Spiriferid Brachiopod
Mucrospirifer cf. mucronatus • Body fossil, Marine Invertebrate
Geological Period
Devonian (possibly Silurian to Carboniferous)
Estimated Age
360 - 410 million years
Preservation Type
Recrystallized replacement (likely calcite or silica) within a sedimentary matrix.
Condition Assessment
Good. The specimen shows clear ribbing and a mostly intact hinge line, though some weathering is visible on the shell surface and edges.
Taxonomic Classification
Phylum: Brachiopoda, Class: Rhynchonellata, Order: Spiriferida, Family: Spiriferidae, Genus: Mucrospirifer (or similar)
Morphological Description
Characteristic 'wing-like' elongated hinge line with a biconvex shell. Features a distinct central fold and sulcus with strong radial costae (ribbing) extending from the beak to the anterior margin. The valve shows a roughly triangular or trapezoidal outline.
Rock Matrix
Fine-grained grey limestone or calcareous shale matrix, typical of Paleozoic marine deposits.
Formation & Location
Commonly found in the Hamilton Group of New York and Ontario, or the Silica Shale of Ohio, USA.
Size & Dimensions
Approximately 3-5 cm in width; typical for the Mucrospirifer genus which is known for its wide, winged appearance.
Value & Rarity
Estimated Market Value
$10 - $25 USD
Auction Estimate
$15 - $40 USD (usually sold in lots at auction)
Rarity Assessment
Common. These are among the most abundant and recognizable fossils in Paleozoic marine strata.
Scientific Significance
Spiriferids are important index fossils used for biostratigraphy. They provide insights into Devonian seabed ecosystems and the diversity of filter-feeding organisms before the Permian mass extinction.
Preparation Recommendations
Mechanical cleaning with a soft brush; avoid harsh acids which may dissolve the calcareous shell. Store in a dry, stable environment to prevent 'pyrite disease' if trace minerals are present.
Notable Features
The specimen exhibits the classic 'butterfly' shape that gave this group their common name; the symmetry between the left and right 'wings' is well-preserved.