Incomplete Brachiopod or Bivalve Shell Fragment
cf. Leiopteria sp. or Mucrospirifer fragment • Body fossil; Invertebrate (Macro-invertebrate)
Geological Period
Devonian (likely Middle Devonian)
Estimated Age
385 to 400 million years
Preservation Type
Recrystallized shell material; original calcium carbonate replaced by stable calcite or silica.
Condition Assessment
Fair; the specimen is incomplete with significant breakage and a puncture, though growth lines are visible.
Taxonomic Classification
Phylum: Brachiopoda or Mollusca; Class: Articulata or Bivalvia; Order: Likely Spiriferida or Pterioida
Morphological Description
A sub-triangular shell fragment displaying concentric growth lines and a prominent, elongated posterior wing or auricle. The surface shows a light pearlescent or calcitic luster with some breakage toward the dorsal margin and a significant hole in the mid-shell region.
Rock Matrix
None (isolated find); likely weathered out of Devonian limestone or calcareous shale typical of the Dundee Limestone or Traverse Group.
Formation & Location
Dundee Limestone or Traverse Group; Sterling State Park, Monroe, Michigan, USA.
Size & Dimensions
Approximately 15-25mm; typical for small to medium Paleozoic brachiopods or bivalve shells.
Value & Rarity
Estimated Market Value
$1.00 - $5.00
Auction Estimate
$0.00 - $10.00 (generally sold in bulk lots)
Rarity Assessment
Common; fragments of this type are frequently found along the Lake Erie shoreline and in Michigan glacial drift.
Scientific Significance
Provides evidence of Paleozoic marine fauna in the Michigan Basin. These fossils represent a time when Michigan was covered by a warm, shallow tropical sea.
Preparation Recommendations
Minor cleaning with water and a soft brush; store in a dry, padded container to prevent further chipping of the brittle edges.
Notable Features
Features a distinct 'wing' shape common in certain Devonian bivalves and brachiopods; the hole may be the result of modern mechanical weathering or ancient bioerosion.
Notes
Found at Sterling State Park Michigan