This past month, I was part of a group of people who published a paper looking at how diapsids (that is, lizards, snakes, crocodiles, dinosaurs, birds, etc) change – or don’t change – the number of teeth they have as they grow up and age. We used a dataset of American alligators (Alligator mississippiensis), salt water crocodiles (Crocodylus porosus), and komodo dragons (Varanus komodoensis) that documented their jaw lengths and how many teeth each jaw had in it. Overall, we found that in all of these species they had the same number of teeth as babies that they did when they were adults. For some of them, such as the American Alligator, this was despite a huge change in body size; the smallest alligator skull was 3.5 cm long, while the biggest was almost 70 cm long.
From a palaeontological point of view, these sorts of results help us understand the type and form of variation we might expect in the fossil record. One character that is often used in palaeontology to differentiate between two species is the number of teeth each of them might have. However, there has been some debate as to how reliable this characteristic might be. Our research suggests that using the number of teeth to split apart, or in the case of babies and adults, group together two different specimens is a not a bad idea. Still though, the story is far from done, as some of the additional information that we gleaned after accumulating a large body of literature on other animals showed that the relationship is not totally cut and dried. For example, smaller species of lizards do appear to increase the number of teeth they have during their lifetime, while there is some limited evidence in a couple of large-bodied theropods that they might decrease their tooth count as they grow. In the end though, having a question that is partially answered, but gives you a lot more work to do is a generally a good thing in science. Go collect more specimens, more data, and do it all again.
Brown, C.M., C.S. VanBuren, D.W. Larson, K.S. Brink, N.E. Campione, M.J. Vavrek, and D.C. Evans. 2015. Tooth counts through growth in diapsid reptiles: Implications for interpreting individual and size-related variation in the fossil record. Journal of Anatomy(Advanced early online publication).