List of dinosaurs of the Morrison Formation
From Wikipedia, the free encyclopedia
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.[1] Some genera are shared between the Morrison and the Portuguese formations (Lourinhã and Alcobaça Formation), such as Torvosaurus,[2] Ceratosaurus,[3] Stegosaurus,[4] and Allosaurus.[5]
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
Color key
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Notes Uncertain or tentative taxa are in small text; |
| Genus | Species | Locality | Material | Notes | Images |
|---|---|---|---|---|---|
|
Colorado[6] |
Anomoepus from the Morrison lack the handprint impressions found associated with earlier instances of the ichnogenus in New England[6] |
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C. amplus[8] |
Now known to be based on a theropod foot[10] |
 | |||
|
C. aphanoecetes[11] |
Utah, Brushy Basin member[11] |
Reclassified as Uteodon | |||
|
C. browni[12] |
Junior synonym of C. dispar[13] | ||||
|
Twenty-five to thirty disarticulated skull elements, some with associated postcrania, and approximately ten partial, articulated skeletons, all from juveniles and adults[18] |
A member of Ankylopollexia. Junior synonyms include Camptosaurus browni, C. medius, and C. nanus | ||||
|
C. medius[12] |
Junior synonym of C. dispar[13] | ||||
|
C. nanus[12] |
Junior synonym of C. dispar[13] | ||||
|
Utah, Saltwash member[6] |
Multiple trackways have been discovered. The tracks run parallel to one another, indicating that the trackmaker was at least a somewhat social animal[6] |
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"[6] |
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|
D. nisti[19] |
"Partial skull and postcranial skeleton."[21] |
Junior synonym of Nanosaurus[22] |
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|
D. altus[14] |
Colorado and Wyoming, Brushy Basin member[16][23][9][24][25] |
The remains of many individuals have been uncovered, with some sites containing hundreds of bones from Dryosaurus of multiple age groups[23] |
A dryosaurid iguanodont. It was physically similar to Nanosaurus, although larger and with more derived teeth[24] |
 | |
|
D. elderae[22] |
Two partial skeletons, one from a juvenile, and two additional fragmentary specimens |
The second described species of Dryosaurus |
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E. mollyborthwickae |
Colorado |
A partial but three-dimensionally preserved skeleton[26] |
A small neornithischian |
 | |
|
L. altus |
Now known as Dryosaurus altus |
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|
L. celer |
Wyoming[9] |
Considered dubious due to fragmentary remains | |||
|
L. consors |
Now known as Othnielosaurus consors | ||||
|
L. gracilis |
Considered dubious due to fragmentary remains | ||||
|
N. agilis |
A small basal neornithischian known from dozens of individuals.[22] The holotype, YPM VP 1913, is a fragmentary skeleton from a juvenile[22] |
 | |||
|
O. rex[28] |
An isolated femur[28] |
Considered dubious and many remains historically assigned to this taxon are now placed within Nanosaurus |
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O. consors |
Junior synonym of Nanosaurus[22] |
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P. coloradensis[29] |
Colorado, Salt Wash member[29] |
Eggshells are present in great abundance at the so-called "Young Egg Locality" which seems to have been a dinosaur nesting ground.[29] Congeneric eggshell fossils are found at additional Colorado sites including the Fruita Paleontological Area, the Uravan Locality, and Garden Park.[29] |
P. coloradensis is described by John Foster as being "of the prismatic basic type",[29] with subspherical eggs about 10 cm (3.9 in) in diameter.[30] This oospecies has been attributed to "hypsilophodontid" dinosaurs, although a lack of associated embryo material currently makes confirming the layer's identity impossible[29] |
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|
T. aequifacies |
Colorado[16] |
Two partial dorsal centra of a juvenile |
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T. lucasanus |
Colorado[16] |
Two partial dorsal centra | |||
|
U. aphanoecetes[11] |
Utah, Brushy Basin member[11] |
An articulated postcranial skeleton |
Sometimes synonymized with Camptosaurus[22] |
 | |
Thyreophorans
Ankylosaurs
Color key
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Notes Uncertain or tentative taxa are in small text; |
| Genus | Species | Locality | Material | Notes | Images |
|---|---|---|---|---|---|
|
G. parkpinorum[31] |
Wyoming[9] |
Skull and partial postcranium[32] |
