The story of flowers and insects is one of the best examples of co-evolution. The gut contents, wing structures, and mouthparts of fossilized beetles and flies suggest that they acted as early pollinators. The association between beetles and angiosperms during the Lower Cretaceous period led to parallel radiations of angiosperms and insects in the Upper Cretaceous. The evolution of in Upper Cretaceous flowers signals the beginning of the mutualism between hymenopterans and angiosperms.