The Morrison Formation is a distinctive sequence of Upper Jurassic sedimentary rocks 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 gray, 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.
Fauna comparisons The fauna of the Morrison Formation is similar to the ones found in the coeval rocks of the Tendaguru Formation from Tanzania and Lourinhã and Alcobaça Formation from Portugal respectively.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. Some genera are shared between the Morrison and the Portuguese formations (Lourinhã and Alcobaça Formation), such as Torvosaurus, Ceratosaurus, Stegosaurus, and Allosaurus.
Ornithischians The herbivorous ornithischian dinosaurs were diverse but not as common as sauropods in the Morrison. Fruitadens, previously known as the "Fruita Echinodon", was a heterodontosaurid. Stegosaurs included Hesperosaurus mjosi, Stegosaurus (S. ungulatus and S. stenops), Alcovasaurus longispinus and possibly Miragaia longicollum. Ankylosaurs were unknown in the formation until the 1990s. Two have been named: Gargoyleosaurus parkpinorum and Mymoorapelta maysi. Small neornithischians included Nanosaurus agilis, Enigmacursor mollyborthwickae, Laosaurus (L. celer and L. gracilis), Drinker nisti, Othnielia rex, and Othnielosaurus consors (the last three of which are now considered synonymous with Nanosaurus). Ornithopods were represented by Dryosaurus (D. altus and D. elderae), Uteodon aphanoecetes, which is currently known only from Dinosaur National Monument, and the larger, more common Camptosaurus dispar. All of the aforementioned ornithopod genera were early iguanodonts, the group that gave rise to the duck-billed dinosaurs.
Neornithischians
Genus Species Locality Material Notes Images AnomoepusA. isp. Colorado"Walk and Don't Look Back: The Footprints; Ornithopods" Foster (2007) pg. 238 Anomoepus from the Morrison lack the handprint impressions found associated with earlier instances of the ichnogenus in New England Camptosaurus"Table 2.1: Fossil Vertebrates of the Morrison Formation" in Foster (2007) pp. 58-59.C. amplus"Fleet-Footed Plant Eaters: The Ornithopod Dinosaurs; Camptosaurus dispar," Foster (2007) pg. 220Wyoming Now known to be based on a theropod footC. aphanoecetes"Systematic Paleontology: Camptosaurus aphanoecetes" in "A New Species of Camptosaurus..." Carpenter and Wilson (2008), page 232.Utah, Brushy Basin memberReclassified as Uteodon C. browni Junior synonym of C. dispar C. dispar"Dinosaur distribution (Late Jurassic; North America; Utah)." Weishampel, et al. (2004). Pp. 543-544."Fleet-Footed Plant Eaters: The Ornithopod Dinosaurs; Camptosaurus dispar," Foster (2007) pp. 219-220Colorado, Oklahoma, Utah and WyomingTwenty-five to thirty disarticulated skull elements, some with associated postcrania, and approximately ten partial, articulated skeletons, all from juveniles and adults"Table 19.1," in Weishampel, et al. (2004). Page 415. A member of Ankylopollexia. Junior synonyms include Camptosaurus browni, C. medius, and C. nanus C. medius Junior synonym of C. dispar C. nanus Junior synonym of C. dispar DinehichnusD. socialis Utah, Saltwash member Multiple trackways have been discovered. The tracks run parallel to one another, indicating that the trackmaker was at least a somewhat social animal Dinehichnus are attributed to dryosaurids. The tracks preserve feet characterized by widely splayed toes that are rotated somewhat towards the midline of the trackmaker's body. Each track is accompanied by "distinct heel impressions" Drinker"Fleet-Footed Plant Eaters: The Ornithopod Dinosaurs; Drinker nisti," Foster (2007) pg. 219 D. nisti WyomingJurassic 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. "Partial skull and postcranial skeleton.""Table 18.1," in Weishampel, et al. (2004). Page 394. Junior synonym of NanosaurusKenneth 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. Dryosaurus D. altusColorado and Wyoming, Brushy Basin member"Fleet-Footed Plant Eaters: The Ornithopod Dinosaurs; Dryosaurus altus," Foster (2007) pp. 218-219"Previous work on Dryosaurus" in "Dryosaurus, a hypsolophodontid dinosaur..." Galton (1981), page 272.The remains of many individuals have been uncovered, with some sites containing hundreds of bones from Dryosaurus of multiple age groups"Fleet-Footed Plant Eaters: The Ornithopod Dinosaurs; Dryosaurus altus," Foster (2007) pg. 218A dryosaurid iguanodont. It was physically similar to Nanosaurus, although larger and with more derived teeth D. elderaeUtah, Brushy Basin member Two partial skeletons, one from a juvenile, and two additional fragmentary specimensThe second described species of DryosaurusEnigmacursorE. mollyborthwickaeColorado A partial but three-dimensionally preserved skeleton A small neornithischian LaosaurusL. altusNow known as Dryosaurus altus L. celer Wyoming Considered dubious due to fragmentary remains L. consorsNow known as Othnielosaurus consors L. gracilis Considered dubious due to fragmentary remains Nanosaurus N. agilisColorado, Brushy Basin memberA small basal neornithischian known from dozens of individuals. The holotype, YPM VP 1913, is a fragmentary skeleton from a juvenileOthnieliaO. rexColorado, Brushy Basin memberAn isolated femurConsidered dubious and many remains historically assigned to this taxon are now placed within Nanosaurus Othnielosaurus