VERY RARE 10.5" Asineops squamifrons w/ 4" Diplomystus dentatus | 100% Natural | Green River Formation | Wyoming

Order Unknown, Family Asineopidae

Asineops (Greek for "donkey-faced") is the only member of the family Asineopidae and contains a single species, A. squamifrons. Asineops is known as the "mystery fish" as it lacks identifiable features that can clearly tie it to another known family of spiny-rayed fishes (Acanthomorpha). It appears to be a primitive acanthomorph fish.

Its numerous short dorsal spines, rounded tail margin, and enormous mouth distinguish it from other spiny-rayed fishes of the Green River Formation. While Asineops has been found in all three lakes of the Green River Formation, it is most prevalent in the Laney Member deposits of Lake Gosiute. It is very rare to find Asineops in the 18-inch layer and sandwich bed deposits of Fossil Lake, where specimens are usually much larger than those found in Lake Gosiute.

Diplomystus is an extinct genus of freshwater clupeomorph fish distantly related to modern-day extant herrings, alewives, and sardines. The genus was first named and described by Edward Drinker Cope in 1877.

Ray-finned Fish - Diplomystus dentatus

Order Ellimmichthyiformes, Family Paraclupeidae

The last known species of the Ellimmichthyiformes order went extinct sometime in the middle Eocene. D. dentatus is a primitive relative of the modern day herring. The genus Diplomystus is also known from fossil deposits in China.

D. dentatus is the 2nd most common fossil fish found from Fossil Lake. Specimens ranging from embryonic size (about 0.7 inches) to full-grown adults (about 26 inches) are common. Smaller-sized specimens are more commonly found in mid-lake than near-shore deposits. This suggests that D. dentatus spawned in open water.

This species' upturned mouth indicates it fed at the surface of Fossil Lake. D. dentatus specimens are commonly found with other fish stuck in their mouths, including other D. dentatus specimens.