A survey of biomechanically significant aspects of the jaw apparatus in 13 orders of recent and fossil ungulates indicates that an expanded angular process evolved independently at least 12 times. Temporal fossa size is reduced inmost ungulatesof modern aspect, but not in many early ungulates. Expansion of the masseter and internal pterygoid musculature (inferred from the expanded angular process) may represent an adaptation for enhanced control of grinding action in mastication.