INSECT DIVERSITY IN THE FOSSIL RECORD

Insects possess a surprisingly extensive fossil record. Compilation of the geochronologic ranges of insect families demonstrates that their diversity exceeds that of preserved vertebrate tetrapods through 91 pe rcent of their evolutionary history. The great diversity of insects wa s achieved not by high origination rates but rather by low extinction rates comparable to the low rates of slowly evolving marine invertebra te groups. The great radiation of modern insects began 245 million yea rs ago and was not accelerated by the expansion of angiosperms during the Cretaceous period. The basic trophic machinery of insects was in p lace nearly 100 million years before angiosperms appeared in the fossi l record.