Knightia eocaena (Freshwater Herring)
Knightia eocaena • Body fossil; Vertebrate (Actinopterygii)
Geological Period
Eocene Epoch (Paleogene Period)
Estimated Age
Approx. 48 to 52 million years
Preservation Type
Carbonization and replacement; the organic matter has been replaced by minerals leaving a dark carbon film that highlights skeletal details against the lighter matrix.
Condition Assessment
Very Good; the specimen shows high articulation of the skeleton and minimal scavenging disruption, though some distal fin rays are faint.
Taxonomic Classification
Phylum: Chordata, Class: Actinopterygii, Order: Ellimmichthyiformes, Family: Paraclupeidae, Genus: Knightia
Morphological Description
Compressiform body shape typical of schooling fish. Features a clearly defined vertebral column, well-preserved rib cage, and dorsal fin. The skull shows orbital structure and operculum. The tail is homoceral (forked). Characteristic row of abdominal scutes (specialized scales) along the ventral midline.
Rock Matrix
Fine-grained, laminated lime mudstone (oil shale) from a lacustrine (lake) environment.
Formation & Location
Green River Formation, specifically Fossil Lake members, Wyoming, USA.
Size & Dimensions
Approximately 12-15 cm in length; falls within the typical adult range for Knightia eocaena (usually 6-15 cm).
Value & Rarity
Estimated Market Value
$150 - $450 USD
Auction Estimate
$200 - $600 USD
Rarity Assessment
Common; while it is one of the most common vertebrate fossils in the world, high-quality articulated specimens with professional preparation are highly sought after.
Scientific Significance
Knightia is Wyoming State Fossil and provides vast data on Eocene lake ecosystems (Lakes Gosiute, Uinta, and Fossil). It serves as a key indicator species for mass mortality events caused by seasonal changes or algae blooms.
Preparation Recommendations
Mechanical preparation using air scribes or pin tools to remove the thin layer of matrix over the bone. Do not use acid. Seed with a thin layer of matte sealer to prevent flaking and store in a low-humidity environment.
Notable Features
Deep relief preparation style; the surrounding matrix has been recessed to emphasize the specimen's silhouette. Excellent preservation of the delicate caudal fin rays and neural spines.