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Plant Fossil Identification - Carboniferous of Western PA - Conemaugh Group

Fossil Plant Material in Road Cuts near Pittsburgh and Ambridge, Pennsylvania
Pennsylvanian Coal Forest

~ 299 - 300 Million Years Old
Upper Pennsylvanian, Westphalian D to Stephanian A
Conemaugh Group: Glenshaw Formation: Mahoning Shale

Back to the Main Ambridge Fossils Page

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Carboniferous Plant Identification - Western PA sites

The Ambridge site and many nearby sites expose the remains of a Carboniferous Coal Forest. These remains are now fossilized in layers of shale from the Glenshaw Formation.

By far the most common plants are frond sections of the Pecopteris seed ferns, branch and trunk sections of the Calamites horse tails, and the needle like leaves from giant Lycopod scale trees. Other, less common plants include various Neuropteris seed ferns and a small plant called Sphenophyllum. One notable plant that is not found here, or very rare, is the Alethopteris seed ferns. They are very common to abundant in other formations, but not present here.

Below you can find a sample of fossils found at this location. Click on a thumbnail to go to the section about that plant. Each section includes reconstructions, descriptions, and fossil examples.

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Calamites: Horse Tail

Description

Calamites was a common Carboniferous tree-like plant that populated the swampy coal forests of the Carboniferous Period. The trunks of Calamites were thick, hollow, and segmented, sort of like bamboo today. They also had ribbed surfaces. A whorl of leaves, called Annularia radiated from each segment of the plant. Calamites could grow quite tall, possibly around 50 feet in height. Extinct Calamites are closely related to the small modern horsetail plants, Equisetum. An illustration of a reconstructed Calamites plant by Dunbar, 1963, can be seen to the right.

As fossils, Calamites are found as carbon films and as casts when sediments filled in the hollow stems.

Similar Fossils

Calamites trunk and branch sections are easy to identify due to thier segmented nature and the ribbed nature of the wood.

The leaves, called Annularia, are also easy to identify, as each leaf cluster is arranged in a distinct starburst pattern, with 8 or more leaves. However, the leaves of a shrub or vine like plant, Sphenophyllum, has similar looking leaves. In general, Sphenophyllum leaves are wider and more triangular. Also, sphenophyllum leaf clusters usually have less than 8 leaves.

Sample Fossils from Ambridge Shown Below: Calamates and Annularia
Calamites - Stem and Trunk Fragments

Calamites Leaves (Annularia):

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Cordaites: Early Conifer

Description

Cordaites is an extinct gymnosperm tree that grew in the swampy coal forests of the Carboniferous. These trees grew up to 100 feet in height and may have had root systems similar to that of mangrove trees. The leaves of Cordaites are strap like, meaning they are very long and narrow, growing up to lengths of 27 inches. The leaves are also very thick and leathery. A close inspection shows parallel leaf veins, making numerous parallel lines running down the leaf.

The term Cordaites technically only refers to the name of the leaves of this tree. The bark is called Mesoxylon, and the roots are called Amyelon.

Similar Fossils

Cordaites leaves are often found as fragmented carbon films. These can sometimes be confused with the long leaves of Lepidophylliodes. However, Lepidophylliodes do not have the numerous parallel veins running down the leaf.

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Sample Fossils from Ambridge Shown Below: Cordaites leaf fragments

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Lepidodendron: Scale Tree
Lycopod

Description

Lepidodendron is a common tree like plant that grew in the Carboniferous forests. This tree could exceed a height of 120 feet. It's closely related to club mosses of today. Lepidodendron is often called a "scale tree" due to the scale like imprints found on its trunk and limbs. These scale imprints are actually leaf scars from were leaves would exit the trunk and branches. The tree looked nothing like real trees , but instead had long, needle like leaves covering the entire trunk. This would give the entire tree a hairy looking appearance, as shown in accompanying the diagrams. The roots of scale trees are called "Stigmaria" fossils.

Similar Fossils

Lepidodendron branches and trunks look similar to other club moss type trees, such as Sigillaria. The difference is in the texture of the trunk sections. Lepidodendron has diamond shaped leaf scars, while Sigillaria has rows of parallel leaf scars.

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Sample Fossils from Ambridge Shown Below: Lepidodendron Scale Trees - Trunk and Limb Sections

Lepidodendron Scale Trees
Leaves

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Tree Ferns / Seed Ferns:
Neuropteris - Macroneuropteris - Pecopteris - Sphenopteris

Description

Seed Ferns, which are technically called (Peridospermatophyta), are some of the most common plants in the Carboniferous coal forests. They are often preserved as intricate carbon films and are prized by fossil plant collectors. The name comes from the fact that they had fern like foliage, but reproduced with seeds. Many seed ferns of the Carboniferous were tree like, while others were vine like. The tree forms did not have true trunks, but instead had a large trunk that was made from hundreds of tiny roots.

Two common seed ferns from the Pittsburgh area are Psaronius (Pecopteris) and Medullosa (Macroneuropteris).

Psaronius (Pecopteris)
Psaronius was a tree fern that grew up to 30 feet in height. The fern like fronds of Psaronius are composed of many small leaflets. The leaf fossils are called Pecopteris. Fossilized leaf sections are very common in the shale layers around Pittsburgh.

Medullosa (Macroneuropteris)
Medullosa was another tree fern that grew around 25 to 30 feet in height. The leaf fossils are called Macroneuropteris. Macroneuropteris is often called Neuropteris, which is a closely related tree fern. These fern trees often had larger leaves making up the fronds. Many different types of Macroneuropteris and Neuropteris fossils can be found throughout the Pittsburgh region.

Similar Fossils

Many Tree Ferns and other Seed Ferns look very similar to each other, and there are MANY types of fossil ferns. This often makes identification, even to the genera level, very difficult.

A good identification book is recommended.

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Sample of Tree Fern Fossils from Ambridge Shown Below:

Macroneuropteris scheuchzeri:

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Neuropteris ovata:

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Pecopteris sp. (Psaronius)

Pecopteris are by far the most common fossils found at the Ambridge site, and fossil fern sites around the Pittsbugh area.

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Sphenopteris:

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Sphenophylum: Shrub / Vining Plant:

Description

Sphenophyllum is a small plant from the Carboniferous coal forests. It's not a tree, but designated as a sprawling or scrambling plant, this is kind of like how a tomato plant would naturally grow if it was not staked up. They are usually less than 3 feet tall with many stems that would vine out. The stems contain whorls of leaf clusters. The individual leaves are fan shaped. There are less than 8 leaves per cluster. The leaf clusters are each around an inch or so in size.

Similar Fossils

Sphenophyllum fossils are easily confused with the leaves of calamites trees. The calamites leaves are called Annularia. Annularia leaves come in clusters of more than 8 leaves. The individual leaves are also much narrower than Sphenophyllum.

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Sample Fossils from Ambridge Shown Below: Sphenophyllum Leaf Clusters

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References / Works Cited

Dunbar, Carl O. (1963) Historical Geology. John Wiley & Sons, Inc.

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Recommended Books for Fossil Plants: