Stigmaria (Lycopodiophyte root trace)
Stigmaria ficoides (cf.) • Trace fossil (root cast/impression) of a Lycopodiophyte plant system
Geological Period
Carboniferous Period (specifically Mississippian to Pennsylvanian)
Estimated Age
298.9 to 358.9 million years
Preservation Type
Authigenic cast/impression preservation, likely involving siderite or iron-oxide replacement (permineralization of the surrounding cavity).
Condition Assessment
Fair to Good. While the diagnostic rootlet scars are clearly visible, the specimen is a small fragment, and the edges are broken and weathered.
Taxonomic Classification
Kingdom: Plantae, Phylum: Lycopodiophyta, Class: Isoetopsida, Order: Lepidodendrales, Genus: Stigmaria
Morphological Description
The specimen displays a characteristic pattern of circular indentations or pits (scars) arranged in a spiral or quincuncial pattern. These scars represent the attachment points for lateral rootlets known as 'appendices'. The surface between the pits appears smooth to slightly weathered, which is diagnostic of the outer cortex of these giant club-moss roots.
Rock Matrix
Reddish-brown ironstone/siltstone or ferruginous mudstone typical of coal-bearing strata; likely contains goethite or hematite giving it the rusty hue.
Formation & Location
Commonly found in the Carboniferous Coal Measures of North America (e.g., Pottsville Formation, Appalachian Basin) or Europe (e.g., South Wales or Northern England Coal Measures).
Size & Dimensions
The visible fossilized section measures approximately 4-6 centimeters across; this is a partial fragment of a plant system that could grow several meters in length.
Value & Rarity
Estimated Market Value
$15.00 - $35.00 USD
Auction Estimate
$20.00 - $50.00 USD (typically sold in bulk lots or as introductory specimens)
Rarity Assessment
Common. Stigmaria is one of the most widely distributed and easily found plant fossils in Carboniferous coal-bearing outcrops globally.
Scientific Significance
Provides evidence of Carboniferous swamp forest ecology. Stigmaria allows researchers to understand the subterranean anchoring systems of giant arborescent lycopsids like Lepidodendron and Sigillaria, which were key peat-formers and carbon sinks during the 'Coal Age'.
Preparation Recommendations
No chemical preparation required. Keep dry to prevent oxidation of iron minerals. Use a soft brush for cleaning; avoid water as it may destabilize the soft mudstone/siltstone matrix. Display in a relative humidity-controlled environment.
Notable Features
The distinctive circular pattern of scars is very well-defined against the iron-rich reddish matrix. Unlike leafy Lepidodendron bark which has diamond-shaped scars, the circular scars confirm this as the subterranean 'root' portion of the tree.