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).