Devil's Toenail
Gryphaea arcuata (cf.) • Body fossil of an invertebrate marine bivalve (mollusk)
Geological Period
Jurassic (Early Jurassic specifically)
Estimated Age
199 to 175 million years ago
Preservation Type
Recrystallization of the original calcium carbonate (calcite/aragonite) shell structure
Condition Assessment
Good; shows a well-preserved curved left valve with clear growth ridges, though it lacks the smaller operculum (right valve) and shows slight weathering at the edges.
Taxonomic Classification
Kingdom: Animalia, Phylum: Mollusca, Class: Bivalvia, Order: Ostreida, Family: Gryphaeidae, Genus: Gryphaea
Morphological Description
Characterized by a thick, heavy, strongly curved left valve (the 'toenail' shape) with prominent growth lines and a much smaller, cap-like right valve that is often missing. The shell is calcareous and shows a distinct coiled or incurved umbo.
Rock Matrix
Likely originated from a grey liassic limestone or shale matrix, though the specimen appears cleaned of its surrounding substrate.
Formation & Location
Commonly found in the Blue Lias Formation of the United Kingdom and across coastal Europe, as well as various Jurassic marine deposits worldwide.
Size & Dimensions
Approximately 4-6 cm in height; this falls within the typical adult size range for this genus.
Value & Rarity
Estimated Market Value
$5.00 - $15.00 USD
Auction Estimate
$10.00 - $25.00 USD (typically sold in bulk lots for higher value)
Rarity Assessment
Common; these fossils are found in massive quantities in certain geological layers and are staple specimens for beginning collectors.
Scientific Significance
Gryphaea is a classic example of iterative evolution and provides significant data for studying ancient seafloor paleoecology, indicating high-energy marine environments where they lived unattached to the substrate.
Preparation Recommendations
Requires minimal preparation; can be cleaned with a soft brush and water. Should be stored in a dry environment to prevent any potential pyrite decay if metallic inclusions are present.
Notable Features
The specimen displays the classic 'coiled' morphology that led to the folklore name 'Devil's Toenail,' with well-defined concentric growth bands indicating the animal's seasonal growth cycles.