Selection for divergent performance optima has been proposed as a central mechanism underlying adaptive radiation. Uncovering multiple optima requires identifying forms associated with different adaptive zones and linking those forms to performance.However, testing and modeling the performance of complex morphologies like the cranium is challenging. We introduce a three- Studies of morphological adaptation aim to link form (morphology) to biomechanical function, and biomechanical function to performance, or the ability to carry out ecological tasks that influence fitness (Arnold 1983). Selection for performance is thought to drive the evolution of underlying form. Implicit in many studies is the assumption of the existence of performance optima, or values of peak performance toward which lineages evolve. Many morphological systems contain multiple performance optima, each of which offers the opportunity to evolve into a dif- * These authors contributed equally to this work.