Green River Formation Fish Fossils

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Fish Fossils of the Green River Formation


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The Green River Formation
Fossils of the Green River Formation

 

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
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 simplex fossil gar fish
bowfin
Amiiformes
Ammiidae
2
Extremely rare
Amia fossil fish
 
Osteoglossiformes
Osteoglossidae
2
Uncommon
Phareodous fossil fish
Osteoglossiformes
Osteoglossidae
2
Uncommon
herring
Clupeiformes
Clupeidae
2
Extremely common
herring
Ellimmichthyiformes
Ellimmichthyidae
1
Common
Notogoneus
 
Gonorynchiformes
Gonorynchidae
1
Uncommon
Notogoneus osculus
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.