The Morrison Formation is a distinctive sequence of Upper Jurassicsedimentary rock that is found in the western United States, which has been the most fertile source of 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.
"[Twenty-five to thirty] disarticulated skull elements, some with associated postcrania, approximately [ten] partial, articulated skeletons, juvenile to adult."[18]
A member of Camptosauridae. Junior synonyms include Camptosaurus browni, C. medius, and C. nanus.
Multiple Dinehichnus trackways have been discovered. The tracks run parallel to one another, indicating that the trackmaker was at least somewhat of a social animal.[6]
Dinehichnus are attributed to dryosaurids. The tracks preserve feet characterized by widely splayed toes and that are rotated somewhat toward the midline of the trackmaker's body. Each track is accompanied by "distinct ... heel impressions".[6]
The remains of many individuals have been uncovered, with some sites containing hundreds of bones from Dryosaurus of multiple age groups.[23]
A large dryosauridiguanodont up to 2.4 m (7.9 feet) long and 114 kg (251 lbs) in weight. It was physically similar to Othnielosaurus, although larger and with more derived teeth.[24]
A 2 partial skeletons, one a juvenile, and 2 additional fragmentary specimens.
A large dryosauridiguanodont up to 2.4 m (7.9 feet) long and 114 kg (251 lbs) in weight. It was physically similar to Othnielosaurus, although larger and with more derived teeth.[24]
Eggshell present in great abundance at the so-called "Young Egg Locality" which seems to have been a dinosaur nesting ground.[28] Congeneric eggshell fossils are found at additional Colorado sites including the Fruita Paleontological Area, the Uravan Locality and Garden Park.[28]
P. coloradensis is described by John Foster as being "of the prismatic basic type,"[28] with subspherical eggs about 10 cm (4 inches) in diameter.[29] This oospecies has been attributed to "hypsilophodontid" dinosaurs, although a lack of associated embryo material currently makes confirming the egg-layer's identity impossible.[28]
A polacanthinenodosaur known from reasonably complete fossil remains. Its skull measures 29 centimeters (11 in) in length, and its total body length is an estimated 3 to 4 meters (9.8 to 13.1 ft.). It may have weighed as much as 1 tonne (2,200 lb.).[30]
"Skull fragments, portions of [three] skeletons, [and] other postcrania."[33]
Both the first ankylosaur discovered in the formation and the first known North American Jurassic ankylosaur.[34] It probably weighed 500 kg (1,102 lbs) in life.[34]
A dacentrurinaestegosaurid physically similar to Stegosaurus stenops but with much larger tail spines.[37] It is also similar to Kentrosaurus in having long dermal spikes on the caudal region.[35] The thighbone length was determined at 1082 millimeters. The longest spike was 86 centimeters long. Its point was broken and it is estimated the original length of the bone core at 985 millimeters. In 2019, the genus Alcovasaurus was considered a junior synonym of Miragaia[38]
A stegosaurine stegosaurid that was slightly smaller and more primitive than Stegosaurus itself. H. mjosi had a broader skull and longer, lower plates. Considered by some to be a species of Stegosaurus
Stegopodus represent only a portion of the Morrison's stegosaur tracks, which are already rare and generally only preserve the animal's hind feet.[40]
Stegosaur tracks which record front feet with five digits and hind feet with three weight-bearing digits.[40] The general morphology of the tracks fit scientific predictions made eight years in advance of the erection of Stegopodus.[40]
Several caudal vertebrae and assorted fragmentary postcranial elements.[41]
S. armatus is both the first Stegosaurus to be discovered and the type species.[42] Its type specimen is poorly preserved, incomplete, and lacks diagnostic features.[41] It has been considered dubious, with S. stenops as the neotype species for the genus.[41]
Several postcranial elements, including a possible shoulder spike.[41]
Often considered synonymous with S. stenops,[46] it may be distinct. Potentially has a shoulder spike, otherwise unknown in Stegosaurus, despite presence in relatives.[41]
Several partial skeletons, including a partial braincase.[41]
S. ungulatus had longer limbs and comparatively smaller plates than the better known S. stenops.[47] Although formerly portrayed with eight tail spikes, it is now known to have had the typical four.[48] Possibly synonymous with S. stenops.[49]
By the late Morrison, gigantic diplodocids (or similar species) 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.[54]
Historically considered to be an allosaurid close to or a species of Allosaurus, but re-evaluated as a dubious, chimeric genus of saurischian, likely a diplodocid sauropod.[80]
Camarasaurs reached an adult size of about 18 m (60 ft) in length.[81]C. annae junior synonym of C. lentus. C. lewisi was originally described as Cathetosarus lewisi and was later sunk into Camarasaurus, until being considered valid once again in 2013.
