What is the Evolutionary History of Insects?
The evolutionary history of insects, like that of many other invertebrate groups, is poorly understood. For many decades, it was thought that they branched off of millipedes and centipedes, which are known to have colonized the land as early as 428 million years ago, during the Silurian period. But recent genetic studies suggest that insects more likely split off from crustaceans sometime around 410 million years ago. The circumstances of this evolutionary change are subject to debate, and much less clear than the evolution of lobe-finned fish into primitive tetrapods. The earliest known specimen in the history of insects is the Devonian fossil Rhyniognatha hirsti, dated to between 396 and 407 million years ago. It was found in the Rhynie Chert formation, a well-preserved Devonian ecosystem which includes some of the first land plants with vascular tissues and among the earliest and best preserved fossils of terrestrial arthropods. The mandibles of this insect suggest that it had alrea
