From Ancient to Modern
Many modern insect families and even some genera can trace their lineages deep into the Mesozoic or even the Paleozoic. The continuity between prehistoric and living insects is one of the most striking features of insect evolution — while individual species come and go, the basic body plans and ecological strategies of many insect groups have proven remarkably durable over hundreds of millions of years.
Living Fossils
Some modern insect groups have changed remarkably little from their prehistoric ancestors. Cockroaches, as illustrated by Archimylacris and Aphthoroblattina, had established their basic body plan by the Carboniferous and have retained it for over 300 million years. Dragonflies today are smaller than Meganeura but share the same fundamental wing design and predatory lifestyle. Silverfish and bristletails (Zygentoma and Archaeognatha) are wingless insects whose body plans have changed little since the Devonian.
Lineages That Survived Extinctions
The Permian-Triassic extinction destroyed several insect orders, but the lineages that survived — including the ancestors of modern beetles, flies, wasps, and bugs — went on to diversify enormously. The K-Pg extinction had less impact on insects, and most modern insect families were already established before the asteroid struck. The Green River Formation shows that by the Eocene, insect communities were recognizably modern in composition.
Key Transitions
Tracing specific lineages reveals key transitions: the evolution of ants from wasp ancestors (documented by Sphecomyrma), the independent evolution of eusociality in termites and ants, the development of beetle elytra from simpler wing modifications (compare Protelytroptera to modern beetles), and the gradual replacement of gymnosperm-pollinating insects (like Kalligrammatidae) by angiosperm-pollinating ones (bees, butterflies).
What Changed, What Didn't
What has changed most dramatically is size (insects are generally smaller now than in the Carboniferous), the composition of dominant groups (beetles, flies, and ants now dominate rather than palaeodictyopterans and griffinflies), and the ecological relationships with plants (shifted from gymnosperm to angiosperm partners). What has remained constant is the basic insect body plan (head, thorax, abdomen, six legs, usually wings), the fundamental respiratory system (tracheae), and the core ecological roles that insects play: herbivores, predators, detritivores, pollinators, and parasites.