A nodosaurid ankylosaur known from reasonably complete fossil remains. Its skull measures 29 cm (11 in) in length, and its total body length is an estimated 3 to 4 m (9.8 to 13.1 ft). It may have weighed as much as 1 t (2,200 lb)[31] |
 | |
|
M. maysi[16] |
Skull fragments, portions of three skeletons, and other postcrania[34] |
Both the first ankylosaur discovered in the formation and the first known North American Jurassic ankylosaur.[35] It probably weighed 500 kg (1,100 lb) in life[35] |
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Stegosaurs
Color key
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Notes Uncertain or tentative taxa are in small text; |
| Genus | Species | Locality | Material | Notes | Images |
|---|---|---|---|---|---|
|
A. longispinus |
A fragmentary postcranial skeleton from an adult [37] |
A dacentrurine stegosaurid physically similar to Stegosaurus stenops but with much larger tail spines.[38] It is also similar to Kentrosaurus in having long dermal spikes on the caudal region. Possibly a species of the genus Miragaia.[39] |
 | ||
| Deltapodus | D. brodricki | Stegosaur track | |||
|
H. mjosi[7] |
Multiple partial skeletons and skulls[40] |
A 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. |
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|
H. discurus |
Colorado, Brushy Basin member |
A stegosaurine stegosaurid |
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|
cf. M. longicollum[39] |
Utah, Brushy Basin Member[39] |
An isolated cervical plate[39] |
A dacentrurine stegosaurid |
 | |
|
M. sp.[39] |
Wyoming and Utah, Brushy Basin Member[39] |
Multiple caudal spines, a dorsal rib and two chevrons[39] |
A dacentrurine stegosaurid |
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|
Utah[41] |
Stegopodus represent only a portion of the Morrison's stegosaur tracks, which are already rare and generally only preserve the animal's hind feet[41] |
Stegosaur tracks which record front feet with five digits and hind feet with three weight-bearing digits.[41] The general morphology of the tracks fit scientific predictions made eight years in advance of the erection of Stegopodus[41] |
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S. armatus[14] |
Several caudal vertebrae and assorted fragmentary postcranial elements.[42] |
S. armatus is both the first Stegosaurus species to be discovered and the original type species.[43] Its type specimen is poorly preserved, incomplete, and lacks diagnostic features.[42] It has been considered dubious, with S. stenops as the neotype species for the genus[42] |
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S. stenops[14] |
Colorado, Utah and Wyoming, Brushy Basin member[16][14][9][44] |
Two complete skeletons with skulls, four braincases, and at least fifty partial postcrania, all from juveniles and adults[37] |
The best known Stegosaurus species. It has shorter limbs and larger plates than S. ungulatus[45] |
 | |
|
S. sulcatus[14] |
Wyoming[46] |
Several postcranial elements, including a possible shoulder spike.[42] |
Often considered synonymous with S. stenops,[47] but it may be distinct. Potentially had a shoulder spike, otherwise unknown in Stegosaurus, despite being present in most relatives[42] |
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S. ungulatus[14] |
Several partial skeletons, including a partial braincase[42] |
S. ungulatus had longer limbs and comparatively smaller plates than the better known S. stenops.[48] Although formerly portrayed with eight tail spikes, it is now known to have had the typical four.[49] Possibly synonymous with S. stenops[50] |
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|
Indeterminate[51] |
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Other ornithischians
Color key
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Notes Uncertain or tentative taxa are in small text; |
| Genus | Species | Locality | Material | Notes | Images | |
|---|---|---|---|---|---|---|
| Anomoepus | ||||||
|
F. haagarorum[52] |
Colorado, Brushy Basin member[53] |
A partial skull and mandible with several postcranial elements[54] |
A heterodontosaurid |  |
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 Brontosaurus yahnahpin 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/Camarasaurus lewisi, 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 similar species) had appeared, including Diplodocus hallorum (formerly Seismosaurus), Supersaurus vivianae, Amphicoelias altus, and Maraapunisaurus 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.[55]
Turiasaurs
