Fossil Oyster
Gryphaea cf. dilatata or Exogyra sp. • Body fossil, invertebrate marine bivalve
Geological Period
Jurassic (Callovian to Oxfordian) / Cretaceous
Estimated Age
165 to 150 million years old
Preservation Type
Original calcitic shell material preserved with minor surface weathering and sediment infilling
Condition Assessment
Good, showing clear structural integrity of the lower valve with minor wear along the margins
Taxonomic Classification
Phylum Mollusca, Class Bivalvia, Order Ostreida, Family Gryphaeidae or Ostreidae, Genus Gryphaea or Exogyra
Morphological Description
Asymmetrical bivalve shell showing a deeply cupped left valve with a strongly curved umbo and concentric growth lines along the exterior surface, typical of oysters adapted to soft substrates.
Rock Matrix
Argillaceous marl / marly limestone typical of coastal cliff formations
Formation & Location
Callovian and Oxfordian formations of the Vaches Noires cliffs (Falaises des Vaches Noires), Normandy, France
Size & Dimensions
Approximately 4 to 5 cm in length, consistent with medium-sized specimens of the taxon
Value & Rarity
Estimated Market Value
10 to 25 USD
Auction Estimate
5 to 15 USD
Rarity Assessment
Common, frequently found weathering out of the clay and marl layers at the given locality
Scientific Significance
Provides evidence of shallow marine shelf paleoenvironments and benthic community structures during the Jurassic period in Western Europe
Preparation Recommendations
Gentle mechanical cleaning with a soft brush and water to remove remaining clay matrix; no special consolidants needed
Notable Features
Well-defined attachment scar area and clear concentric growth lamellae demonstrating asymmetric cementation habits
Notes
falaises des Vaches Noires