Repeated Evolution of Herbivorous Crocodyliforms during the Age of Dinosaurs

Abstract

Extinct crocodyliforms from the age of dinosaurs (Mesozoic Era) display an impressive range of skeletal morphologies, suggesting a diversity of ecological roles not found in living representatives [1-6]. In particular, unusual dental morphologies develop repeatedly through the evolutionary history of this group [2, 4-9]. Recent descriptions of fossil crocodyliforms and their unusual teeth provide the inferential basis for a wide range of feeding ecologies. However, tests of these hypotheses are hindered by the lack of directly comparable dental morphologies in living reptiles and mammals, thereby preventing an accurate ecosystem reconstruction. Here, we demonstrate, using a combination of the orientation patch count rotated method and discrete morphological features, that Mesozoic crocodyliforms exploited a much greater range of feeding ecologies than their extant relatives, including likely omnivores and herbivores. These results also indicate that crocodyliforms independently developed high-complexity dentitions a minimum of three times. Some taxa possess teeth that surpass the complexities of living herbivorous lizards and rival those of omnivorous and herbivorous mammals. This study indicates that herbivorous crocodyliforms were more common than previously thought and were present throughout the Mesozoic and on most continents. The occurrence of multiple origins of complex dentitions throughout Crocodyliformes indicates that herbivory was a beneficial dietary strategy and not a unique occurrence. Many of these crocodyliforms lived alongside omnivorous or herbivorous synapsids, illustrating an ecological partition that is not observed today.

Keywords: dental complexity; diet; mesozoic; paleoecology.