The practice of designating state symbols is a way for a commonwealth to celebrate its unique natural, cultural, and historical heritage. These symbols often reflect what the region values most, from its state bird to its official flower. The state fossil acts as a tangible marker of immense geological time, recording the life and environment of a distant past. Pennsylvania’s choice tells a specific story about the ancient seas that once covered the land.
The Identity of the State Fossil
Pennsylvania’s official state fossil is the trilobite known as Phacops rana. This scientific name identifies a member of an extinct group of marine arthropods, distant relatives of modern crustaceans, spiders, and insects. The name Phacops rana translates literally to “frog eyes,” a reference to the organism’s distinctive feature.
The fossil is recognized by its three-lobed body structure, which gives the trilobite group its name, and its large, compound eyes. These eyes were composed of many individual lenses, a complex optical system known as a schizochroal eye. While the original legislative act used Phacops rana, the species is sometimes referred to by the updated scientific classification, Eldredgeops rana.
Geological Significance and Habitat
This ancient creature existed during the Middle Devonian Period, roughly 393 to 383 million years ago. During this era, the area that would eventually become Pennsylvania was submerged beneath a warm, shallow sea. The trilobite thrived in this marine environment, making its fossilized remains common in the state’s sedimentary rock layers.
The fossil is particularly abundant in Devonian-age rocks found across central Pennsylvania, such as the Mahantango Formation. These rocks represent the ancient seabed where the trilobite lived, died, and was preserved. Phacops rana could grow up to six inches long, a relatively large size for a trilobite.
When threatened, this marine animal had the ability to protect itself by rolling its body into a tight ball, a defensive posture known as volvation. This behavior explains why many specimens are found preserved in a coiled position, with their hard exoskeleton facing outward. The presence of Phacops rana fossils helps geologists date the rock strata where they are found, making it a useful indicator of the Devonian time period.
The fact that the trilobite had to periodically shed its exoskeleton to grow also contributed to the fossil record. Each individual could leave behind multiple carapaces, or shed shells, throughout its lifespan, significantly increasing the chances of fossilization. Because of this, even partial fragments of the trilobite are frequently discovered in the state’s Paleozoic rocks.
The Official Designation Process
The formal recognition of Phacops rana as the state fossil occurred when the Pennsylvania General Assembly passed Act No. 138. The designation became official on December 5, 1988, following a legislative effort that brought the ancient creature into the modern spotlight. The process was propelled by a campaign initiated by an elementary school science class.
Students and amateur paleontologists often champion such designations to celebrate local geological heritage and promote science education. The legislative act specifically cited the trilobite’s wide distribution and common occurrence across the state as the reason for its selection. This abundance made it a representative symbol of Pennsylvania’s deep geological history.
The bill that formalized the designation was introduced into the House, passing into law and amending the Pennsylvania Statutes. This legal action solidified the trilobite’s place among the state’s other official emblems. The selection of a marine invertebrate highlights the state’s deep connections to the ancient sea that once shaped its foundation.