GREEN RIVER FORMATION
The Green River Formation of Utah-Colorado-Wyoming is
famous for having vast oil shale deposits and for having exquisitely-preserved
fossils. Fossil Butte
National Monument in southwestern Wyoming preserves and displays some of
these high-quality fossils. Leaves and fish are the most common large
fossils in the Fossil Lake Basin of the Green River Fm.
Stratigraphy: Fossil Butte Member, Green River Formation, upper Wasatchian Stage
(Wa4)/Ypresian Stage/Lostcabinian, Lower Eocene.
Knightia eocaena (Jordan, 1907) - complete fossil herring (9.1 cm
across) in marlstone from the Fossil Butte Member’s “Eighteen-Inch Layer”,
southwestern Wyoming, USA.
Classification: Animalia, Chordata, Vertebrata, Actinopterygii,
Clupeiformes, Clupeidae.
Mioplosus labracoides (above & below; 16.7 cm across) - complete fossil
perch in marlstone from the Fossil Butte Member’s “Eighteen-Inch Layer”,
southwestern Wyoming, USA. Mioplosus was a predator, mainly
feeding on the common smaller fish Knightia. The Mioplosus
shown here has a partially digested Knightia visible in its stomach -
most of the Knightia’s vertebral column and the proximal ribs are
still present. The brownish area just below the Mioplosus backbone
may be a remnant of the Knightia’s head, but I’m not sure.
Classification: Animalia, Chordata, Vertebrata, Actinopterygii,
Perciformes, Percidae
Mioplosus labracoides (same specimen as above; field of view ~4.6 cm
across) - close-up of partially digested Knightia in the stomach of a Mioplosus.
Mass fish mortality - fossiliferous marlstone slab (~28.5 cm across) from
the Fossil Butte Member’s “Eighteen-Inch Layer” having many small Knightia
(herring) and one large Mioplosus (perch).
Priscacara liops Cope, 1877 - fossil perch in marlstone from
southwestern Wyoming, USA (FMNH PP 53399, Field Museum of Natural History,
Chicago, Illinois, USA).
Classification: Animalia, Chordata, Vertebrata, Actinopterygii,
Perciformes, Priscacaridae
Green River Formation bird - unidentified bird species from the Fossil Butte
Member in southwestern Wyoming, USA (FMHH PA 778, Field Museum of Natural
History, Chicago, Illinois, USA).
Classification: Animalia, Chordata, Vertebrata, Aves
Borealosuchus wilsoni (Mook, 1959) - fossil crocodile from the Green River
Formation of southwestern Wyoming, USA
(FMNH PR 1674, Field Museum of Natural History, Chicago, Illinois, USA).
Classification: Animalia, Chordata, Vertebrata, Reptilia,
Crocodyliformes, Neosuchia, Eusuchia, Crocodylia
Plant branch & Knightia herring in marlstone from southwestern Wyoming, USA (FMNH PP
43943, Field Museum of Natural History, Chicago, Illinois, USA).
Sabalites powelli palm frond and fish in marlstone from southwestern
Wyoming, USA (FMNH PP 53399, Field Museum of Natural History, Chicago,
Illinois, USA).