Paleobiota of the Morrison Formation
Most of the fossils occur in the green siltstone beds and lower sandstones, relics of the rivers and floodplains of the Jurassic period.
Dayvaultia[5] D. tetragona Henry Mountains of Utah (Brushy Basin Member) "Three-dimensional casts and partially permineralized small cones".
Although the paleoclimate of the Morrison formation was semiarid with only seasonal rainfall, there were enough bodies of water to support a diverse ichthyofauna.
[10] Single tooth fossil of pycnodont fish is represented from Dinosaur National Monument in Utah,[12] found in stratigraphic zone 4.
Hulettia[13] H. hawesi[14] Colorado A small fish of the division Halecostomi about 7.6 cm in length and 5g of live mass which probably preferred quiet water.
[15] Morrolepis[13] M. schaefferi[16] Colorado A coccolepidid "palaeoniscoid" with forward-set eyes positioned past the front end of the lower jaw.
Despite the erection of multiple new names, only two frog species are currently recognised from the Morrison: Enneabatrachus hechti[19] and Rhadinosteus parvus.
[20] 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.
[18] Iridotriton[13] I. hechti Utah, Brushy Basin[25] A basal salamandroid closely related to today's advanced salamanders.
Brushy Basin Member Most of the skull and postcranium A small-bodied eusphenodontian, and one of the most complete rhynchocephalian taxa yet known from North America.
Numerous squamate remains have been found in the sediments of the Morrison Formation, most commonly at sites in Utah, Colorado and Wyoming.
[27][28][29] The first squamates to be reported from the Morrison Formation were Paramacellodus and Dorsetisaurus, which were described from Wyoming's Quarry 9 by Don Prothero and Richard Estes.
[27] Later remains would include Diablophis, originally described as a species of Parviraptor by Susan Evans in 1996[30] but subsequently moved to the new genus Diablophis by Michael Caldwell et al. in 2015, with extra material also being reported from Utah's Cisco Mammal Quarry, and Schillerosaurus, originally described as "Schilleria" and reported from Dinosaur National Monument by Evans and Dan Chure in 1999.
[31] Two later additions to the Morrison's squamate assemblages are Eoscincus and Microteras, two scincomorph lizards found at Dinosaur National Monument and Como Bluff's Quarry 9, respectively.
All squamates might have been prey for the larger predators of the Morrison Formation, including the abundant theropod dinosaurs and crocodilians.
Diablophis[29] D. gilmorei Fruita Palaeontological Area, Colorado and Cisco Mammal Quarry, Utah (Brushy Basin Member) Broken skull material including a right maxilla, mandible and dentary.
Microteras[28] M. borealis Quarry 9 at Como Bluff, Wyoming (Brushy Basin Member) A partial skull consisting of an associated maxilla and braincase.
Fruita Palaeontological Area & Rainbow Park, Colorado and Quarry 9 at Como Bluff, Wyoming (Brushy Basin Member) Numerous specimens including jaws, skulls, osteoscutes, trunk vertebrae and hindlimbs.
[34] Schillerosaurus[13][35] S. utahensis [36][31] Dinosaur National Monument, Utah (Brushy Basin Member) Part and counterpart of a partial dissociated skeleton and a few limb bone fragments.
[36] Squamata[31] Indeterminate Dinosaur National Monument, Utah (Brushy Basin Member) Multiple specimens including fragmentary and disarticulated skeletons.
[38] Dorsetochelys[13] D. buzzops Glyptops[13] G. plicatulus[38] Colorado and Wyoming, Brushy Basin member[38] Several shells, skulls, and partial skeletons.
Pterosaurs are very uncommon fossils in the Morrison, because the fragility of their thin walled bones often prevented their remains from being preserved.
[48] Morrison pterosaurs probably lived on fish, insects and scavenged dinosaur carcasses, or even foraged for prey, and actively hunted;[48] they are fairly ecologically diverse, ranging from small hawking insectivore Mesadactylus to the raptorial Harpactognathus.
While relatively few pterosaur genera are named from the Morrison Formation, fragmentary material that is not referrable to the genus level suggests the presence of dsungaripteroids, ctenochasmatids, dimorphodontids, and more tentatively wukongopterids and pteranodontians.
[53] Many types of mammaliaform cynodonts, mostly early mammals, are known from the Morrison; almost all of them were small sized animals, though occupying a very large variety of ecological niches, from the more rodent-like multituberculates to the carnivorous eutriconodonts (including the possibly volant Triconolestes) to the anteater-like Fruitafossor.
Docodonts included the common genus Docodon, represented by D. victor, D. striatus, and D. superbus, and Peraiocynodon sp.
Multituberculates, a common type of early mammal, were represented by Ctenacodon serratus, C. laticeps, C. scindens, Glirodon grandis, Morrisonodon brentbaatar, Psalodon fortis, ?P.
Triconodonts present included Amphidon superstes, Aploconodon comoensis, Comodon gidleyi, Priacodon ferox, P. fruitaensis, P. gradaevus, P. lulli, P. robustus, Triconolestes curvicuspis, and Trioracodon bisulcus.
Finally, two families of Dryolestoidea were present: Paurodontidae, including Comotherium richi, Euthlastus cordiformis, Paurodon valens, and Tathiodon agilis; and Dryolestidae, including Amblotherium gracilis, Dryolestes obtusus (common genus), D. priscus, D. vorax, Laolestes eminens, L. grandis, and Miccylotyrans minimus.
Comodon[13] C. gidleyi Wyoming, Brushy Basin member An amphilestid eutriconodont slightly larger in size than Aploconodon.
