| dc.description.abstract | Anthropogenic effects on the environment are an irrefutable actuality. Understanding how environmental changes affect organismal fitness, ecology, morphology, and evolution is critical for managing natural systems and conserving organisms through these changes. The study of morphological variation in skeletal elements provides an integrative route to bridge the gap between the past and the present of organism-environment interactions over long time scales. In this dissertation, I focus on snake morphological variation and its implications for taxonomy, phylogeny, ecology, and environmental change across space and time. I show that describing fossil snakes can be useful for understanding paleoenvironment, biogeography, and evolutionary patterns, epitomized by addressing a temporal gap for North American snakes, using vertebral morphology to identify taxa, and using proxy congenerics with climate data to estimate paleoclimate. The fossils and models support a hypothesis of gradual modernization in North American snakes occurring as Miocene environments grew drier and cooler in the Great Plains. I assess variation in snake middle trunk vertebrae with geometric morphometrics as a method for assigning snake vertebrae to taxon. Applying geometric morphometrics at multiple taxonomic levels indicated that a stepwise method may maximize the ability to identify snakes through vertebrae without diagnostic expertise. I demonstrate how combining external and skeletal morphological data with geographic, climatic, sex, and dietary data in the Western massasauga shows that morphological change within a species is better identified by combining the variation in both datasets, as variation gradated between the Southwest and Northeast. Finally, I construct a modern functional trait-environment framework for North American snakes using middle trunk vertebrae. I demonstrate that several aspects of shape variation are related to temperature-related variables and ecological province, and that combining multiple aspects produces better maximum likelihood models than any single aspect. My dissertation contributes to qualitative and quantitative methods to assess snakes and their interactions with the environment through time. This opens new avenues to append deep time data to our understanding of how snakes are functionally related to their environments, and what actions we can take to conserve and manage snakes in potential environmental futures. | |
