User:The Morrison Man/sandbox

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Paleobiota of the Morrison Formation
The Morrison Formation is a distinctive sequence of Late Jurassic sedimentary rock that is found in the western United States. It has a vast fossil record, with a wide assortment of taxa represented, including famous dinosaurs like Brachiosaurus, Allosaurus, Diplodocus and Stegosaurus. It is composed of mudstone, sandstone, siltstone and limestone and is light grey, greenish gray, or red in colour. Most of the fossils occur in the green siltstone beds and lower sandstones, relics of the rivers and floodplains of the Jurassic period.

The formation is split into three main members, these are the Salt Wash, Tidwell and Brushy Basin members. Other subdivisions exist in specific areas of the formation, like the Bluff Sandstone Member in the Four Corners region. The most well-studied of these are the Brushy Basin and contemporaneous members, from which most of the iconic Morrison Formation fauna hails.

The rocks of the Morrison Formation were deposited on top of those of the Sundance, Swift, Ralston Creek and Summerville formations, as the Sundance Sea receded to the north and the region became a vast floodplain, fed by rivers coming in from the south and west. Multiple formations also overlie the Morrison, including the ...

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, with microvertebrate sites in Wyoming especially being dominated by fish remains. Indeterminate remains of ray-finned fish have been recovered from Ninemile Hill and a microvertebrate site in the Black Hills. Morrison actinopterygians have been found in stratigraphic zones 2, 4, and 5, and 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. So far, Morrison pycnodontoids are represented by a single specimen from Dinosaur National Monument in Utah. Found in stratigraphic zone 4. Only a single specimen from Dinosaur National Monument in Utah has been recovered. Pycnodontoids were "deep-bodied and laterally compressed fish" whose tooth morphology suggest that they preyed on small contemporary invertebrates. They may have resembled modern butterfly fish. A single tooth is the only known remains. 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.

Amphibians
Frogs are known from several sites in the Morrison Formation, but are not particularly well represented. 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 illium of an unnamed and indeterminate species, which was recovered from Quarry 9. 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.

Squamates
Numerous squamate remains have been found in the sediments of the Morrison Formation, most commonly at sites in Utah, Colorado and Wyoming. A number of taxa have been described, coming from three different groups: anguimorph and scincomorph lizards and early snakes. 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. Later remains would include Diablophis, originally described as a species of Parviraptor by Susan Evans in 1996 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. 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. They were described by Chase Brownstein et al. in 2022. Indeterminate squamate remains have currently been described from Dinosaur National Monument.

The majority of modern-day scincomorph lizards are small insectivores that feed on a range of invertebrates. It is thought that their counterparts from the Morrison Formation would have occupied a similar niche due to their morphological similarities. Anguimorph lizards most likely hunted small vertebrates, and Diablophis is thought to have done so too. Prey items would have included the other squamates from the formation as well as its large diversity of small mammals. All squamates might have been prey for the larger predators of the Morrison Formation, including the abundant theropod dinosaurs and crocodilians.

Testudines
Turtles (Testudines) are very common fossils in the Morrison, due to their bony shells. The most common were Glyptops plicatus (very common) and Dinochelys whitei (also common, but not as common as Glyptops). Also present were Dorsetochelys buzzops and Uluops uluops.

Crurotarsans
Crocodiles of a variety of sizes and habitats were common Morrison animals. Cursorial mesosuchians, or small terrestrial running crocs, included Hallopus victor and Fruitachampsa callisoni. More derived crocodilians included Diplosaurus ferox, Amphicotylus, Hoplosuchus kayi, and Macelognathus vagans.

Pterosaurs
Pterosaurs are very uncommon fossils in the Morrison, because the fragility of their thin walled bones often prevented their remains from being preserved. Despite being uncommon they are geographically widespread; indeterminate pterosaur remains have been found in stratigraphic zones 2 and 4-6. In addition to indeterminate remains, several species have been identified from both the rhamphorhynchoids (long-tailed pterosaurs) and pterodactyloids (short-tailed pterosaurs). Since the 1970s and 80s, pterosaur finds have become more common, but are still rare. Most Morrison pterosaurs have been found in marine and shoreline deposits. Pterosaur tracks have been found in both the Tidwell and Saltwash members. Morrison pterosaurs probably lived on fish, insects and scavenged dinosaur carcasses, or even foraged for prey, and actively hunted; 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.

