Pennsylvanian

The Pennsylvanian is the later subperiod of the Carboniferous, following the Mississippian and preceding the Permian. It spans roughly 323 to 299 million years ago. The corresponding rocks form the Pennsylvanian subsystem: a time interval and the rocks deposited during it are related but distinct uses of the name.^[ref]

The word is useful when comparing fossils from different regions. A fossil described as Pennsylvanian belongs to this interval rather than to an undifferentiated stretch of the Carboniferous. The classification provides a shared temporal framework; it does not imply that every locality had the same environment or preserved the same organisms.