. Based on the wide range of tooth wear features exhibited by these animals, they do not appear to have been picky eaters (Mallon and Anderson, 2014).
Further reading:

Fraser, D., Mallon, J. C., Furr, R., & Theodor, J. M. (2009). Improving the repeatability of low magnification microwear methods
      using high dynamic range imaging. Palaios, 24(12), 818-825.

Grine, F. E. (1986). Dental evidence for dietary differences in Australopithecus and Paranthropus: a quantitative analysis of
      permanent molar microwear. Journal of Human Evolution, 15(8), 783-822.

Mallon, J. C., & Anderson, J. S. (2014). The functional and palaeoecological implications of tooth morphology and wear for
      the megaherbivorous dinosaurs from the Dinosaur Park Formation (upper Campanian) of Alberta, Canada. PLOS ONE
      9(6): e98605. doi:10.1371/journal.pone.0098605

Scott, R. S., Ungar, P. S., Bergstrom, T. S., Brown, C. A., Childs, B. E., Teaford, M. F., & Walker, A. (2006). Dental microwear
      texture analysis: technical considerations. Journal of Human Evolution, 51(4), 339-349.

Solounias, N., & Semprebon, G. (2002). Advances in the reconstruction of ungulate ecomorphology with application to early
      fossil equids. American Museum Novitates, 1-49.

Ungar, P. S. (2015). Mammalian dental function and wear: A review. Biosurface and Biotribology, 1(1), 25-41.

Walker, A., Hoeck, H. N., & Perez, L. (1978). Microwear of mammalian teeth as an indicator of diet. Science, 201(4359),

Post by Jordan Mallon, Canadian Museum of Nature
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