Acute vision in the giant Cambrian predator Anomalocaris and the origin of compound eyes

New fossils from Australia reveal that the Cambrian apex predator Anomalocaris possessed compound eyes more powerful than those of most living arthropods. A sharp-eyed Cambrian predator The metre-long swimming invertebrate Anomalocaris was the top predator in the Cambrian ocean more than 500 million years ago. Recent discoveries of fly-like compound eyes attributable to this creature confirm suggestions that it is related to the arthropods — jointed-limbed creatures such as insects, crustaceans and trilobites — and show that compound eyes evolved before hardened exoskeletons. The superbly preserved fossils from South Australia show that Anomalocaris had exceptional vision. Its compound eyes are among the largest and most acute to have ever existed; each eye is up to 3 centimetres long and contains more than 16,000 lenses. The existence of highly visual hunters during the Cambrian would have accelerated the pace of the predator–prey 'arms race' then under way. Until recently 1 , intricate details of the optical design of non-biomineralized arthropod eyes remained elusive in Cambrian Burgess-Shale-type deposits, despite exceptional preservation of soft-part anatomy in such Konservat-Lagerstätten 2 , 3 . The structure and development of ommatidia in arthropod compound eyes support a single origin some time before the latest common ancestor of crown-group arthropods 4 , but the appearance of compound eyes in the arthropod stem group has been poorly constrained in the absence of adequate fossils. Here we report 2–3-cm paired eyes from the early Cambrian (approximately 515 million years old) Emu Bay Shale of South Australia, assigned to the Cambrian apex predator Anomalocaris . Their preserved visual surfaces are composed of at least 16,000 hexagonally packed ommatidial lenses (in a single eye), rivalling the most acute compound eyes in modern arthropods. The specimens show two distinct taphonomic modes, preserved as iron oxide (after pyrite) and calcium phosphate, demonstrating that disparate styles of early diagenetic mineralization can replicate the same type of extracellular tissue (that is, cuticle) within a single Burgess-Shale-type deposit. These fossils also provide compelling evidence for the arthropod affinities of anomalocaridids, push the origin of compound eyes deeper down the arthropod stem lineage, and indicate that the compound eye evolved before such features as a hardened exoskeleton. The inferred acuity of the anomalocaridid eye is consistent