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.

Plants The Morrison Formation is devoid of flowering plants; during the Jurassic, the Earth was dominated by ferns, seed ferns, and a wealth of gymnosperms—such as cycads, ginkgos, and conifers. Vegetation varied from river-lining forests of conifers, tree ferns, and ferns (gallery forests), to fern savannas with occasional trees such as the Araucaria-like conifer Brachyphyllum.

Conifers Genus Species Locality Material NotesMesembrioxylonM. carteriiProtocupressinoxylonP. medlyniiBrachyphyllumB. rechtenii B. spSequoiaS.spAraucaria Cf. A. sp A. delevoryasii

Ginkgos Genus Species Locality Material NotesGinkgoG. sp

Cycadophyta and relatives Genus Species Locality Material NotesNilssoniaN. comptaZamitesZ. arcticusCycadolepisC. sp

Gnetales Genus Species Locality Material NotesBassithecaB. hoodiorumColorado and Utah (Brushy Basin Member)More than 300 specimens, three dimensional calcitic casts of a two-seeded compound coneTentatively assigned as a gnetale, with some attributes of the cones pointing towards a close relation with the extant genus Ephedra. DayvaultiaD. tetragonaHenry Mountains of Utah (Brushy Basin Member)"Three-dimensional casts and partially permineralized small cones".A gnetale with close affinities to Cretaceous and modern genera.

Invertebrates

Arthropods Trace fossils reported from the Morrison Formation are indicative of greater diversity of arthropods (especially insects) than recorded by body fossils. Bone modifications likely produced by dermestid beetles were reported in vertebrate fossils from Wyoming and Colorado.

Name Species Locality Material NotesCambaridaeIndeterminateA crayfishColeopteraIndeterminateUtahIsolated elytra.DecapodaUtahA specimen preserved with structures similar to eyes on stalks, antennae and a cheliped.Possibly a freshwater hermit crab.Eopolis E. ekdalei Utah, Brushy Basin member Nests produced by social insects, possibly termites. MorrisonnepaM. jurassicaUtah A hemipteran belonging to the group Nepomorpha.ParapleuritesD. M. Smith, M. A. Gorman, J. D. Pardo and B. J. Small. 2011. First fossil Orthoptera from the Jurassic of North America. Journal of Paleontology 85(1):102-105P. morrisonensisColorado a forewing. A Locustopsid orthopteranSpinicaudataUtahAt least 10 specimens preserved as shells. Tektonargus T. kollaspilus Colorado, Brushy Basin member Five specimens were reported in the original description of the ichnogenus.

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,Foster, J. (2007). "Pycnodontoidea." Jurassic West: The Dinosaurs of the Morrison Formation and Their World. Indiana University Press. p. 135. 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.Foster, J. (2007). "Appendix." Jurassic West: The Dinosaurs of the Morrison Formation and Their World. Indiana University Press. pp. 327-329. Found at a fossil site not far from Cañon City, Colorado. Remains usually in a state of rather complete preservation.

Name Species Locality Material Notes Images Ceratodus C. fossanovumFoster, J. (2007). "The Forgotten Aquatic Denizens: The Fish." pp. 129-131.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. C. ?frazieri C. guentheri C. robustus Indeterminate.Brushy Basin and Saltwash membersRepresented by tooth plates. "Hulettia" "H. hawesi"Foster, J. (2007). "Hulettia hawesi." p. 132-134.ColoradoA small fish, originally considered as a member of 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. Later study question its assignment to genus Hulettia, and suggested that it would be a semionotid instead. cf. Leptolepis N/AColoradoKnown only from a single nearly complete skeleton found at Rabbit Valley.Foster, J. (2007). "cf. Leptolepis." p. 135. 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. schaefferiFoster, J. (2007). "Morrolepis schaefferi." pp. 131-132.ColoradoA 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. guentheriColoradoOnce thought to be a species of Ceratodus.PurgotybarisP. fosteriUtahA regurgitalite containing frog and salamander bones, probably produced by an amioid fish. A hybodont? IndeterminateUtah Known from a dorsal spine.

Amphibians

Frogs are known from several sites in the Morrison Formation, but are not particularly well represented.Foster, J. (2007). "Anura (Frogs)." pp. 135-136. The history of Morrison anuran discoveries began with the recovery of remains from Quarry 9 near Como Bluff, Wyoming. The new genus Eobatrachus was erected for some of these remains by O. C. Marsh, but the material was later considered non-diagnostic. Decades later another dubious anuran genus, Comobatrachus, was erected based on additional fragmentary remains. Despite the erection of multiple new names, only two frog species are currently recognised from the Morrison: Enneabatrachus hechti and Rhadinosteus parvus.

