The Paleozoic Era saw the most dramatic biotic changes on earth. At the opening of the era (i.e., the beginning of the Cambrian, 543 mya) the biotic world experienced a literal explosion of diversity, all of it marine. During the "Cambrian Explosion" came the development of major animal body plans and the rapid proliferation of complex life (e.g., Conway Morris, 1979, 1989). By the end of the Paleozoic, life had invaded land - a littoral explosion of diversity, first by the plants, and shortly followed by arthropods and then other animals. Terrestrial ecosystems came into existence during the Paleozoic, which not only affected the surface of the earth but the atmosphere as well. For the story of insects, however, the latter half of the Paleozoic interests us. Land plants made their first appearance in the Ordovician (490-443 mya), and terrestrial arthropods migrated into these miniature plant communities during the later Silurian (443-414 mya), but the Silurian fauna as it is generally understood consisted entirely of primitive arachnids and myriapods (e.g., Jeram et al., 1990). Very soon thereafter were the first hexapods, which were undoubtedly already present by the end of this epoch (e.g., Engel and Grimaldi, 2004a). The Early Devonian (ca. 410 mya) heralded the first hexapods (at least the first preserved as fossils) and it was not long thereafter that insects dominated earth, becoming the first to fly and then rapidly proliferating during the Carboniferous and Permian. Owing to constant tectonic change of the earth since the Paleozoic, however, there are not as many terrestrial deposits with insects as there are from later eras.

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