A study of fossilized lampreys dating from more than 300 million years ago is challenging a long-held theory about the evolutionary origin of vertebrates. These ancient, jawless, eel-like fishes arose around half a billion years ago and they have long provided insights into vertebrate evolution. The analysis of the fossils counters the established view that the blind, filter-feeding larvae of modern lampreys (ammocoetes) are a holdover from the ancestors of living vertebrates.