In addition to formally named taxa, indeterminate anuran remains have been recovered from Morrison strata in Colorado, Wyoming, and Utah, with the best specimens found in Dinosaur National Monument and Quarry 9. Stratigraphically speaking, indeterminate anurans have been found in stratigraphic zones 2 and 4. Indeterminate anurans with remains diagnostic down to the family level have also been reported from the Morrison, with pelobatids being represented by the ilium of an unnamed and indeterminate species, which was recovered from Quarry 9.Foster, J. (2007). "Pelobatidae indet." p. 137. Pelobatids are present in stratigraphic zones 5 and 6.

Indeterminate salamander remains are present in stratigraphic zones 2, 4, and 5. A distinctive type of salamander known only as Caudata B is present in stratigraphic zone 6.

Name Species Locality Material Notes Comobatrachus C. aenigmaticus Wyoming, Brushy Basin member A partial right humerus.Evans, S. E. and Milner, A. R. (1993). Frogs and salamanders from the Upper Jurassic Morrison Formation (Quarry Nine, Como Bluff) of North America. Journal of Vertebrate Paleontology 13(1):24-30 A dubious genus of prehistoric frog erected by O. C. Marsh to house fragmentary remains recovered from Reed's Quarry 9 near Como Bluff Wyoming. Along with Eobatrachus it was among the earliest frog remains from the formation, although the two dubious genera were erected decades apart. ComonecturoidesFoster, J. (2007). "Caudata (Salamanders)" p. 138. C. marshi Wyoming, Brushy Basin member Represented by a single femur. Considered a nomen dubium because the name is based on non-distinctive remains which cannot be classified in detail. EnneabatrachusFoster, J. (2007). "Table 2.1: Fossil Vertebrates of the Morrison Formation." pp. 58-59. E. hechtiFoster, J. (2007). "Enneabatrachus hechti" p. 137.Utah and WyomingFoster, J. (2007). "Enneabatrachus hechti" p. 137. Note that Dinosaur National Monument is in Utah, see ibid. pg. 6.A small discoglossid frog whose live weight would have only been a few grams. Eobatrachus E. agilis Wyoming, Brushy Basin member A partial right humerus. A dubious genus of prehistoric frog erected by O. C. Marsh to house fragmentary remains recovered from Reed's Quarry 9 near Como Bluff Wyoming. Along with Comobatrachus it was among the earliest frog remains from the formation, although the two dubious genera were erected decades apart. Iridotriton I. hechtiUtah, Brushy BasinEvans, S. E., Lally, C., Chure, D. C., Elder, A., & Maisano, J. A. (2005). A late Jurassic salamander (Amphibia: Caudata) from the Morrison formation of north America. Zoological Journal of the Linnean Society, 143(4), 599-616.A partial skull and incomplete postcranial skeleton.A basal salamandroid closely related to today's advanced salamanders. Rhadinosteus R. parvusFoster, J. (2007). "Rhadinosteus parvus." p. 137.UtahKnown from several slabs of rock which contain multiple partial specimens in association.A pipoid and possible rhinophrynid, Rhadinosteus parvus was only about 42 mm (1.6 inches) long in life.

Sphenodonts

Name Species Locality Material NotesImagesEilenodonE. robustusColoradoSeveral fragmentary skull, mandible, and tooth elements.A herbivorous eilenodontine of relatively large size. Opisthias O. rarusColorado, Utah and Wyoming, Brushy Basin memberSeveral skulls and partial skeletons.An opisthodontian sphenodontianOpisthiamimusO. gregoriNorthern Wyoming, possibly west-central Colorado. Brushy Basin MemberMost of the skull and postcraniumA small-bodied eusphenodontian, and one of the most complete rhynchocephalian taxa yet known from North America.Theretairus T. antiquusWyoming, Brushy Basin memberA mandible.A small sphenodontian.SphenodontiaIndeterminateDinosaur National MonumentA crushed partial skull (DINO 16454)The specimen is undescribed. Although previously considered to have belonged to Opisthias or Theretairus, recent studies have doubted this referral, thus placing it as an indeterminate sphenodont.

Squamates