Devonian Brachiopod (External Mold/Shell Fragment)
cf. Mucrospirifer mucronatus • Body fossil, invertebrate
Geological Period
Middle Devonian
Estimated Age
385 to 395 million years
Preservation Type
Recrystallized shell material or calcitic replacement; surface shows significant water-wear and erosion from beach activity.
Condition Assessment
Fair; the specimen is weathered and water-tumbled, causing the loss of fine costae (ribbing) and sharp hinge details, though the overall form remains identifiable.
Taxonomic Classification
Phylum: Brachiopoda; Class: Rhynchonellata; Order: Spiriferida; Family: Delthyrididae
Morphological Description
A single valve (likely a pedicle valve) showing a semi-elliptical to triangular outline with strong concentric growth lines. The specimen displays a slight alate (wing-like) extension typical of long-hinged spiriferids, though heavily worn.
Rock Matrix
Specimen is isolated from matrix, but likely originated from grey calcareous shale or limestone characteristic of distal Michigan Basin deposits.
Formation & Location
Traverse Group (specifically Dundee Limestone or Silica Shale equivalents), commonly found along the western shores of Lake Erie and SE Michigan.
Size & Dimensions
Approximately 25-35mm in width; consistent with adult growth stages of common Michigan Devonian brachiopods.
Value & Rarity
Estimated Market Value
$1.00 - $5.00 USD
Auction Estimate
$5.00 - $10.00 USD (as part of a multi-specimen lot)
Rarity Assessment
Common; these are among the most frequently found fossils in the Great Lakes region due to the massive volume of Devonian strata.
Scientific Significance
Provides evidence of the shallow, warm subtropical seas that covered the Michigan Basin during the Devonian. These organisms were crucial filter-feeders in Paleozoic reef ecosystems.
Preparation Recommendations
No further preparation required. Should be stored in a dry environment; can be cleaned with a soft brush and water if needed to remove beach salt/sand.
Notable Features
The smooth, bleached appearance is a result of natural tumble-polishing from the wave action of Lake Erie, making it a classic 'beach find' specimen.
Notes
Found at Sterling state park in Michigan