Meeting Abstract
Climate is known to influence body size in living reptiles. However, this relationship has not been investigated over geologic time intervals, nor compared among higher-order groups of extinct reptiles. Here I test the hypothesis that body size range undergoes holistic, synchronized change in lizards and crocodylians in response to climatic transitions over geologic time scales. I estimate snout-vent length (SVL) in lizards and crocodylians from intermontane basins in the Western Interior of North America through the Paleogene (66-23 million years ago), spanning several warming and cooling periods. The range of SVL increases in both lizards and crocodylians in the early Eocene. Maximum SVL increases 4X in lizards relative to the middle Paleocene (150 mm vs. 600 mm) and doubles in crocodylians (1 meter vs. 2 meters) and remains elevated through the Eocene. Meanwhile, minimum SVL remains consistent through the Paleogene in both groups (approximately 100 mm in lizards, 200 mm in crocodylians). This pattern is observed with no consistent latitudinal gradient across intermontane basin communities through the Paleogene. The observed changes in maximum SVL correspond to changes in mean annual paleotemperature in the Western Interior through the Paleogene. These results suggest that climatic changes may drive overall body size changes in lizards and crocodylians over deep time scales.
