Brachiopod (Lamp Shell)
Rhynchonellid brachiopod (cf. Rhynchotrema or aff. Rhynchopora) • Body fossil; Invertebrate (Brachiopoda)
Geological Period
Likely Carboniferous or Devonian, though the group spans from Cambrian to present.
Estimated Age
Approx. 300 to 400 million years old
Preservation Type
Replacement/Recrystallization; the original aragonite or calcite shell material has likely been replaced by stable secondary calcite or silica, preserving the external ribs.
Condition Assessment
Good; the specimen appears largely complete (articulated valves), though the hinge area shows some surface erosion and matrix adhesion.
Taxonomic Classification
Phylum: Brachiopoda; Class: Rhynchonellata; Order: Rhynchonellida; Family: Rhynchonellidae
Morphological Description
Small, biconvex globose shell featuring distinct radial costae (ribbing) that fan out from the umbo/hinge area. It shows a strongly plicated (zigzag) anterior commissure typical of the Order Rhynchonellida.
Rock Matrix
Fine-grained sedimentary matrix, likely a weathered limestone or calcareous siltstone with some iron-staining (limonitic) on the exterior shell surface.
Formation & Location
Commonly found in marine formations such as the Burlington Limestone (USA) or the Carboniferous Limestone Supergroup (UK/Europe).
Size & Dimensions
Approximately 1.5 cm to 2.0 cm in diameter; this is a standard adult size for many small rhynchonellid species.
Value & Rarity
Estimated Market Value
$5 - $15 USD
Auction Estimate
$10 - $30 USD (usually sold in lots rather than individually)
Rarity Assessment
Common; Brachiopods are among the most abundant marine fossils in Paleozoic strata worldwide.
Scientific Significance
Brachiopods are vital index fossils used for biostratigraphic dating and provide deep insights into Paleozoic marine benthic ecosystems and water temperature gradients.
Preparation Recommendations
Mechanical cleaning with a soft brush and water; avoid acidic cleaners which could dissolve the calcareous shell. Store in a dry, stable environment.
Notable Features
Distinctive 'nut-like' shape with sharp, clear ribbing. The articulation remains intact, suggesting it was buried quickly after death in a low-energy environment.