Mazon Creek Fish Coprolite
Coprolite (undetermined vertebrate producer) • Trace fossil, specifically a vertebrate coprolite containing prey remains (fish scales/debris)
Geological Period
Carboniferous (Pennsylvanian epoch)
Estimated Age
309 to 307 million years old
Preservation Type
Sideritic permineralization and authigenic mineral replacement within a nodule
Condition Assessment
Good condition, well-preserved nodule split displaying internal trace contents with minor surface weathering
Taxonomic Classification
Ichnofamily: Coprolitidae; Producer: Veretebrate (likely an ancient fish, shark, or amphibian)
Morphological Description
Ovoid to elongate shape with distinct concentric or spiral constriction lines. The surface reveals an organic-rich texture with visible micro-debris, including fragments of fish scales and bone material embedded within the ironstone concretion matrix.
Rock Matrix
Ironstone concretion (siderite-rich mudstone/shale nodule)
Formation & Location
Francis Creek Shale Member, Carbondale Formation, Mazon Creek region, Illinois, USA
Size & Dimensions
Approximately 4 to 6 cm in length, typical of medium-sized Carboniferous coprolites
Value & Rarity
Estimated Market Value
$20 to $50
Auction Estimate
$15 to $40
Rarity Assessment
Uncommon as a well-defined coprolite with visible inclusion content from the Mazon Creek Lagerstätte
Scientific Significance
Provides direct evidence of Carboniferous food webs, predator-prey dynamics, and dietary habits of Paleozoic aquatic predators
Preparation Recommendations
No aggressive preparation needed; gentle brushing to remove residual clay. Store in a stable, dry environment to prevent ironstone oxidation.
Notable Features
Distinct ovoid form enclosed in a classic Mazon Creek-style siderite nodule with visible internal scale impressions