Fossil Fish (Knightia or similar prehistoric bony fish in nodule)
cf. Knightia alta or Knightia eocaena • Body fossil, compression/impression preserved in a split nodule
Geological Period
Eocene (or potentially Cretaceous depending on precise nodule source, commonly Green River Formation or Santana Formation equivalents, but visually suggestive of a freshwater fish in ironstone/clay nodule)
Estimated Age
Approx. 40 to 50 million years old (Eocene epoch)
Preservation Type
Carbonaceous compression and mineral impression within a concretionary nodule, showing moderate relief upon splitting
Condition Assessment
Good. Complete split-nodule pair (part and counterpart) showing the full fish outline and internal skeletal structures, though some surface detail is weathered or obscured by iron oxide staining.
Taxonomic Classification
Phylum: Chordata, Class: Actinopterygii, Order: Perciformes, Family: Clupeidae (or similar primitive teleost), Genus: cf. Knightia
Morphological Description
Displays counterpart and part (positive and negative impressions) of a small teleost fish. The vertebral column runs centrally down the elongated, fusiform body. Fin rays are clearly visible near the dorsal and pectoral regions, and opercular bones are outlined near the head. Scale impressions and segmented vertebrae are moderately well-defined.
Rock Matrix
Fine-grained ferruginous siltstone or clay-ironstone nodule with reddish-brown oxidation halos
Formation & Location
Green River Formation (Wyoming, USA) or similar lacustrine deposit formations globally
Size & Dimensions
Approximately 8 to 10 cm in length, matching standard adult sizes for small fossil clupeid fishes
Value & Rarity
Estimated Market Value
$50 - $150 USD
Auction Estimate
$40 - $120 USD
Rarity Assessment
Common
Scientific Significance
Provides insight into Eocene lacustrine ecosystems, schooling behavior, and rapid fossilization processes within ancient lake deposits
Preparation Recommendations
Mechanical cleaning under a microscope using a fine pin-vise or air scribe to expose hidden bone details. Store in a stable, low-humidity environment to prevent further iron oxidation.
Notable Features
Preserved as a classic matched pair (part and counterpart) inside an oval-shaped nodule, highlighting the complete vertebral column and delicate fin ray impressions.