The Morrison Formation is a distinctive sequence of Late Jurassic sedimentary rock that is found in the western United States, which has a wide assortment of taxa represented in its fossil record, including dinosaur fossils in North America. It is composed of mudstone, sandstone, siltstone and limestone and is light grey, greenish gray, or red. Most of the fossils occur in the green siltstone beds and lower sandstones, relics of the rivers and floodplains of the Jurassic period.
(mostly from Foster [2003]; the higher-level classifications will vary as new finds are made.
Plants
Gnetales
Invertebrates
Arthropods
Vertebrates
Fish
Although the paleoclimate of the Morrison formation was semiarid with only seasonal rainfall, there were enough bodies of water to support a diverse ichthyofauna. Although abundant, fish remains are constrained to only certain locations within the formation. Microvertebrate sites in Wyoming are dominated by fish remains. Indeterminate ray-finned fish remains have been recovered from Ninemile Hill and a microvertebrate site in the Black Hills. Found in stratigraphic zones 2, 4, and 5. Morrison actinopterygians generally have no close modern relatives. The Wyoming microvertebrate remains are extracted from the sediment by screenwashing. Paleoniscoid remains are geographically present in the western part of Colorado, where remains have been recovered from "a level above the Mygatt-Moore Quarry." Largely complete remains of small individuals have been consistently recovered for over 15 years. Single tooth fossil of pycnodont fish is represented from Dinosaur National Monument in Utah, found in stratigraphic zone 4. Dipnoan remains found at a fossil site not far from Cañon City, Colorado. Remains usually in a state of rather complete preservation. Halecostome remains are geographically present in the western part of Colorado, where remains have been recovered from "a level above the Mygatt-Moore Quarry." Largely complete remains of small individuals have been consistently recovered for over 15 years. Amiid remains found in stratigraphic zones 2, 3, and 4. Found at a fossil site not far from Cañon City, Colorado. Remains usually in a state of rather complete preservation.
{ | class="wikitable" align="center" width="100%" |- ! Name ! Species ! Locality ! Material ! Notes ! Images |- | rowspan=5 | Ceratodus | C. fossanovum | | | rowspan=4 | A lungfish genus whose members ranged from 1 to 2 m in length and weights of up to 79 pounds, with most Morrison lungfish being on the smaller end of that range. These species are believed to have had similar diets to extant lungfish like the physically similar modern genus Neoceratodus. | rowspan=10 |
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C. ?frazieri
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C. guentheri
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C. robustus
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Indeterminate. | Brushy Basin and Saltwash members | | Represented by tooth plates. |- | Hulettia | H. hawesi | Colorado | | A small fish of the division Halecostomi about 7.6 cm in length and 5g of live mass which probably preferred quiet water. Its fossils prominently preserve its thick interlocking scales. |- | cf. Leptolepis | N/A | Colorado | Known only from a single nearly complete skeleton found at Rabbit Valley. Found in stratigraphic zone 5. | A 13 cm (5 inch) fish that was deeper bodied than its co-occurring contemporaries Morrolepis and Hulettia. The Morrison cf. Leptolepis probably had a live mass of about 37g. It is the only teleost fish known from the formation and was morphologically more highly derived than other Morrison fish. It is believed to have fed on contemporary fish and small invertebrates. |- | Morrolepis | M. schaefferi<ref name="foster-morrolepis">Foster, J. (2007). "Morrolepis schaefferi." pp. 131-132.</ref> | Colorado | | A coccolepidid "palaeoniscoid" with forward-set eyes positioned past the front end of the lower jaw. It had a tall dorsal fin set far back on the body and an asymmetrical caudal fin. Adult specimens would reach about 20 cm in length and 113 g (4 oz) in mass. |- | Potamoceratodus| P. guentheri| Colorado | | Once thought to be a species of Ceratodus. |- |}