Geologic History

Phacops rana is one of the most common trilobites found in the Middle Devonian of North America. It can be recognized by its large eyes and segmented thorax (middle portion). They are, in fact, the first organisms on earth known to have developed eyes. The trilobites had compound eyes, composed of many individual lenses, like those of insects. Trilobites possess the most ancient visual system known to scientists and thus they provided some of the best direct evidence of eye evolution.

Author’s collection – trilobite (Devonian Windom Shale, Moscow Formation – Western New York)

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