Functional dietary specialization and unique biomechanical trade-offs underpin phenotypic evolution in the snake jaw system

Morphological adaptations in the jaws of snakes directly enable many elements of their unique feeding ecology, including the ability to swallow large prey items whole. However, macroevolutionary trends between snake dietary ecology and jaw system morphology have yet to be investigated with dense sampling across a broad phylogenetic scale. We used computerized tomography data and phylogenetic comparative methods to explore the evolution of two functionally important jaw traits, relative quadrate length (RQL) and jaw-closing mechanical advantage (MA), across nearly 600 species of colubroid snakes. While relative prey bulk explained observed patterns of quadrate length evolution largely on its own, both relative prey bulk and relative prey mass influenced the evolution of mechanical advantage. Additionally, there was a weak but significant inverse relationship between RQL and MA. We suggest that selection for maintaining a large gape has largely co-opted the force-velocity trade-off to become the primary driver of jaw system evolution in snakes. Our results highlight the significance of macrostomy as an important innovation in the evolutionary history of snakes and provide new insights into the macroevolutionary relationship between ecology and phenotype in this diverse global radiation.