Plant FossilPlants can be divided into two main groups: those that reproduce by microscopic spores, and those that reproduce by seeds. Examples of spore-bearing plants are mosses, true ferns, horsetail rushes, and club mosses. Seed-bearing plants are most abundant in Kentucky today. Examples are grasses, tobacco, oaks, maples, and poison ivy. Fossils of both groups are abundant in parts of Kentucky. Plant fossils have been found in black shales of Devonian age in the Knobs Region, in shales and sandstones of the Eastern and Western Kentucky Coal Fields, and in clay, shale, and sands of the Cretaceous and Tertiary sediments of the Jackson Purchase Region.

Devonian Plants

The most commonly found plant fossils in the Devonian black shales of Kentucky are silicified logs (called Callixylon) of the seed-fern tree, Archaeopteris. Seed ferns are described later. Several silicified fossil logs from these shales in Kentucky are on display at the Smithsonian Institution in Washington, D.C. Rarely, foliage from these and other plants is found in these Devonian shales. Closer to Kentucky, a reconstruction of a Devonian forest, with silicified stumps from Kentucky, can be seen at Falls of the Ohio State Park on the Indiana-Kentucky line.

Devonian Plants fossil
Devonian Plants fossil
Devonian Plants fossil
Devonian Plants

Mississippian Plants

Late Mississippian shales and sandstones in some places contain plant fossils of scale trees (described later) and seed ferns (also described later) that were preserved in coastal deposits. These fossils are not generally common in Mississippian rocks, though, because most rocks of this age were deposited in shallow seas and not in coastal areas.

Pennsylvanian Plants

The most abundant plant fossils in Kentucky are found in Pennsylvanian rocks in the State's two coal fields. The Pennsylvanian, for the eastern United States, was a time of tropical, humid climate and lush forests. The large number of coals in the coalfields is a result of these conditions; coal is fossil peat, and peat is the accumulation of plant debris, and the abundance of plant debris results from the large lowland forests. For more discussion about coal, see our section on coal information.

The plants of the Pennsylvanian were not like those of today. The forests of the eastern United States today are dominated by seed-bearing woody trees, bushes and herbaceous plants. During the Pennsylvanina, the dominate plants were spore-bearing (they reproduced by spores, not seeds). Large trees existed, but they were not woody trees; they were composed of thick bark with a central, pithy core. There were seed-bearing plants during the Pennsylvanian, but they were not similar to the modern ones. There were no flowering plants at all. Let's take a look at the kinds of plants that were common then.

Spore-bearing plants

Scale trees (lycopods), related to the modern club mosses or ground pine in Kentucky, also grew to be trees over 100 feet tall. They are called scale trees because their bark looked like the scales of a snake. Modern lycopods seldom reach over 1 foot in height.

lepidostrobus, lepidodendron, stigmaria, lycopod

Stumps and roots of the scale trees, like the one above, are very common fossils in the coal fields; the roots go by the scientific name Stigmaria.

Fossil stumps are common in the roofs of some deep coal mines, where they are called kettlebottoms by miners. Kettle bottoms are a hazard to miners because they sometimes fall out of the roof of the mine after the coal has been removed.

Calamite plants were similar to modern horsetail rushes, but some grew as trees over 100 feet tall. The common calamite tree fossil is represented by the genus Calamites. Modern horsetail rushes don't generally get larger than 4 or 5 feet tall.

calamite plants fossil

In the coal fields, common fossils of spore-bearing plants are true ferns (filicopsids), calamites (large horsetail rushes), and scale trees (lycopods). True ferns (as opposed to seed ferns) are similar to the ferns living today; they produce spores somewhere on the plant, which are used to reproduce new plants. Some of the true ferns were large and are called tree ferns. Some tree ferns live in the tropics today. Most of the fern-like fossils found in Kentucky's coal fields are seed ferns (pteridosperms), described in another section.

Seed-bearing plants

The gymnosperms are the only seed-bearing plants of the Pennsylvanian forests, there were no flowering plants in existance. The two common types of gymnosperm fossils found in Kentucky are the pteridosperms (seed ferns) and the cordaites (strap-leafed trees). Early conifers likely existed in Kentucky as well.

alethopteris
seed neuropteris

The seed ferns grew to small tree size and had leaves similar to the true ferns. The big difference between seed ferns and true ferns is that the seed ferns had seeds, which are sometimes fossilized, and the true ferns had only microscopic spores. The group of plants called seed ferns is extinct, but most of the modern seed-bearing plants descend from them. The leaves (fronds) and seeds of seed ferns are common fossils in the Eastern and Western Kentucky Coal Field and are more common than true-fern fossils.

Cordaite trees (represented by the genus Cordaites) had long strap-like leaves and winged seeds. Fossils of the cordaite limbs, leaves, and seeds are common in some areas of the coal fields. The cordaite plant group is extinct.

Standing upright fossil trees Learn more

Cretaceous

Late Cretaceous sands and clays in the Jackson Purchase Region (extreme western Kentucky) sometimes contain coalified limbs and logs of trees. No studies are currently known that identify the types of trees that these fossils represent, but their thick woody structure suggests that they are either conifer (gymnosperms) or flowering-plant (angiosperms) trees.

Tertiary

The Tertiary sands and clays of the Jackson Purchase Region contain fossil stumps, limbs, and logs of woody trees (probably conifer or flowering-plant types), and rarely leaves of flowering-plant trees (angiosperms).

 

 

 

Last Modified on 2020-06-01
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