Ornithischians
The herbivorous ornithischian dinosaurs were diverse but not as common as sauropods in the Morrison. Fruitadens, previously known as the "Fruita Echinodon", was found to be a heterodontosaurid. Plate-backed stegosaurids included Hesperosaurus mjosi, Stegosaurus armatus, S. ungulatus, S. stenops, and Alcovasaurus longispinus. Armored dinosaurs that weren't stegosaurs were unknown in the formation until the 1990s. Two have been named: Gargoyleosaurus parkpinorum and Mymoorapelta maysi. Ornithopods, bipedal herbivores, came in several types. Small "hypsilophodonts" included Drinker nisti, Laosaurus celer, "L." gracilis, Nanosaurus agilis, Othnielia rex, and Othnielosaurus consors (all of which are now synonymous with Nanosaurus). Larger but similar-looking dryosaurids were represented by Dryosaurus altus and the camptosaurid Uteodon aphanoecetes, which is currently known only from Dinosaur National Monument. Still larger was the more common Camptosaurus dispar. Dryosaurids and camptosaurids were early iguanodonts, a group that would later spawn the duck-billed dinosaurs.

Morrison ornithopod trace fossils are represented by three toed tracks which are generally small. The toes of Morrison ornithopod tracks are usually more widely splayed than the theropod tracks preserved in the formation. Stegosaur tracks were first recognized in 1996 from a hindprint-only trackway discovered at the Clevland-Lloyd quarry, which is located near Price, Utah. Two years later, a new ichnogenus called Stegopodus was erected for another set of stegosaur tracks which were found near Arches National Park, also in Utah. Unlike the first, this trackway preserved traces of the forefeet. Fossil remains indicate that stegosaurs have five digits on the forefeet and three weight-bearing digits on the hind feet. From this, scientists were able to successfully predict the appearance of stegosaur tracks in 1990, six years in advance of the first actual discovery of Morrison stegosaur tracks. Since the erection of Stegopodus, more trackways have been found, however none have preserved traces of the front feet, and stegosaur traces remain rare.

Sauropods
Sauropods, the giant long-necked long-tailed four-legged herbivorous dinosaurs, are among the most common and famous Morrison fossils. A few have uncertain relationships, like "Apatosaurus" minimus (possibly a basal titanosauriform) and Haplocanthosaurus. Sauropods including Haplocanthosaurus priscus, H. delfsi, and the diplodocid Eobrontosaurus appeared in the early stages of the Morrison. The middle stages were dominated by familiar forms such as the Giraffe-like Brachiosaurus altithorax, which were uncommon, but related camarasaurids, like Camarasaurus supremus, C. grandis, C. lentus, and Cathetosaurus, were very common. Also common were long, low diplodocids, like Apatosaurus ajax, A. louisae, Brontosaurus excelsus, B. parvus, Barosaurus lentus, Diplodocus longus, D. carnegii, Galeamopus and Dyslocosaurus polyonychius.

By the late Morrison, gigantic diplodocids (or likely diplodocids) had appeared, including Diplodocus hallorum (formerly Seismosaurus), Supersaurus vivianae, Amphicoelias altus, and M. fragilimus. Smaller sauropods, such as Suuwassea emiliae from Montana, tend to be found in the northern reaches of the Morrison, near the shores of the ancient Sundance Sea, suggesting ecological niches favoring smaller body size there compared with the giants found further south.

Theropods
Theropod dinosaurs, the carnivorous dinosaurs, came in several different types. The less derived types, the ceratosaurs and megalosaurids, included Ceratosaurus nasicornis, C. dentisulcatus, C. magnicornis, Elaphrosaurus sp., and the megalosaur Torvosaurus tanneri (including Edmarka rex). Allosaurids included the common Allosaurus fragilis (including Epanterias amplexus), Allosaurus new species, A. lucasi, and giant Saurophaganax maximus (potentially included in Allosaurus?). Also a recently discovered dinosaur has turned out to be a new species, not Allosaurus. It's a proceratosaurid tyrannosauroid.

Indeterminate theropod remains have been recovered in Utah. Indeterminate theropod tracks have been recovered from both Utah and Arizona.

Mammaliaforms
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. Unclassified types include the digger Fruitafossor windscheffelia. 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. marshi, P. potens, and Zofiabaatar pulcher''. Triconodonts present included Amphidon superstes, Aploconodon comoensis, Conodon gidleyi, Priacodon ferox, P. fruitaensis, P. gradaevus, P. lulli, P. robustus, Triconolestes curvicuspis, and Trioracodon bisulcus.

Tinodontids were represented by Eurylambia aequicrurius (probably Tinodon), and Tinodon bellus (including T. lepidus). 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.

In 2009, a study by J. R. Foster was published which estimated the body masses of mammals from the Morrison Formation by using the ratio of dentary length to body mass of modern marsupials as a reference. Foster concludes that Docodon was the most massive mammaliaform genus of the formation at 141g and Fruitafossor was the least massive at 6g. The average Morrison mammal had a mass of 48.5g. A graph of the body mass distribution of Morrison mammal genera produced a right-skewed curve, meaning that there were more low-mass genera.