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Notes Uncertain or tentative taxa are in small text; |
| Genus | Species | Locality | Material | Notes | Images |
|---|---|---|---|---|---|
|
Turiasauria indet.[56] |
Colorado, Brushy Basin member[16] |
FHPR 18687, mold and casts of 8 teeth. |
Hypothesized to belong to a single individual, based on original teeth found associated and in a small area of a single quarry. Phylogenetic analysis suggests that FHPR 18687 teeth are the sister taxon of Losillasaurus. |
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Haplocanthosaurids
Color key
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Notes Uncertain or tentative taxa are in small text; |
| Genus | Species | Locality | Material | Notes | Images |
|---|---|---|---|---|---|
|
H. delfsi[16] |
Colorado, Brushy Basin member[16] |
Partial skeleton lacking a skull.[57] |
Small haplocanthosaurs of indeterminate classification, ranging about 14 metres (46 feet) long. |
 | |
|
H. priscus[16] |
Two skulless partial skeletons.[57] | ||||
Rebbachisaurids
Color key
|
Notes Uncertain or tentative taxa are in small text; |
| Genus | Species | Locality | Material | Notes | Images |
|---|---|---|---|---|---|
|
M. fragillimus[16] |
Colorado, Brushy Basin member[16] |
A single, now lost, dorsal neural arch.[58] |
Large rebbachisaurid. Based on a single lost neural arch 1.5 metres (4.9 feet) tall.[58] |
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Dicraeosaurids
Color key
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Notes Uncertain or tentative taxa are in small text; |
| Genus | Species | Locality | Material | Notes | Images |
|---|---|---|---|---|---|
|
A. bermani |
Utah |
A braincase and partial skull roof |
A dicraeosaurid sauropod. The material was originally assigned to Diplodocus, but redescribed as a novel genus of dicraeosaur in 2025. |  | |
|
D. polyonychius |
Wyoming[60] |
A fragmentary forelimb and partial hindlimbs. | Phylogenetic placement is uncertain.[60] | ||
|
Colorado, Brushy Basin member[16] |
"Partial skull and cervicals."[62] |
A dicraeosaurid sauropod. Originally described as "Morosaurus" agilis.[61] |
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S. emilieae |
Montana, Brushy Basin member[63] |
A partial skull and some postcrania.[55] |
A dicraeosaurid about 15m in length. |
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Diplodocids
Color key
|
Notes Uncertain or tentative taxa are in small text; |
| Genus | Species | Locality | Material | Notes | Images |
|---|---|---|---|---|---|
|
A. altus[16] |
Colorado, Brushy Basin member[16] |
2 dorsal vertebrae, femur, and a pubis.[64] |
A large diplodocoid.[65] |
 | |
|
A. ajax[16] |
—
Colorado, Brushy Basin member[16] |
A partial postcranial skeleton and posterior skull.[60] |
A robust and abundantly widespread apatosaurine diplodocid reaching lengths of up to 25 metres (82 feet).[66] "A." minimus likely belongs to a separate genus. |
 | |
|
A. louisae[14] |
Four partial specimens, one of them including a skull.[60] Three of the specimens are from DNM, one is a mid cervical from Como Bluff.[60] | ||||
|
"A." minimus |
Wyoming[9] |
"Sacrum and pelvis."[62] | |||
|
A. viator |
Howe-Stephens Quarry, Wyoming. |
Holotype specimen MAB011899, a partial skeleton containing the sacrum, ribs, a coracoid and parts of the vertebral column and hindlegs. |
A diplodocine sauropod from the younger layers of the Morrison Formation, originally considered a specimen of Diplodocus.[67] |
.png) | |
|
A. montanus |
Colorado, Brushy Basin member[28] |
A partial sacrum that cannot be distinguished from Camarasaurus or Apatosaurus.[68] |
A dubious neosauropod.[68] |
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|
B. lentus[69] |
South Dakota, Utah and Montana[69] |
2 partial postcranial skeletons, with possibly more specimens assignable.[60] |
A diplodocid about 24 metres (79 feet) in length, similar in appearance to Diplodocus. It was the rarest sauropod in the Morrison Formation.[70] |
 | |
| B. sp. | Colorado, Wyoming, Utah and Oklahoma[69] | ||||
|
B. excelsus |
Two postcranial skeletons.[60] |
Previously considered a species of Apatosaurus as per Riggs (1903). |
 | ||
|
B. parvus |
Utah and Wyoming, Salt Wash and Brushy Basin members |
Three headless skeletons.[60] |
Originally called Elosaurus. |
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B. yahnahpin[60] |
Wyoming, Brushy Basin member |
A partial postcranial skeleton.[60] |
An apatosaurine diplodocid slightly more primitive than Apatosaurus. Formerly placed in separate genus Eobrontosaurus. |
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D. carnegii[14] |
