“Metamorphosed” Fern Fossil

Fern fossil bore witness to a continental collision.

Color photograph of the Rhode Island specimen of a Pecopteris sp. that was "metamorphosed" or streched by tectonic movement of rocks.
Identification: Pecopteris sp.
Common Name: Tree fern frond
Kingdom: Chlorobiota (Green Plants)
Phylum: Tracheophyta (Vascular Plants)
Class: Filicopsida (Ferns)
Order: Marattiales
Location: Rhode Island, United States
Rock Unit/Stratigraphy: Rhode Island Formation
Geologic Time Period: Carboniferous (Pennsylvanian)
Estimated age: Approximately 306 million years before present
Significance: Measurements of individual leaflets laying 90 degrees to each other demonstrate that this fern frond, and the rock it is in, was stretched by 350 percent during the collision of North America, Europe and Africa that formed Pangaea over 300 million years ago.
Other notable fact: Rhode Island lies on the east side of the Appalachian Mountains. Therefore, fossil plants from this site are more closely affiliated with plants from Europe and North Africa than from the rest of North America.

History

Let’s go back about 306 million years. What would become the North American continent was near the equator of the Earth. In what is now Rhode Island, the landscape once supported lush, tropical forests.