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The Eyes of Anomalocaris

The lord and master of the Cambrian seas was the undulating predator Anomalocaris. It was likely highly efficient, and now we are learning, highly visual. It was considerably larger than any other creature in those shallow seas and must have evoked fear with nothing more than its shadow.

Carnivory and predation were two key elements ushering in evolution and this generally requires vision as a principal sensory input. Sure enough, Anomalocaris had two eyes on stalks probably giving it a wide visual field. But, until recently, we have known very little about its visual capabilities and mechanisms. That has changed.

In a well-considered manuscript, Paterson et al describes fossils of the eye of Anomalocaris. From this work we now know that that this magnificent animal, probably the first in the line of apex predators of these shallow seas, had a compound eye that, in many ways, resembled the eye of today’s dragonfly.  Anomalocaris had perhaps as many as 16,000 hexagonal facets (individual units of the eye called ommatidia) in each eye and probably good vision. For reference, extant dragonflies have approximately 25,000 ommatidia and surprisingly good vision. Although I doubt that this Anomalocaris had vision good to read the newspaper, its vision would have been very good, at least in bright light. Its compound eyes were likely of the simplest and most common design—the apposition compound eye. This eye would require a great deal of light, and restrict the animal to a diurnal lifestyle. It would have been restricted to the rather bright light environments such as those found in a coral reef of today.  Almost certainly Anomalocaris would have had a wide field of vision and surprisingly sharp vision for smaller prey—just like a dragonfly.

With its anterior “arms” for capture and its mouth located beneath the proximal portion of its body, this first top predator would have had few competitors. Its prey species were soft bodied as it was as well. Such predation would inevitably drive the predator-prey “arms race” and could well have been instrumental as the stimulus for the evolution of hard shell-like bodies.

With Permission of the Royal Ontario Museum and Parks Canada © ROM-Photo Credit: J.B. Caron.

Paterson JR, Barcia-Bellido DC, Lee, MSY, et al:  Acute vision in the giant Cambrian predator Anomalocaris and the origin of compound eyes. Nature 2011; 480:  237-240.