Trilobite Pygidium (Tail Segment)
Eldredgeops rana cf. • Body fossil (Invertebrate arthropod exoskeleton fragment)
Geological Period
Devonian (likely Middle Devonian)
Estimated Age
385 to 400 million years
Preservation Type
Recrystallized replacement (calcitization) within a mineralized matrix.
Condition Assessment
Fair; the specimen is an isolated pygidium (disarticulated tail piece) rather than a complete enrolled or prone individual. Significant weathering is present on the right margin.
Taxonomic Classification
Phylum: Arthropoda, Class: Trilobita, Order: Phacopida, Family: Phacopidae, Genus: Eldredgeops (formerly Phacops)
Morphological Description
A semi-circular, convex pygidium (tail) showing a distinct central axis (rachis) with approximately 4-6 segments and lateral pleural ribs. The surface texture is finely granulated, a hallmark of the Phacopid order. The pleural furrows are visible, though partially eroded.
Rock Matrix
Gray calcareous shale or argillaceous limestone; typical of marine sedimentary deposits.
Formation & Location
Likely from the Hamilton Group (New York / Pennsylvania, USA) or the Silica Shale Formation (Ohio, USA).
Size & Dimensions
Approximately 12-15mm in width; this represents a medium-sized specimen relative to typical full-grown Eldredgeops specimens which reach 30-50mm in total body length.
Value & Rarity
Estimated Market Value
$5.00 - $15.00 USD
Auction Estimate
$10.00 - $25.00 USD (typically sold in bulk lots for this quality level)
Rarity Assessment
Common; Phacopid trilobite fragments are ubiquitous in Eastern North American Devonian deposits.
Scientific Significance
Provides evidence of local benthic marine paleoenvironments and facilitates biostratigraphic dating of the rock strata. Demonstrates typical Devonian arthropod morphology.
Preparation Recommendations
Mechanical cleaning via air-abrasive (dolomite powder) could improve contrast, but the small size and partial nature suggest keeping it in its current natural matrix condition. Store in a dry, UV-protected case.
Notable Features
Features the classic 'frog-spawn' texture of the Phacopid cuticle; well-defined axial rings are preserved despite the small size of the fragment.