An exquisite fossil alleged to be 515 million years old shows a compound eye so complex, it looks as good as any modern insect’s eye. The eye belonged to Anomalocaris, the fearsome predator of Cambrian seas, one of the key players in the Cambrian explosion – the sudden appearance of all the animal phyla in the earliest rock layers.
The discovery was announced in Nature.1 Previous fossils of Anomalocaris did not show clearly the structure of the eye. Paterson et al. found samples in South Australia with exquisitely preserved impressions in rock, so clearly defined that individual lens facets (ommatidia) could be studied for their optical properties. They counted 16,000 ommatidia in these eyes, compared to 3,000 for modern houseflies and 28,000 for dragonflies (the modern insects with the sharpest vision). The complete eyes were 2-3 cm across on this swimming shrimp-like arthropod that grew as large as 2 meters. Their arrangement on stalks protruding from the body provided excellent vision probably over a 360° field of view.
As with pixels in a camera, the more ommatidia, the better the image quality. In New Scientist, Paterson was quoted as saying that “Anomalocaris had remarkable vision, rivalling or exceeding that of most living insects and crustaceans … Very few modern animals, particularly arthropods, have eyes as sophisticated as this.” It would be impossible to modernize these modern eyes. PhysOrg included a photo of the rock impression showing the detailed lenses, while Live Science shows what the creature looked like. The Illustra Film Darwin’s Dilemma opens with animations of this amazing hunter and swimmer in action.
The authors promised to discuss “the origin of compound eyes.” Did they deliver? The reader can judge whether this statement in abstract answers the question:
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 with other evidence that these animals were highly mobile visual predators in the water column. The existence of large, macrophagous nektonic predators possessing sharp vision—such as Anomalocaris—within the early Cambrian ecosystem probably helped to accelerate the escalatory ‘arms race’ that began over half a billion years ago….
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