Known from two skulls, five partial skeletons that lack skulls and manus, and hundreds of isolated postcranial remains.[73] |
A large diplodocid reaching lengths of up to 28 metres (92 feet). It was one of the most abundant sauropods in the area.[74] |
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D. hallorum |
New Mexico, Wyoming and Utah, Brushy Basin and Salt Wash members[51] |
At least 4 partial postcranial skeletons[60] |
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D. lacustris[16] |
Colorado, Brushy Basin member[16] |
Known from teeth and skull remains, the latter now referred to Camarasaurus.[60] Teeth cannot be referred beyond Flagellicaudata.[60] |
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D. longus[14] |
Colorado, Brushy Basin member[16] |
Several caudal vertebrae.[79] |
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G. hayi |
Known from a partial skeleton and braincase.[73] |
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|
G. pabsti |
Colorado and Wyoming, Brushy Basin member |
A skull and partial postcranial skeleton, another individual known from partial skull.[60] |
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K. siberi |
Wyoming, Salt Wash member[80] |
Skull and cervical vertebrae.[80] |
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|
S. maximus[17] |
Several partial postcranial skeletons.[83] |
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.[83] |
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S. vivianae[16] |
Colorado and Wyoming, Brushy Basin member |
Known from several partial postcranial skeletons.[64] |
A large diplodocid about 33–34 m (108–112 ft) in length |
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Macronarians
Color key
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Notes Uncertain or tentative taxa are in small text; |
| Genus | Species | Locality | Material | Notes | Images |
|---|---|---|---|---|---|
|
B. altithorax[7] |
Colorado, Brushy Basin and Salt Wash members[16] |
Several partial skeletons and a partial skull. |
A large brachiosaurid about 18–22 m (59–72 ft) long. |
 | |
|
C. annae[14] |
Utah, Brushy Basin member[14] |
A dorsal vertebra. |
Camarasaurs reached an adult size of about 18 metres (59 feet) in length.[84] 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. |
 | |
|
C. grandis[16] |
"At least 6 partial skeletons including 2 skulls, hundreds of postcranial elements."[57] | ||||
|
C. lentus[14] |
"5 skeletons with skulls, hundreds of postcranial elements"[57] | ||||
|
Colorado, Brushy Basin member[16] |
A nearly complete postcranial skeleton.[57] | ||||
|
C. supremus[16] |
At least 4 partial skeletons including partial skulls. Many possible postcranial remains from Oklahoma.[86] | ||||
|
Indeterminate. |
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| Dystrophaeus | D. viaemalae[89] |
Utah, Tidwell member[89] |
Multiple vertebrae, teeth and incomplete forelimb material.[89] | Previously recovered as a diplodocid, now recovered as a macronarian[89] Type material fragmentary, but recent rediscovery of type locality has discovered more material.[90] | |
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, and the megalosaur Torvosaurus tanneri (including Edmarka rex). Allosaurids included the common Allosaurus fragilis (including Epanterias amplexus), A. jimmadseni and A. anax (previously referred to Saurophaganax maximus).
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.[91]
Allosauroidea
Color key
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Notes Uncertain or tentative taxa are in small text; |
| Genus | Species | Locality | Material | Notes | Images |
|---|---|---|---|---|---|
|
A. fragilis[14] |
Colorado, New Mexico, Oklahoma, South Dakota, Utah and Wyoming, Brushy Basin member[16][51][17][87][9][92] |
"At least [three] complete skulls, many partial skulls and skull elements, many partial and complete skeletons representing at least 60 individuals."[93] It was the most common large carnivore in the area.[94][95][96] |
 | ||
|
A. jimmadseni[97] |
Wyoming and Utah, Brushy Basin and Salt Wash members[92][96] |
At least 15 specimens, including several skulls. | |||
|
A. anax[83] |
Oklahoma, Kenton Member[83] | Postorbital and partial postcranial material |  | ||
|
A. valens |
Colorado[82] |
Half of a proximal caudal centrum | |||
|
C. atrox |
Wyoming, Brushy Basin member[99] |
A fragmentary skull and assorted postcrania.[99] |
Considered a junior synonym of Allosaurus. |
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E. amplexus |
Colorado, Brushy Basin member[100] |
