Brachiopod (Spiriferid)
cf. Mucrospirifer sp. (Butterfly Shell) • Body fossil; Invertebrate (Brachiopoda)
Geological Period
Devonian to Carboniferous (Mississippian)
Estimated Age
350 - 410 million years
Preservation Type
Replacement/Recrystallization; original calcium carbonate likely replaced by silica or calcite with high fidelity to surface texture.
Condition Assessment
Good to Very Good; valves are articulated and the symmetry is well-preserved, though some slight weathering is visible on the distal ends of the 'wings'.
Taxonomic Classification
Phylum Brachiopoda, Class Rhynchonellata, Order Spiriferida, Family Spiriferidae
Morphological Description
Displaying a classic 'winged' or mucronate outline with elongated hingelines. The shell possesses a prominent central fold and sulcus with coarse radiating costae (ribbing) that fan out from the umbo toward the margins. The valves are articulated and show a biconvex profile typical of spiriferids.
Rock Matrix
Small amount of grey calcareous shale or limestone residue visible within the rib grooves.
Formation & Location
Likely derived from the Hamilton Group (New York/Ontario) or the Silica Shale (Ohio/Michigan), USA/Canada.
Size & Dimensions
Approximately 3-5 cm in width; typical size for a mature Mucrospiriferid specimen.
Value & Rarity
Estimated Market Value
$5.00 - $15.00 USD
Auction Estimate
$10.00 - $25.00 USD (typically sold in lots)
Rarity Assessment
Common; spiriferid brachiopods are among the most abundant and widely distributed Paleozoic invertebrate fossils in North America.
Scientific Significance
Brachiopods are essential index fossils for the Paleozoic era and serve as indicators of ancient shallow marine environments and water clarity. They provide data on historical biodiversity and mass extinction recovery.
Preparation Recommendations
Keep dry; gentle cleaning with a soft brush or water and mild soap if needed to remove grime. No intensive stabilization required given the robust mineralization.
Notable Features
Features highly distinct 'wing-like' lateral extensions and a sharply defined fold-and-sulcus structure, characteristic of the 'Butterfly' shells often found in the Devonian of the Great Lakes region.