Green River Formation : Plants & Algae

More than any other group of fossils, plants are important in reconstructing the past climate of a fossil locality. For the Green River sites, the large number of temperate and sub-tropical taxa suggest that the region received ample rainfall, perhaps seasonally, and that temperatures were relatively mild.

Although most of the plant fossils are leaves, there are also fruits and seeds known.


Chondrides (?) - an alga

This specimen lay identified only as "algae" in our collections, despite the fact that it is unusually large and well-preserved for a fossil alga.

Sphenopsida (horsetails)

Equisetum winchesteri - a horsetail.

Horsetails are among the most recognizeable plant fossils. They are known from as early as the Carboniferous and there are still many species alive today. Stems of these plants usually are rough to the touch because of tiny silica crystals in the tissues.

Pteridopsida (ferns)

Lygodium kaulfussi - a climbing fern.

Species of Lygodium exist today in temperate Asia and eastern North America. They are often vine-like.

Asplenium delicatula - .

Aspenium is a large genus of fern, with many species surviving in eastern North America.

Acrostichum hesperium - .

Coniferopsida (conifers)

Pinus balli - a pine cone.

Sequoia cf. affinis - a redwood.

Magnoliidae (magnoliids)

Lindera varifolia - a linden tree.

The specimen is a holotype.

"Lower" Hamamelidae

Platanus wyomingensis - a sycamore.

The broad and toothed leaves of the sycamore are a common site for paleobotanists working in the Tertiary. Sycamores grow along streamsides where seasonal flooding helps to eliminate competing plants.

Rosidae (rosids)

Ptelea cassoidea - .

Winged fruit.

Ailanthus lesquereuxi - .

Winged seed.