Meeting Abstract
Discerning the role of constraints and functional conservatism in the presence of static character evolution is a central problem in evolutionary morphology. Differentiating these scenarios is impossible without a synthesis of evolutionary history with anatomical, functional, and ecological data. Here, we use a clade level approach to structure-function relationships, comparative biomechanics, and detailed myology of extreme test cases to reveal the complex functional capabilities of an otherwise seemingly constrained set of evolving characters in rodents. The simplicity of rodent gnawing dentition allows for an enormous range of dietary/functional specializations without qualitative structural anatomical changes, and independent evolutions of superficially similar masseter arrangements do not correlate with similar functions. Further, the only major changes to the mostly static Eocene-age masseter arrangements in recent rodent evolution are found to occur independently in the most derived ricochetal rodents that lose much of their temporalis musculature, but not in myomorphic ricochetal rodents with preexisting complex anterior masseter arrangements. This latter result independently validates our comparative biomechanic findings that the myomorphic masseter arrangement replaces temporalis functions generally, creating a unique mammalian masticatory system. These data demonstrate that complex existing functional capabilities can underlie morphological stasis and that stasis need not indicate morphological constraint or functional conservatism.
