The Morrison Formation is a distinctive sequence of Upper Jurassic sedimentary rock 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.
It is centered in Wyoming and Colorado, with outcrops in Montana, North Dakota, South Dakota, Nebraska, Kansas, the panhandles of Oklahoma and Texas, New Mexico, Arizona, Utah, and Idaho. Equivalent rocks under different names are found in Canada. It covers an area of 1.5 million square kilometers (600,000 square miles), although only a tiny fraction is exposed and accessible to geologists and paleontologists. Over 75% is still buried under the prairie to the east, and much of its western paleogeographic extent was eroded during exhumation of the Rocky Mountains.
It was named after Morrison, Colorado, where the first fossils in the formation were discovered by Arthur Lakes in 1877. That same year, it became the center of the Bone Wars, a fossil-collecting rivalry between early paleontologists Othniel Charles Marsh and Edward Drinker Cope. In Colorado, New Mexico, and Utah, the Morrison Formation was a major source of uranium ore.
Stratigraphic range: Late Jurassic, 156.3–146.8 Ma
The distinctive banding of the Morrison Formation, a group of rock layers that occur throughout Dinosaur National Monument and the source of fossils like those found at the Dinosaur Quarry
|Underlies||Cedar Mountain Formation, Cloverly Formation, Lakota Formation|
|Overlies||Summerville Formation, Curtis Formation, Bell Ranch Formation|
|Thickness||Up to 200 m|
|Other||Sandstone, siltstone, limestone|
|Region||Central North America|
|Named for||Morrison, Colorado|
According to radiometric dating, the Morrison Formation dates from 156.3 ± 2 million years old (Ma) at its base, to 146.8 ± 1 million years old at the top, which places it in the earliest Kimmeridgian, and early Tithonian stages of the late Jurassic. This is similar in age to the Solnhofen Limestone Formation in Germany and the Tendaguru Formation in Tanzania. The age and much of the fauna is similar to the Lourinhã Formation in Portugal. Throughout the western United States, it variously overlies the Middle Jurassic Summerville, Sundance, Bell Ranch, Wanakah, and Stump Formations.
At the time, the supercontinent of Laurasia had recently split into the continents of North America and Eurasia, although they were still connected by land bridges. North America moved north and was passing through the subtropical regions.
The Morrison Basin, which stretched from New Mexico in the south to Alberta and Saskatchewan in the north, was formed during the Nevadan orogeny, a precursor event to later orogenic episodes that created the Rocky Mountains started pushing up to the west. The deposits from their east-facing drainage basins, carried by streams and rivers from the Elko Highlands (along the borders of present-day Nevada and Utah) and deposited in swampy lowlands, lakes, river channels and floodplains, became the Morrison Formation.
In the north, the Sundance Sea, an extension of the Arctic Ocean, stretched through Canada down to the United States. Coal is found in the Morrison Formation of Montana, which means that the northern part of the formation, along the shores of the sea, was wet and swampy, with more vegetation. Aeolian, or wind-deposited sandstones, are found in the southwestern part, which indicates it was much more arid—a desert, with sand dunes.
In the Colorado Plateau region, the Morrison Formation is further broken into four sub-divisions, or members. From the oldest to the most recent, they are:
Deposition in the Morrison Formation ended about 147 Ma. The latest Morrison strata are followed by a thirty-million-year gap in the geologic record. The overlying units are the Lower Cretaceous Cedar Mountain, Burro Canyon, Lytle, and Cloverly Formations.
Though many of the Morrison Formation fossils are fragmentary, they are sufficient to provide a good picture of the flora and fauna in the Morrison Basin during the Kimmeridgian. Overall, the climate was dry, similar to a savanna but, since there were no angiosperms (grasses, flowers, and some trees), the flora was quite different. Conifers, the dominant plants of the time, were to be found with ginkgos, cycads, tree ferns, and horsetail rushes. Much of the fossilized vegetation was riparian, living along the river flood plains. Insects were very similar to modern species, with termites building 30-meter-tall (98 ft) nests. Along the rivers, there were fish, frogs, salamanders, lizards, crocodiles, turtles, pterosaurs, crayfish, clams, and mammaliforms.
The dinosaurs were most likely riparian, as well. Hundreds of dinosaur fossils have been discovered, such as Allosaurus, Camptosaurus, Ornitholestes, several stegosaurs comprising at least two species of Stegosaurus and the slightly older Hesperosaurus, and the early ankylosaurs, Mymoorapelta and Gargoyleosaurus, most notably a very broad range of sauropods (the giants of the Mesozoic era). Since at least some of these species are known to have nested in the area (Camptosaurus embryoes have been discovered), there are indications that it was a good environment for dinosaurs and not just home to migratory, seasonal populations.
Sauropods that have been discovered include Diplodocus (most famously, the first nearly complete specimen of D. carnegii, which is now exhibited at the Carnegie Museum of Natural History, in Pittsburgh, Pennsylvania), Camarasaurus (the most commonly found sauropod), Brachiosaurus, Apatosaurus, Brontosaurus, Barosaurus, the uncommon Haplocanthosaurus and Supersaurus. The very diversity of the sauropods has raised some questions about how they could all co-exist. While their body shapes are very similar (long neck, long tail, huge elephant-like body), they are assumed to have had very different feeding strategies, in order for all to have existed in the same time frame and similar environment.
