Meeting Abstract
Patterning of the vertebrate dentition is an extensively studied topic in the fields of palaeontology and developmental biology. It is well known that animals with continuous tooth replacement (polyphyodonty) replace their teeth in distinct waves around the mouth, the timing of which is predictable over long time periods. The slowing of tooth replacement in the synapsid lineage has been posited as one of the key mechanisms in the evolution of diphyodont (one replacement) heterodont dentitions from polyphyodont, homodont ancestors. As most studies on the patterning and timing of polyphyodonty have focused on homodont animals, the relationship between tooth size and shape and wave replacement patterns is unknown. Using historical x-ray data of polyphyodont homodont (Iguana, n=12) and heterodont reptiles [Dracaena (n=2), Varanus (n=3), Teius (n=2), and Alligator (n=2)] collected monthly for up to two years, the timing of tooth development versus tooth replacement can be determined. Results in all animals show normal, predictable wave replacement patterns in the dentition. In the homodont Iguana, the timing of tooth development and tooth replacement is tightly correlated. However, in the heterodont reptiles, the developmental time is different between teeth: smaller teeth take one or two months to develop before eruption, while larger teeth take up to five months. Additionally, replacement waves slow throughout the life of the animal as teeth get larger with subsequent replacements. The results of this study in reptilian model organisms suggest that larger, more complex teeth take more time to develop than smaller, simple teeth in the same jaw. Therefore, the slowing of tooth replacement over evolutionary time is likely a key mechanism in the development of heterodont dentitions.
