Solitary Rugose Coral (Horn Coral)
Grewingkia canadensis • Body fossil; Invertebrate (Cnidaria)
Geological Period
Late Ordovician
Estimated Age
445 to 450 million years
Preservation Type
Recrystallization / Permineralization; the original aragonite/calcite skeleton has been replaced by more stable microcrystalline calcite or silica.
Condition Assessment
Fair; the specimen is complete in form but heavily water-worn (tumbled), which has smoothed the diagnostic external growth rugae and sharpened the profile.
Taxonomic Classification
Phylum: Cnidaria; Class: Anthozoa; Order: Stauriida; Suborder: Streptelasmatina; Family: Streptelasmatidae; Genus: Grewingkia
Morphological Description
Conical, horn-shaped calyx showing a water-worn, rounded surface. Features internally radiate septa (vertical plates) visible at the blunt end and fine longitudinal striations on the exterior theca. The specimen shows significant stream-rounding from river transport.
Rock Matrix
Bioclastic limestone/shale matrix (typical of the Cincinnati Arch area), though this specimen is mostly free of matrix due to river erosion.
Formation & Location
Whitewater Formation, Richmond Group; Brookville, Indiana, USA (Cincinnati Arch region).
Size & Dimensions
Approximately 4-6 cm in length; consistent with mid-to-large sized solitary corals of the Ordovician Period.
Value & Rarity
Estimated Market Value
$5 - $15 USD
Auction Estimate
$10 - $25 USD (for a small lot of similar specimens)
Rarity Assessment
Common; Brookville and the surrounding Whitewater River valley are world-renowned for the abundance of these specific corals.
Scientific Significance
A diagnostic 'index fossil' for the Late Ordovician Cincinnati Arch sediments; indicates a shallow, warm, epicontinental sea environment with moderate wave action.
Preparation Recommendations
No further mechanical preparation needed. Clean with water and a soft brush; store in a dry environment. A light coating of mineral oil can enhance the visibility of internal septa.
Notable Features
Distinctive 'horn' curvature and the visible internal septal arrangement revealed by the stream-worn blunt end. Its provenance in Brookville confirms it as part of the classic Cincinnatian lagerstätte fossils.
Notes
found in a river bed in brookville indiana in the whitewater river