The compound eye of a trilobite

The compound eye of a trilobite

Trilobites appeared after the Cambrian boundary, and possessed the first eyes of the fossil record. Interestingly, trilobite eyes used the mineral calcite as a lens—a structure that no living animal has.

Photo: Wikicommons, http://commons.wikimedia.org/wiki/Image:Paralejurus-Compound-eye.jpg