Brachiopod (Lamp Shell)
Pseudoatrypa cf. devoniana • Body fossil, invertebrate
Geological Period
Devonian (likely Middle Devonian)
Estimated Age
360 to 419 million years
Preservation Type
Recrystallization (calcite replacement) with potential minor permineralization
Condition Assessment
Good; showing clear growth bands and morphological symmetry, though the ventral margin appears to have minor chipping.
Taxonomic Classification
Phylum: Brachiopoda, Class: Rhynchonellata, Order: Atrypida, Family: Atrypidae
Morphological Description
Sub-circular to biconvex shell with prominent growth lines and fine radial costae. Shows a characteristic low-profile umbo and a slightly curved anterior margin.
Rock Matrix
Specimen is shown free of matrix, but typically originates from calcareous shale or limestone characteristic of the Traverse Group.
Formation & Location
Traverse Group or Dundee Limestone, Sterling State Park (Monroe County), Michigan, USA
Size & Dimensions
Approximately 20-30mm in width, which is typical for adult specimens of this genus.
Value & Rarity
Estimated Market Value
$5.00 - $15.00 USD
Auction Estimate
$10.00 - $25.00 USD (typically sold in lots)
Rarity Assessment
Common; Brachiopods are among the most abundant fossils in the Paleozoic strata of the Great Lakes region.
Scientific Significance
Provides data on Devonian marine biodiversity in the Michigan Basin, an area once covered by a shallow subtropical sea.
Preparation Recommendations
Gentle cleaning with a soft brush and water; no harsh chemicals needed as the calcite is stable. Store in a dry, padded container.
Notable Features
Excellent preservation of concentric growth lines which represent seasonal or episodic growth cycles of the organism.
Notes
Found at Sterling State Park in Michigan