What important development occurred at the end of the Pennsylvanian Epoch?

The Pennsylvanian is an epoch of the Carboniferous period lasting from roughly 325 Ma to 299 Ma (million years ago). As with most other geologic periods, the rock beds that define the period are well identified, but the exact date of the start and end are uncertain by a few million years. The Pennsylvanian is named after the state of Pennsylvania where rocks from this age are widespread.