9.9" Fossil Fish (Mioplosus) - Uncommon Species - 18 Inch Layer

Mioplosus is a genus of large extinct perciform fish that lived through the Eocene epoch. This genus is easily distinguished by an elongate fusiform body, double dorsal fins, and forked tail. Mioplosus was a solitary predator with large teeth: a few fossil specimens have been collected with other, smaller fish lodged in their throats. Most fossils of this genus are from the Tertiary-aged Green River Formation in Wyoming, though relatives of this genus are known to range throughout Asia and New Zealand. Mioplosus is also believed to be related to the modern pike-perch of the genus Sander (Stizostedion).

About The 18 Inch Layer Of Fossil Lake

Specimens of this quality come from the coveted 18-inch layer of the Green River Formation, a horizon renowned for producing exceptionally dark, detailed, and well-preserved fossil fish. The limestone from this layer is significantly harder and more durable than that found in many other parts of the formation, likely a result of the deep-water conditions under which it was originally deposited.

These conditions helped preserve fish in remarkable completeness, allowing exceptional specimens to be recovered largely intact. Locating them is a specialized process. The layer is often worked at night using low-angle lighting, which reveals the subtle raised contours created by a fossil fish—particularly the backbone—hidden beneath the surface of the limestone.



Once identified, the surrounding rock is carefully cut away and the specimen is transported to a preparation laboratory. Because the fossil may lie as much as an inch beneath the surface, exposing it requires painstaking work under magnification. Skilled preparators use fine hand tools to gradually remove the overlying limestone, revealing the fossil in extraordinary detail while preserving the delicate bones beneath.