Phacops rana

The fossil record of *Phacops rana* was extensively studied by paleontologist Niles Eldredge in the early 1970s. His research on the distinct changes in the number of lenses in the trilobite's compound eyes directly contributed to the formulation of the theory of punctuated equilibrium, which he co-authored with Stephen Jay Gould.

*Phacops rana* is an iconic marine arthropod from the Devonian period, often referred to as the "Age of Fishes," which occurred roughly 400 to 360 million years ago. Their fossils are primarily found in eastern North America, particularly in the ancient sedimentary rocks of regions like New York State and Ohio.

*Phacops rana* is notable for its exceptionally large, prominent compound eyes, which are often beautifully preserved in fossils. Each eye contained dozens of large, visible calcite lenses, and the structure of these schizochroal eyes provided the trilobite with a highly advanced, nearly 360-degree field of vision to spot predators on the ancient sea floor.

Yes, like many trilobites, *Phacops rana* possessed the ability to enroll, meaning it could curl its segmented body into a tight, defensive ball to protect its soft underbelly from predators. Many well-preserved *Phacops rana* fossils from the Devonian period are found completely enrolled, capturing this final defensive posture.