Multiple vertebrae, teeth and incomplete forelimb material.[85]
Previously recovered as a diplodocid, now recovered as a macronarian[85] Type material fragmentary, but recent rediscovery of type locality has discovered more material.[86]
Indeterminate theropod remains have been recovered in Utah, with indeterminate ceratosaur remains formerly considered referable to Elaphrosaurus recovered in Colorado. Indeterminate theropod tracks have been recovered from both Utah and Arizona.[87]
Colorado, New Mexico, Oklahoma, South Dakota, Utah and Wyoming, Brushy Basin member[16][50][17][66][9][88]
"At least [three] complete skulls, many partial skulls and skull elements, many partial and complete skeletons representing at least 60 individuals."[89] It was the most common large carnivore in the area.[90][91][92]
Large ceratosaurs grew to lengths of about 6–7 meters (20–23 ft.) in length with large nasal horns on their snouts as well as two smaller horns above the eyes.
Previously referred to Elaphrosaurus,[101][102][103] these remains are probably not referable to that genus and are best considered indeterminate beyond Ceratosauria.[104]
Morrison ornithopod trace fossils are represented by three toed tracks which are generally small.[6] The toes of Morrison ornithopod tracks are usually more widely splayed than the theropod tracks preserved in the formation.[6]
Stegosaurs
Stegosaur tracks were first recognized in 1996 from a hindprint-only trackway discovered at the Cleveland-Lloyd quarry, which is located near Price, Utah.[40]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.[40] 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.[40] 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.[40] Since the erection of Stegopodus, more trackways have been found, however none have preserved traces of the front feet, and stegosaur traces remain rare.[40]
Theropods
Indeterminate theropod tracks have been recovered from both Utah and Arizona.[87]
Footnotes
^Mateus, O. 2006. Late Jurassic dinosaurs from the Morrison Formation, the Lourinhã and Alcobaça Formations (Portugal), and the Tendaguru Beds (Tanzania): a comparison. New Mexico Museum of Natural History and Science Bulletin. 36:223-231.
^Hendrickx, C, Mateus O. 2014. Torvosaurus gurneyi n. sp., the largest terrestrial predator from Europe, and a proposed terminology of the maxilla anatomy in nonavian theropods, 03. PLOS ONE. 9:e88905., Number 3
^Mateus, O., & Antunes M. T. (2000). Ceratosaurus sp. (Dinosauria: Theropoda) in the Late Jurassic of Portugal. Abstract volume of the 31st International Geological Congress, Rio de Janeiro, Brazil
^Mateus, O. (2007). Notes and review of the ornithischian dinosaurs of Portugal. Journal of Vertebrate Paleontology. 27, 114A-114A., Jan: Society of Vertebrate Paleontology
^Mateus, O, Walen A, Antunes MT. 2006. The large theropod fauna of the Lourinhã Formation (Portugal) and its similarity to the Morrison Formation, with a description of a new species of Allosaurus. New Mexico Museum of Natural History and Science Bulletin. 36:123-129.
^ abcdefgh"Walk and Don't Look Back: The Footprints; Ornithopods" Foster (2007) pg. 238
^ abcdefg"Dinosaur distribution (Late Jurassic; North America; Oklahoma)." Weishampel, et al. (2004). Heading at end of Pg. 544, content starts at the beginning of pg. 545.
^"Table 19.1," in Weishampel, et al. (2004). Page 415.
^Jurassic West Foster (2007) pg. 219 attributes most Drinker nisti specimens to Como Bluff, which is in Wyoming. See figure 1.2 on Jurassic West page 6.
