DEVELOPING ECOMETRICS VIA MIDDLE TRUNK VERTEBRAL MORPHOLOGY IN NORTH AMERICAN SNAKES

Anthropogenic environmental change threatens to overwhelm the ability of ecosystems and species to sustain historical function. Integrative science merging the fields of paleontology, Earth sciences, and conservation biology is imperative to securing the future of Earth’s organisms, resources, and natural systems. Ecometrics – the community-level study of functional traits exhibiting quantifiable relationships with environmental gradients or climate – synthesizes modern, historical, and paleontological data across space and time for a plethora of organisms. Snakes are good candidates to expand ecometric research as ectotherms that have shown significant reactions to changes in the environment. Snakes use their vertebrae to locomote and interact with the environment, making vertebral shape a good element to investigate trait-environment relationships through deep time. We used geometric morphometrics to quantify anterior shape of middle trunk vertebrae with 23 homologous landmarks. We used generalized procrustes superimposition and a PCA to extract shape scores for 118 extant snake species from the continental United States and Canada. We tested differences between vertebral shape and ecological categories (fossorial, semifossorial, arboreal, semiarboreal, aquatic, semiaquatic, or terrestrial) and found that five of the first six PCs showed a significant difference between shapes for at least one ecological category (P < 0.01). Relative neural spine height (PC1; R² = 0.35), vertebral height-to-width ratio (PC2; R² = 0.22), relative neural canal size (PC3; R² = 0.13), relative prezygapophyseal facet length (PC5; R² = 0.21), and relative parapophysis length (PC6; R² = 0.22) explain ~86% of the shape variance and separate by ecological category. Our ecometric analysis suggests that relative neural spine height and relative neural canal size, vertebral height-to-width ratio, and relative parapophysis length are proxies for vegetation cover, annual precipitation, and mean annual temperature, respectively. These newly described ecometrics contribute to the toolbox of paleontological proxies to help interpret past climates and environments and assess community assembly through time.