Rudist Bivalve Internal Mold (Steinkern)
cf. Toucasia sp. • Body fossil (internal mold or steinkern), Invertebrate
Geological Period
Cretaceous
Estimated Age
100 to 66 million years ago
Preservation Type
Natural internal mold (steinkern) with complete replacement by microcrystalline calcite/limestone
Condition Assessment
Good condition; a solid, stable internal mold with natural weathering on the extremities and a characteristic perforation, completely intact structurally with no modern breaks
Taxonomic Classification
Phylum: Mollusca, Class: Bivalvia, Order: Hippuritida, Family: Requieniidae or Caprinidae, Genus: cf. Toucasia
Morphological Description
The specimen exhibits a distinctive curved, asymmetrical, horn-shaped or twisted profile with a central perforation or deep indentation characteristic of the attachment and growth cavities of unequal-valved rudist clams. The surface is weathered and smooth with fine granular texture typical of limestone steinkerns, showing no original shell material remaining.
Rock Matrix
Dense Cretaceous limestone and dolomite typical of the Texas Hill Country, with minor iron oxide staining on the exterior surfaces
Formation & Location
Fredericksburg Group / Glen Rose Formation, Kerr County, Texas, USA
Size & Dimensions
Approximately 10 to 12 cm in maximum length, comparable to medium-sized rudists of the Lower Cretaceous shallow marine carbonate platforms
Value & Rarity
Estimated Market Value
$20 to $50 USD
Auction Estimate
$15 to $40 USD
Rarity Assessment
Common throughout the Cretaceous limestone formations of Central Texas
Scientific Significance
Provides evidence of extensive Cretaceous shallow tropical marine environments (rudist reefs) that once covered large parts of Texas before closing of the ancient seaways
Preparation Recommendations
No aggressive preparation needed. Wash gently with warm water and a soft brush to remove residual surface dirt. Store in a dry environment at stable room temperature.
Notable Features
The prominent curved shape and natural through-hole (perforation) formed by sediment filling the complex internal cavity between the asymmetrical valves make it a visually striking geological specimen
Notes
Kerr county Texas