| Description |
Recent paleontological discoveries reveal a dramatic range of tooth morphologies in extinct reptiles, with some dentitions rivaling the complexity of extant mammals. Many of these dental morphologies have no modern analogs, inhibiting detailed dietary and ecological reconstructions for ancient ecosystems. Living saurian reptiles exhibit a wide range of diets, from carnivores to strict herbivores. Previous research suggests that the tooth shape in some lizard clades correlates with diet, but this has not been tested using quantitative methods. In order to elucidate the diet of extinct heterodont reptiles, I investigated the correlation between phenotypic tooth complexity and diet in living reptiles by examining the entire dentary tooth row in over 80 specimens comprising all major dentigerous saurian clades. I quantified dental complexity using orientation patch count rotated (OPCR), which does not require the identification of homologous landmarks on each tooth and discriminates diet in living and extinct mammals, where OPCR values increase with the proportion of dietary plant matter. OPCR was calculated from high-resolution CT scans, and I standardized OPCR values by the total number of teeth to account for differences in tooth count across taxa. In living saurians, OPCR values for omnivores and herbivores are higher than those of carnivores. In contrast with extant mammals, there appears to be greater overlap in tooth complexity values across dietary groups because multicusped teeth characterize herbivores, omnivores, and insectivores, and because the herbivorous skinks have particularly simple teeth. Additionally, insectivorous lizards have dental complexities that overlap with omnivores. These results suggest reptilian tooth complexity is related to diet, similar to extinct and extant mammals. These data were used to reconstruct the diet of 14 extinct crocodyliforms. OPCR data indicate that extinct crocodyliforms occupied a larger ecological range than their living relatives. In particular, herbivory independently developed at least three times, with each occasion utilizing a different tooth morphology to break down plant material. These data, when combined with key morphological characters, allow for the dietary ecology of extinct organisms to be reconstructed. |