^"Table 18.1," in Weishampel, et al. (2004). Page 394.
^ abcdefKenneth Carpenter; Peter M. Galton (2018). "A photo documentation of bipedal ornithischian dinosaurs from the Upper Jurassic Morrison Formation, USA". Geology of the Intermountain West. 5: 167–207.
^ ab"Jurassic Knights: The Ankylosaur Dinosaurs; Gargoyleosaurus parkpinorum," Foster (2007) pp. 216
^"Table 17.1," in Weishampel, et al. (2004). Page 364.
^Tremaine, K., D'Emic, M., Williams, S., Hunt-Foster, R.K., Foster, J., and Mathews, J., (2015), Paleoecological implications of a new specimen of the ankylosaur Mymoorapelta maysi from the Hanksville-Burpee Quarry, latest Jurassic (Tithonian) Morrison Formation (Brushy Basin Member) [abs.]: Journal of Vertebrate Paleontology Program and Abstracts, p. 226.
^"Table 17.1," in Weishampel, et al. (2004). Page 366.
^ ab"Jurassic Knights: The Ankylosaur Dinosaurs; Mymoorapelta maysi," Foster (2007) pp. 215-216
^ abMaidment, Susannah C.R.; Woodruff, D. Cary; Horner, John R. (2018). "A new specimen of the ornithischian dinosaur Hesperosaurus mjosi from the Upper Jurassic Morrison Formation of Montana, U.S.A., and implications for growth and size in Morrison stegosaurs". Journal of Vertebrate Paleontology. 38 (1). e1406366. Bibcode:2018JVPal..38E6366M. doi:10.1080/02724634.2017.1406366. hdl:10141/622747. S2CID90752660.
^ abcdefghij"Walk and Don't Look Back: The Footprints; Stegosaurs" Foster (2007) pg. 238
^Carpenter, Kenneth. (1998). Armor of Stegosaurus stenops, and the taphonomic history of a new specimen from Garden Park, Colorado. Modern Geology, 23, 127-144.
^Galton PM, Upchurch P (2004). "Stegosauria". In Weishampel DB, Dodson P, Osmólska H. The Dinosauria (2nd Edition). University of California Press. p. 361.
^"Roof Lizards: The Stegosaur Dinosaurs; Stegosaurus ungulatus," Foster (2007) pp. 212-213.
^Maidment, Susannah C.R.; Norman, David B.; Barrett, Paul M.; Upchurch, Paul (2008). "Systematics and phylogeny of Stegosauria (Dinosauria: Ornithischia)". Journal of Systematic Palaeontology. 6 (4): 367–407. doi:10.1017/S1477201908002459. S2CID85673680.
^ abcd"Dinosaur distribution (Late Jurassic; North America; New Mexico)." Weishampel, et al. (2004). Pg. 544.
^ abHarris, J.D. and Dodson, P. (2004). "A new diplodocoid sauropod dinosaur from the Upper Jurassic Morrison Formation of Montana, USA." Acta Palaeontologica Polonica, 49(2): 197–210.
^ abcde"Table 13.1," in Weishampel, et al. (2004). Page 266.
^ ab"Table 13.1," in Weishampel, et al. (2004). Page 262.
^Harris, J.D. and Dodson, P. (2004). "A new diplodocoid sauropod dinosaur from the Upper Jurassic Morrison Formation of Montana, USA." Acta Palaeontologica Polonica 49 (2): 197–210.
^ ab"Table 13.1," in Weishampel, et al. (2004). Page 265.
^Foster, John R.; Peterson, Joseph E. (September 2016). "First report of Apatosaurus (Diplodocidae: Apatosaurinae) from the Cleveland-Lloyd Quarry in the Upper Jurassic Morrison Formation of Utah: Abundance, distribution, paleoecology, and taphonomy of an endemic North American sauropod clade". Palaeoworld. 25 (3): 431–443. doi:10.1016/j.palwor.2015.11.006. ISSN1871-174X.
