Extreme and rapid bursts of functional adaptations shape bite force in amniotes

Abstract

Adaptation is the fundamental driver of functional and biomechanical evolution and can be linked to rates of phenotypic trait evolution. Significant shifts in evolutionary rates are seen as instances of exceptional adaptation. However, whether or not signatures of exceptional adaptations (elevated rates) can be distinguished from general adaptations (background rate) in biomechanical traits remains to be tested in a robust statistical framework. Here, we apply a recently developed phylogenetic statistical approach for detecting exceptional adaptations in bite force, in a large group of terrestrial vertebrates, the amniotes. Our results show that bite force in amniotes evolved through multiple bursts of exceptional changes, whereby whole groups - including Darwin';s finches, maniraptoran dinosaurs (group of non-avian dinosaurs including birds), anthropoids and hominins (the group of species including modern humans) - experienced significant rate increases compared to the background rate. However, in most parts of the amniote tree of life we find no exceptional rate increases, indicating that coevolution with body size was primarily responsible for the patterns observed in bite force. Our approach represents a template for future studies in functional morphology and biomechanics, where exceptional functional adaptations can be quantified and potentially linked to specific ecological factors underpinning major evolutionary radiations.