Green River Formation Fish Fossils

During the Eocene, based on the fossil record, the region was sub-tropical to temporate. Some 60 vertebrate taxa have been described from the formation, as well as abundant invertebrates and plants. Green river has been noted for its well-preserved fish since mid-way through the 19th century. The unusually excellent preservation of the Green River fish fossils is usually attributed to a combination of two factors: 1) a cold period during the Eocene that would have caused dead fish to sink faster due to a less inflated swim bladder; and 2) the great depth of the lakes and the consequent anoxic conditions that would have often prevented scavengers from disturbing the carcasses.

Fossil fish eating fish (or aspiration) from the Green River Formation.

The majority of fish fossils are taken from the Fossil Lake area are from two layers: 1) the so-called 18-inch layer; and 2) the spilt fish layer. The best preserved fish come from the 18-inch layer. Becuase the sediment is highly laminated, the fish can often be removed nearly whole. This layer, in the area near Fossil Butte, does indeed avarage about 18 inches in thickness, and represents some 4000 of deposition. The composition of the limestone indicates that the layer was formed in deep water far from shore. By contrast, the so-called split-fish layer is unlaminated making extraction and preparation of the best fossil fish far more difficult. The layer is about six feet thick, and the fauna indicates water that was better circulated than that associated with the 18-inch layer. Some 19 genera of Eocene fish come from the Green River formation.

 

Genus	Common Name	Fish Classication: Class Chondrichthyes Class Actinopterygii		Number of species	Relative abundance	Picture & Link
		Order	Family
Priscacara liops	Perch	Perciformes	Priscacaridae	2	Common
Priscacara serrata					Less common than liops
Heliobatis radians	skate or stingray	Rajiformes	Dasyatidae	1	Rare
Lepisosteus simplex	gar fish	Lepisosteiformes	Lepiosteidae	3	Rare
Lepisosteus cuneatus
Amia	bowfin	Amiiformes	Ammiidae	2	Extremely rare
Phareodus encaustus		Osteoglossiformes	Osteoglossidae	2	Uncommon
Phareodus testis		Osteoglossiformes	Osteoglossidae	2	Uncommon
Knightia	herring	Clupeiformes	Clupeidae	2	Extremely common
Diplomystus	herring	Ellimmichthyiformes	Ellimmichthyidae	1	Common
Notogoneus		Gonorynchiformes	Gonorynchidae	1	Uncommon
Mioplosus	perch	Perciformes	Percidae	2	Uncommon
Gosiutichthys	herring	Clupeiformes	Clupeidae	1	Rare
Eohiodon	mooneye	Osteoglossiformes	Hiodontidae	1	Extremely rare	.
Crossopholis	paddlefish	Acipenseriformes	Polydontidae	1	Extremely rare	.
Amyzon	sucker	Cypriniformes	Catostomidae	1	Rare	.
Astephus	catfish	Siluriformes	Ictaluridae	1	Very rare	.
Hypsidoris	catfish	Siluriformes	Ictaluridae	1	Extremely rare	.
Erismatopterus	trout	Percopsiformes	Percopsidae	1	Rare	.
Amphiplaga	trout	Percopsiformes	Percopsidae	1	Rare	.
Asineops		Incertaesedis	Asineopidae	1	Rare	.

References and image credits:
Grande, L, Paleontology of the Green River Formation, with a Review of the Fish Fauna, Ed2, The Geological Survey of Wyoming Bulletin 63 (1984)
Fossil Mall Fish Fossils.