Fagopsis longifolia: an Extinct Species from Florissant

Fagopsis longifolia is one of the more common fossil plants found in the Florissant Formation. Located 35 miles west of Colorado Springs, Florissant Fossil Beds National Monument has one of the most diverse fossil deposits in the world—more than 1,700 different species have been described from this ancient lake deposit. Fagopsis, a genus that became extinct at the end of the Eocene, is thought to have been a member of the beech family (Fagaceae). Originally identified as the water elm, Planera, these fossil leaves were assigned to the genus Fagopsis.

Fagopsis longifolia is one of the most abundant fossils found in the Florissant Formation. The length of the leaves are 5 to7 cm (1.9 to 2.75 inches); and the width is from 2.5 to 3 cm (1 to 1.2 inches). Specimen FLFO3129a, Florissant Fossil Beds National Monument. Image by Russell Wood.

Fagopsis is known from just 30 other fossil specimens from the North American Eocene. Although Fagopsis longifolia is among the most abundant fossils at Florissant, this species has not been found anywhere else in the world. Fagopsis thrived along the prehistoric Florissant streams and the edges of ancient Lake Florissant, dropping its abundant leaves onto the water. Towering redwoods (Sequoia) also grew around the borders of the lake and along streams.

This brochure, featuring one of the Sequoia stumps of the Florissant fossil beds, was used to attract visitors to the fossil beds when it was a tourist attraction. Huge, petrified Sequoia trees are the largest fossils found in the monument—some have the largest diameter petrified trees known. Brochure image courtesy of the Beth Simmons collection.

Fossil plants, just like Fagopsis longifolia, provide important information about paleoclimate and the uplift history (paleoelevation) of the Rocky Mountains in the prehistoric past. Fagopsis represents plants found in a moister climate than the cool, dry climate of Florissant today. Based on characteristics of Fagopsis and other fossil plants, scientists have estimated the mean annual temperature at Florissant during the Late Eocene at approximately 10.7° to 14°C (51.2° to 57.2° F) with an estimated paleoelevation of 1,899 to 3,299 meters (6,230 to 10,500 feet) Note: there is counterevidence from non-floral studies that propose different mean annual temperatures and paleoelevations. Researchers are still working on this problem] Florissant also represents a time period just before a major cooling of the world’s climate that occurred during the end of the Eocene and at the dawn of the Oligocene .

Fossils of Fagopsis longifolia are found between layers of paper-thin lake shales in the Florissant Formation from the latest part of the Eocene (34 million years ago).  Most of the Florissant fossils are detailed compression and impression fossils of insects and plants. Image by Donald Miranda.

The conditions of ancient Lake Florissant led to exceptional fossil preservation and preserved a number of fossils—like Fagopsis longifolia—that are used by researchers as proxies or useful indicators for reconstructing ancient environments and understanding biological evolution, paleoclimate, paleoelevation, and climate change.