Phacops rana Trilobite

This November we show off this complete Phacops rana trilobite. I collected this Phacops rana (also known as Eldredgeops rana) roughly thirty years ago at the current site of Penn Dixie Fossil Park in Hamburg, New York before the Hamburg Natural History Society had purchased the land in 1995.

Phacops rana is a species of trilobite from the Devonian period (~390 million years ago) that is most commonly found in the northeast US, Ontario and Morocco. Rana is Latin for “frog” and the Greek root, fakos, means “lens” as the bulbous eyes of these trilobites have a strong resemblance to those of frogs. Their highly sophisticated eyes had calcite lenses, depth perception, color perception and were able to swivel 360° allowing them to always be on the lookout for potential predators. Not only did these advanced eyes survey for danger, but they also are an indicator of the predatory nature of Phacops rana as they probably spent most of their lives on the ocean floor eating other smaller aquatic animals and larvae. These trilobites could grow between .5 inches to over 4 inches long, making them some of the largest arthropods of their time.

The glabella (or nose-like part) acted as part of their digestive system and was large with many bumps. This feature as well as their schizochroal eyes make the Phacops rana one of the most recognizable trilobites. Its head (the cephalon), thorax, and tail (pygidium) are fairly rounded and plain. Like present-day horseshoe crabs, as Phacops grew it would molt its exoskeleton. When it felt threatened, it would roll up into a tight ball using its tough exoskeleton as protection, sometimes accidentally burying itself alive under sediment and becoming fossilized. 

This particular specimen is roughly 1.75 inches long x 1.26 inches wide with well-defined schizochroal eyes clearly showing the larger cornea lenses separated by sclera tissue. The small bumps on the glabella are apparent as well as the long central axial lobe and the rib-looking pleural lobes to the right and left of the axial lobe. 


Phacops rana (Eldredgeops rana)
Middle Devonian
Windom Shale
Hamburg, New York