Exquisitely preserved fossils left behind by creatures living more than half a billion years ago reveal in great detail identical structures that researchers have long hypothesized must have contributed to the archetypal brain that has been inherited by all arthropods. Arthropods are the most diverse and species-rich taxonomic group of animals and include insects, crustaceans, spiders and scorpions, as well as other, less familiar lineages such as millipedes and centipedes.