Rudist Bivalve Internal Mold
Rudist bivalve indet. (cf. Requienia or similar reef-building rudist form) • Internal mold and cast, invertebrate body fossil
Geological Period
Cretaceous
Estimated Age
66 to 145 million years old
Preservation Type
Natural internal mold (steinkern) with partial replacement by calcite and limestone infill.
Condition Assessment
Fair to Good. The specimen is an incomplete fragment representing primarily the internal mold of the lower conical valve, showing moderate surface weathering and wear on the margins, but retaining clear diagnostic internal structural outlines.
Taxonomic Classification
Phylum: Mollusca, Class: Bivalvia, Order: Hippuritida, Family: Requieniidae or Rudistae
Morphological Description
The specimen exhibits a thick-shelled, asymmetrical conical structure typical of rudist bivalves. The internal mold shows characteristic coarse corrugations or growth rugae along the lateral edges, and a deeply recessed central cavity representing the internal body chamber. The preservation highlights the internal shape of the lower cone valve.
Rock Matrix
Light grey to buff-colored micritic limestone typical of shallow marine Tethyan Cretaceous deposits.
Formation & Location
Tethyan realm deposits, commonly found in Cretaceous limestone formations across Southern Europe, North Africa, and the Middle East, as well as the Glen Rose Formation of Texas.
Size & Dimensions
Approximately 4 cm to 5 cm in length, which is consistent with medium-sized individual rudist cones or fragments from larger reef-building colonies.
Value & Rarity
Estimated Market Value
15 to 45 USD
Auction Estimate
20 to 50 USD
Rarity Assessment
Common, as rudist fragments and internal molds occur abundantly in many Cretaceous limestone formations globally.
Scientific Significance
Rudists were major reef-builders during the Cretaceous period, acting as the primary framework organisms for carbonate platforms before going extinct at the Cretaceous-Paleogene boundary. This specimen provides insight into shallow tropical marine paleoenvironments and rudist paleobiology.
Preparation Recommendations
Mechanical cleaning with a fine brush to remove loose surface matrix. Store in a stable, dry environment. No complex conservation treatments are required.
Notable Features
Clear internal mold morphology showing the distinct asymmetrical growth axis and internal cavity of a reef-dwelling Cretaceous bivalve.