^ abBerman DS, McIntosh JS. 1978. Skull and relationships of the Upper Jurassic sauropod Apatosaurus (Reptilia, Saurischia). Bulletin of the Carnegie Museum of Natural History 8:1–35.
^ abc"Dinosaur distribution (Late Jurassic; North America; South Dakota)." Weishampel, et al. (2004). Pg. 545.
^"Barosaurus lentus". National Park Service. U. S. Department of the Interior. Retrieved 21 March 2021.
^ ab"Table 13.1," in Weishampel, et al. (2004). Page 264.
^"Diplodocus longus". National Park Service. U. S. Department of the Interior. Retrieved 21 March 2021.
^Lovelace, David M.; Hartman, Scott A.; Wahl, William R. (2007). "Morphology of a specimen of Supersaurus (Dinosauria, Sauropoda) from the Morrison Formation of Wyoming, and a re-evaluation of diplodocid phylogeny". Arquivos do Museu Nacional. 65 (4): 527–544.
^Gillette, D.D. (1991). "Seismosaurus halli, gen. et sp. nov., a new sauropod dinosaur from the Morrison Formation (Upper Jurassic/Lower Cretaceous) of New Mexico, USA". Journal of Vertebrate Paleontology. 11 (4): 417–433. doi:10.1080/02724634.1991.10011413.
^Lucas, S.G.; Spielman, J.A.; Rinehart, L.A.; Heckert, A.B.; Herne, M.C.; Hunt, A.P.; Foster, J.R.; Sullivan, R.M. (2006). "Taxonomic status of Seismosaurus hallorum, a Late Jurassic sauropod dinosaur from New Mexico". In Foster, J.R.; Lucas, S.G. (eds.). Paleontology and Geology of the Upper Morrison Formation. New Mexico Museum of Natural History and Science (bulletin 36). pp. 149–161. ISSN1524-4156.
^ abcTschopp, E.; Mateus, O. V. (2013). "The skull and neck of a new flagellicaudatan sauropod from the Morrison Formation and its implication for the evolution and ontogeny of diplodocid dinosaurs". Journal of Systematic Palaeontology: 1. doi:10.1080/14772019.2012.746589 edit
^Chure (1995). A reassessment of the gigantic theropod Saurophagus maximus from the Morrison Formation (Upper Jurassic) of Oklahoma, USA. Sixth Symposium on Mesozoic Terrestrial Ecosystems and Biota. 103-106.
^ ab"Dinosaur distribution (Late Jurassic; North America; 'Utah' and 'Arizona')." Weishampel, et al. (2004). Pg. 544.
^ abLoewen, Mark A.; Sampson, Scott D.; Carrano, Matthew T.; Chure, Daniel J. (2003). "Morphology, taxonomy, and stratigraphy of Allosaurus from the Upper Jurassic Morrison Formation". Journal of Vertebrate Paleontology. 23 (3): 72A. doi:10.1080/02724634.2003.10010538. S2CID220410105.
^"Table 4.1," in Weishampel, et al. (2004). Page 75.
^Chure DJ, Loewen MA. 2020. Cranial anatomy of Allosaurus jimmadseni, a new species from the lower part of the Morrison Formation (Upper Jurassic) of Western North America. PeerJ 8:e7803 https://doi.org/10.7717/peerj.7803
^ abc"Table 3.1," in Weishampel, et al. (2004). Page 49.
^Galton, 1982. Elaphrosaurus, an ornithomimid dinosaur from the Upper Jurassic of North America and Africa. Paläontologische Zeitschrift. 56, 265-275.
^Pickering, 1995a. Jurassic Park: Unauthorized Jewish Fractals in Philopatry. A Fractal Scaling in Dinosaurology Project, 2nd revised printing. Capitola, California. 478 pp.
^Chure, 2001. The second record of the African theropod Elaphrosaurus (Dinosauria, Ceratosauria) from the Western Hemisphere. Neues Jahrbuch für Geologie und Paläontologie - Monatshefte. 2001(9), 565-576.
^Carrano and Sampson, 2008. The phylogeny of Ceratosauria (Dinosauria: Theropoda). Journal of Systematic Palaeontology. 6, 183-236.
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