Several fragmentary postcranial elements of 2 individuals,[101] possible additional remains known from Wyoming.[102] | |||
|
L. lucaris |
Wyoming, Brushy Basin member[82] |
A fragmentary skull and several postcranial elements.[98][82] |
Junior synonym of A. fragilis.[82] |
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|
L. ferox |
Wyoming, Brushy Basin member[82] |
A partial skull, dentaries, and fragmentary postcrania.[103][82] |
Known from one specimen with several pathologies. Today considered a junior synonym of A. fragilis.[82] | ||
Ceratosaurs
Color key
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Notes Uncertain or tentative taxa are in small text; |
| Genus | Species | Locality | Material | Notes | Images |
|---|---|---|---|---|---|
|
C. dentisulcatus[14] |
Utah[14] |
"Partial skull, vertebrae, [and] limb elements."[104] |
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. |
 | |
|
C. magnicornis[16] |
Colorado[16] |
"Skull [and] assorted postcrania."[104] | |||
|
C. nasicornis[16] |
Remains of "5 individuals, including [a] nearly complete adult skeleton and subadult skeleton."[104] | ||||
|
Indeterminate.[9] |
Wyoming[9] |
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|
Indeterminate.[16] |
Colorado[16] |
Previously referred to Elaphrosaurus,[105][106][107] these remains are probably not referable to that genus and are best considered indeterminate beyond Ceratosauria.[108] |
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Intermediate[16] |
Colorado[16] |
Now thought to be indeterminate beyond Ceratosauria. |
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|
F. churei[109] |
Wyoming[109] |
Tibia, astragalus, fibula.[109] |
A fragmentary theropod which may be a ceratosaurid. |
 | |
Coelurosaurs
Coelurosaurs, the group of theropods most closely related to and including birds, included Coelurus fragilis, Ornitholestes hermanni, Tanycolagreus topwilsoni, the possible troodontid Koparion douglassi, the definite troodontid Hesperornithoides, and the early tyrannosauroid Stokesosaurus clevelandi.
Color key
|
Notes Uncertain or tentative taxa are in small text; |
| Genus | Species | Locality | Material | Notes | Images |
|---|---|---|---|---|---|
| Alvarezsauroidea indet.[110] | Indeterminate | Wyoming | Two cervical vertebrae and an astragalus | An early alvarezsauroid filling a gap in the clade's fossil record. The material was originally classified as part of the Coelurus fragilis hypodigm. | |
|
C. fragilis[14] |
A partial skeleton in several syntypes and several fragmentary referred specimens.[111] |
A basal coelurosaurian about 2.3 metres (7.5 feet) long. |
 | ||
|
Indeterminate[16] |
Colorado[16] |
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|
H. miessleri |
Wyoming |
An early troodontid. |
 | ||
|
K. douglassi[14] |
Utah[14] |
A small theropod thought to be one of the oldest known troodontids. |
 | ||
|
P. thomsoni[16] |
Colorado, Brushy Basin member[16] |
A distal radius | |||
|
O. hermanni[9] |
Wyoming[9] |
"Skull and associated postcranial skeleton."[111] |
A small basal coelurosaurian about 2 metres (6.6 feet) long. |
 | |
|
S. clevelandi[14] |
Utah[14] |
"Illium, associated elements and pelvic cranial material. [sic]"[113] |
A possible early tyrannosauroid about 4 metres (13 feet) in length. |
 | |
|
T. topwilsoni |
Wyoming and Utah |
A basal coelurosaurian about 3.4 metres (11 feet) long, similar in appearance to Coelurus. |
 | ||
Megalosauroids
Color key
|
Notes Uncertain or tentative taxa are in small text; |
| Genus | Species | Locality | Material | Notes | Images |
|---|---|---|---|---|---|
|
E. rex[9] |
|
Possibly a junior synonym of Torvosaurus tanneri. | |||
|
M. bicentesimus[14] |
Partial skeleton, including part of a skull.[114] |
A medium-sized piatnitzkysaurid megalosauroid about 6 metres (20 feet) in length. |
 | ||
|
T. tanneri[14] |
"Partial skeletons of at least [three] individuals."[115] |
A large, robust megalosaurid reaching lengths of up to 9 m (30 ft).[116] One of the largest carnivores of the formation. |
 | ||
Eggs
_1.jpg)
Dinosaur eggs have been found in Utah.[14]
Tracks
Ornithopods
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.[41] 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.[41] 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.[41] 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.[41] Since the erection of Stegopodus, more trackways have been found, however none have preserved traces of the front feet, and stegosaur traces remain rare.[41]
Theropods
Indeterminate theropod tracks have been recovered from both Utah and Arizona.[91]