O. consors Utah and Wyoming Junior synonym of Nanosaurus Preprismatoolithus"Another Generation: The Eggs," Foster (2007) page 239. P. coloradensis Colorado, Salt Wash member Eggshells are present in great abundance at the so-called "Young Egg Locality" which seems to have been a dinosaur nesting ground. Congeneric eggshell fossils are found at additional Colorado sites including the Fruita Paleontological Area, the Uravan Locality, and Garden Park. P. coloradensis is described by John Foster as being "of the prismatic basic type", with subspherical eggs about in diameter."Eggs," Foster (2007) page 125. This oospecies has been attributed to "hypsilophodontid" dinosaurs, although a lack of associated embryo material currently makes confirming the layer's identity impossible Tichosteus T. aequifacies ColoradoTwo partial dorsal centra of a juvenile T. lucasanus ColoradoTwo partial dorsal centraUteodon U. aphanoecetesUtah, Brushy Basin memberAn articulated postcranial skeletonSometimes synonymized with Camptosaurus
Thyreophorans Ankylosaurs
Genus Species Locality Material Notes ImagesGargoyleosaurus G. parkpinorum"Jurassic Knights: The Ankylosaur Dinosaurs; Gargoyleosaurus parkpinorum," Foster (2007) pp. 216WyomingSkull and partial postcranium"Table 17.1," in Weishampel, et al. (2004). Page 364.A nodosaurid ankylosaur known from reasonably complete fossil remains. Its skull measures in length, and its total body length is an estimated . It may have weighed as much as Mymoorapelta M. maysiColorado and Utah, Brushy Basin member 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.Skull fragments, portions of three skeletons, and other postcrania"Table 17.1," in Weishampel, et al. (2004). Page 366.Both the first ankylosaur discovered in the formation and the first known North American Jurassic ankylosaur. It probably weighed in life"Jurassic Knights: The Ankylosaur Dinosaurs; Mymoorapelta maysi," Foster (2007) pp. 215-216
Stegosaurs
Genus Species Locality Material Notes ImagesAlcovasaurusA. longispinusWyoming, Brushy Basin memberGalton, Peter M. & Carpenter, Kenneth, 2016, "The plated dinosaur Stegosaurus longispinus Gilmore, 1914 (Dinosauria: Ornithischia; Upper Jurassic, western USA), type species of Alcovasaurus n. gen.", Neues Jahrbuch für Geologie und Paläontologie - Abhandlungen 279(2): 185-208A fragmentary postcranial skeleton from an adult "Table 16.1," in Weishampel, et al. (2004). Page 345.A dacentrurine stegosaurid physically similar to Stegosaurus stenops but with much larger tail spines."Roof Lizards: The Stegosaur Dinosaurs; Stegosaurus longispinus," Foster (2007) page 213. It is also similar to Kentrosaurus in having long dermal spikes on the caudal region. Possibly a species of the genus Miragaia.DeltapodusD. brodrickiStegosaur track Hesperosaurus H. mjosiWyoming and MontanaMultiple partial skeletons and skullsA stegosaurine stegosaurid that was slightly smaller than Stegosaurus itself. Hesperosaurus has a broader skull and longer, lower plates. Considered by some researchers to be a species of Stegosaurus.HypsirhophusH. discurusColorado, Brushy Basin memberA stegosaurine stegosauridMiragaiacf. M. longicollumUtah, Brushy Basin MemberAn isolated cervical plateA dacentrurine stegosauridM. sp.Wyoming and Utah, Brushy Basin MemberMultiple caudal spines, a dorsal rib and two chevronsA dacentrurine stegosaurid Stegopodus Utah Stegopodus represent only a portion of the Morrison's stegosaur tracks, which are already rare and generally only preserve the animal's hind feet Stegosaur tracks which record front feet with five digits and hind feet with three weight-bearing digits. The general morphology of the tracks fit scientific predictions made eight years in advance of the erection of Stegopodus StegosaurusS. armatusColorado, Brushy BasinSeveral caudal vertebrae and assorted fragmentary postcranial elements.S. armatus is both the first Stegosaurus species to be discovered and the original type species."Roof Lizards: The Stegosaur Dinosaurs; Stegosaurus armatus," Foster (2007) page 212. Its type specimen is poorly preserved, incomplete, and lacks diagnostic features. It has been considered dubious, with S. stenops as the neotype species for the genusS. stenopsColorado, Utah and Wyoming, Brushy Basin memberCarpenter, Kenneth. (1998). Armor of Stegosaurus stenops, and the taphonomic history of a new specimen from Garden Park, Colorado. Modern Geology, 23, 127-144.Two complete skeletons with skulls, four braincases, and at least fifty partial postcrania, all from juveniles and adultsThe best known Stegosaurus species. It has shorter limbs and larger plates than S. ungulatus"Roof Lizards: The Stegosaur Dinosaurs; Stegosaurus stenops," Foster (2007) page 213. S. sulcatusWyomingSeveral postcranial elements, including a possible shoulder spike.Often considered synonymous with S. stenops,Galton PM, Upchurch P (2004). "Stegosauria". In Weishampel DB, Dodson P, Osmólska H. The Dinosauria (2nd Edition). University of California Press. p. 361. but it may be distinct. Potentially had a shoulder spike, otherwise unknown in Stegosaurus, despite being present in most relativesGalton, P.M. (2010). "Species of plated dinosaur Stegosaurus (Morrison Formation, Late Jurassic) of western USA: new type species designation needed". Swiss Journal of Geosciences 103 (2): 187–198.