Insect origination and extinction in the Phanerozoic

Abstract Insects (Superclass Hexapoda) are the most successful group of living terrestrial arthropods and the richness of their fossil record is only just beginning to be realized with the recent publication of two extensive databases. Hexapods first appeared in the Early Devonian, post-dating the Cambrian ‘explosion’ of marine arthropods by some 140 Ma. The earliest Hexapoda belong to primitively wingless taxa; however, these ‘Apterygota’ comprise less than 1% of all hexapod species. The appearance of winged insects (Pterygota) in the mid-Carboniferous was accompanied by a major adaptive radiation of non-holometabolous hexapods at ordinal level This was supplemented in the Permian by the radiation of insects with complete metamorphosis (Holometabola). The number of insect orders present in this period was similar to that at the present day. The family data suggest four major periods of origination in the Phanerozoic, with peaks in the Permo-Carboniferous, Early Jurassic, Early Cretaceous and Eocene. Unlike the Tertiary, the Palaeozoic and Cretaceous peaks are accompanied by considerable turnover of families; they are followed by reduced palaeodiversity in the Early Triassic and Late Cretaceous and Palaeocene. The former decline may be linked with the general extinction at the Permian/Triassic boundary and the latter with the rise of the angiospermous flowering plants. Insect generic data for the Phanerozoic reflect the pattern shown by families but not orders. In general, insect diversity may be explained by an overall trend towards low extinction and steady origination at a subordinal level since the Palaeozoic.