Fossilized Clam or Bivalve Fragment
Indeterminate bivalve species; identification is limited by partial preservation • Body fossil (Invertebrate Bivalve Mollusk)
Geological Period
Devonian (likely Middle to Late Devonian)
Estimated Age
360 to 400 million years
Preservation Type
Permineralization and replacement; possible recrystallization of the shell material giving it a marble-like sheen.
Condition Assessment
Fair; the specimen is incomplete (fragmentary) and shows significant water-worn erosion from being found in a beach/state park setting.
Taxonomic Classification
Phylum: Mollusca, Class: Bivalvia, Order: Pteriida (likely), Family: Unknown, Genus: cf. Paracyclas or similar Devonian genera
Morphological Description
The specimen shows a partial valve with prominent concentric growth lines and a distinct, pointed umbo (the beak). The shell material appears thickened at the hinge area with a smooth, slightly pearlescent surface suggesting original aragonite or calcite replacement.
Rock Matrix
None attached; the specimen appears as a loose surface-collected clast, likely weathered out of limestone or shale common in the Michigan Basin.
Formation & Location
Likely from the Dundee Limestone or Traverse Group; commonly found along the coastal regions of the Michigan Basin and Lake Erie shoreline.
Size & Dimensions
Approximately 2.5 to 4 cm in length; typical for medium-sized Devonian brachiopods or small bivalves.
Value & Rarity
Estimated Market Value
$5.00 - $15.00 USD
Auction Estimate
$10.00 - $20.00 USD
Rarity Assessment
Common; bivalve fragments of this era are ubiquitous in the fossiliferous strata of the Great Lakes region.
Scientific Significance
Provides evidence of the shallow, warm epicontinental seas that covered Michigan during the Devonian. Illustrates the diversity of seafloor-dwelling mollusks in the Michigan Basin.
Preparation Recommendations
No invasive preparation needed; clean with water and a soft brush. Store in a dry environment to prevent further mechanical erosion.
Notable Features
The specimen exhibits high-contrast concentric banding and a very well-preserved pointed morphology at the beak, which is often lost to erosion.
Notes
Found at Sterling State Park Michigan