PLANT-INSECT ASSOCIATIONS OF THE MID MESOZOIC

Recent discoveries from the Late Triassic to Early Cretaceous of South Africa and northern Eurasia now indicate that insect herbivores and pollinators were targeting a variety of ferns and gymnospermous seed plants in novel and diverse ways. During the Late Triassic (Carnian, ca. 225 Ma), a major radiation of insect endophytic herbivores, following the end-Permian crisis, have been documented for the Molteno Formation of the Karoo Basin. The monospecific consumption of particular plant species, organs and tissues by herbivore specialists is analogous to the colonization of angiosperms by a more modern spectrum of insect herbivores about 100 million years later. From the late Middle Jurassic (Bathonian–Callovian boundary, ca. 165 Ma), additional evidence for diverse associations is recorded from the Jiulongshan Formation of Inner Mongolia, in northeastern China. In these deposits, as in the Molteno Biome, a considerable amount of external foliage feeding, piercing-and-sucking, oviposition, leaf mining, galling, seed predation, wood boring and pollinator activity characterize a highly diverse flora consisting of cycads, ginkgophytes, bennettitaleans, pentoxylaleans, seed-ferns, and gnetophytes. These activities occurred in lakeshore woodland environments and represent a major diversification on extinct plant clades of insect basal lineages that remain today. By the mid Early Cretaceous (late Barremian, ca. 125 Ma), there is an extension of insect herbivory and pollination associations that are indicated by the Yixian Formation in Liaoning, northeastern China. This deposit signals one of the earliest known floras harboring a few basal angiosperm taxa, but is overwhelmingly dominated by ferns and gymnosperms, where virtually all of the herbivore and pollinator activity resided. Interestingly, although this flora was diverse and contains such specialized associations as beetle leaf mines on the broadleaved conifer Liaoningocladus and globular galls on bennettitalean foliage, it nevertheless represents a reduction of herbivorous associations from Middle Jurassic times. These three, mid Mesozoic deposits represent a significant heightening of plant–insect associational diversity from the Paleozoic and record levels ecologically equivalent to angiosperms and their insect herbivores and pollinators.