A preeminent association between flowering plants and insects is pollination. Pollination is a mutualism in which two interactors reciprocally benefit: a host plant receives the service of insect pollination in return for a reward provided for its insect pollinator. Typically, the reward is nectar or pollen, but occasionally the provision can be a mating site, resin for nest construction, floral aroma, or even the attraction of plant-generated heat. Evidence from the fossil record and from the inferred ecological and phylogenetic relationships between flowering plants (angiosperms) and their insect pollinators indicates that these types of associations initially were launched during the Early Cretaceous, 125–90 million years ago. It was from this interval of time that flowering plants experienced their initial radiation, as did major groups of insects, especially Thysanoptera (thrips), Coleoptera (beetles), Diptera (flies), Lepidoptera (moths and butterflies), and Hymenoptera (sawflies, wasps, ants, and bees). However, until recently, very little was known about more ancient modes of insect pollination, those that predated the appearance of flowering plants or that occurred before angiosperms became dominant in terrestrial ecosystems.