Coevolution has long been considered a major force leading to the adaptive radiation and diversification of insects and plants. A fundamental aspect of coevolution is that adaptations and counteradaptations interlace in time. A discordant origin of traits long before or after the origin of the putative coevolutionary selective pressure must be attributed to other evolutionary processes. Despite the importance of this distinction to our understanding of coevolution, the macroevolutionary tempo of innovation in plant defenses and insect counterdefenses has not been documented. Molecular clocks for a lineage of chrysomelid beetles of the genus Blepharida and their Burseraceae hosts were independently calibrated. Results show that these plants' defenses and the insect's counterdefensive feeding traits evolved roughly in synchrony, providing macroevolutionary confirmation of synchronous plant¿herbivore coadaptation. The association between these two groups of organisms was determined to be about 112 million years old, the oldest age so far for a specialized plant¿herbivore association.