Locations where significant Morrison Formation fossil discoveries have been made include:
Allosaurus () is a genus of carnivorous theropod dinosaur that lived 155 to 145 million years ago during the late Jurassic period (Kimmeridgian to late Tithonian). The name "Allosaurus" means "different lizard" alluding to its unique concave vertebrae (at the time of its discovery). It is derived from the Greek ἄλλος/allos ("different, other") and σαῦρος/sauros ("lizard / generic reptile"). The first fossil remains that could definitively be ascribed to this genus were described in 1877 by paleontologist Othniel Charles Marsh. As one of the first well-known theropod dinosaurs, it has long attracted attention outside of paleontological circles. Indeed, it has been a top feature in several films and documentaries about prehistoric life.
Allosaurus was a large bipedal predator. Its skull was large and equipped with dozens of sharp, serrated teeth. It averaged 9.5 metres (31 ft) in length, though fragmentary remains suggest it could have reached over 12 m (39 ft). Relative to the large and powerful hindlimbs, its three-fingered forelimbs were small, and the body was balanced by a long and heavily muscled tail. It is classified as an allosaurid, a type of carnosaurian theropod dinosaur. The genus has a complicated taxonomy, and includes an uncertain number of valid species, the best known of which is A. fragilis. The bulk of Allosaurus remains have come from North America's Morrison Formation, with material also known from Portugal and possibly Tanzania. It was known for over half of the 20th century as Antrodemus, but a study of the copious remains from the Cleveland-Lloyd Dinosaur Quarry brought the name "Allosaurus" back to prominence and established it as one of the best-known dinosaurs.
As the most abundant large predator in the Morrison Formation, Allosaurus was at the top of the food chain, probably preying on contemporaneous large herbivorous dinosaurs, and perhaps even other predators. Potential prey included ornithopods, stegosaurids, and sauropods. Some paleontologists interpret Allosaurus as having had cooperative social behavior, and hunting in packs, while others believe individuals may have been aggressive toward each other, and that congregations of this genus are the result of lone individuals feeding on the same carcasses.Amphicoelias
Amphicoelias (, meaning "biconcave", from the Greek ἀμφί, amphi: "on both sides", and κοῖλος, koilos: "hollow, concave") is a genus of herbivorous sauropod dinosaur that lived approximately 150 million years ago during the Tithonian (Late Jurassic Period) of what is now Colorado, United States. A herbivore, Amphicoelias was moderately sized at about 25 m (82 ft) long–roughly the same length as Diplodocus, to which it was related. Its hindlimbs were very long and thin, and its forelimbs were proportionally longer than in relatives.
The namesake fossil of the type species Amphicoelias altus, American Museum of Natural History 5764, is uncertain in included material. When described by Edward Drinker Cope shortly after its discovery in 1877, Amphicoelias was noted to include many back vertebrae, a single pubis, and a femur. However, after purchase and cataloging of the material by the AMNH, Henry Fairfield Osborn and Charles Mook described that the specimen had only two vertebrae, a pubis, femur, tooth, scapula, coracoid, ulna and a second femur. The additional material, not mentioned by Cope, was found close in proximity to the holotype and was similar to Diplodocus, a relative of Amphicoelias. Their assignment was questioned by subsequent authors Emanuel Tschopp et al. in an analysis of Diplodocidae.
During the description of Amphicoelias altus in 1877, Cope additionally named A. latus, for a femur and tail vertebrae. Following its description, Osborn and Mook in 1921 reidentified the material as a specimen of Camarasaurus, an assignment followed by other authors who reviewed the material. A year later 1878, Cope named the third species of Amphicoelias, A. fragillimus for a gigantic dorsal vertebra that was subsequently lost. Measuring approximately 2.7 m (8.9 ft) if reconstructed based on Diplodocus, early estimates for the length of the animal in life were between 40 and 60 m (130 and 200 ft) long. Due to the incomplete nature, such lengths–the longest of any known dinosaur and sauropod–were largely ignored. In 2018, Kenneth Carpenter renamed Amphicoelias fragillimus as the new genus Maraapunisaurus, and reclassified it from Diplodocidae to Rebbachisauridae.Atlantosaurus
Atlantosaurus (meaning "Atlas lizard") is a dubious genus of sauropod dinosaur. It contains a single species, Atlantosaurus montanus, from the upper Morrison Formation of Colorado, United States. Atlantosaurus was the first sauropod to be described during the infamous 19th century Bone Wars, during which scientific methodology suffered in favor of pursuit of academic acclaim.Barosaurus
Barosaurus ( BARR-o-SAWR-əs) was a giant, long-tailed, long-necked, plant-eating dinosaur closely related to the more familiar Diplodocus. Remains have been found in the Morrison Formation from the Upper Jurassic Period of Utah and South Dakota (and possibly Africa, as exemplified by the Kadsi Formation). It is present in stratigraphic zones 2-5.The composite term Barosaurus comes from the Greek words barys (βαρυς) meaning "heavy" and sauros (σαυρος) meaning "lizard"; thus "heavy lizard".Brontosaurus
Brontosaurus (; meaning "thunder lizard" from Greek βροντή, brontē "thunder" and σαῦρος, sauros "lizard") is a genus of gigantic quadruped sauropod dinosaurs. Although the type species, B. excelsus, had long been considered a species of the closely related Apatosaurus, researchers proposed in 2015 that Brontosaurus is a genus separate from Apatosaurus and that it contains three species: B. excelsus, B. yahnahpin, and B. parvus.Brontosaurus had a long, thin neck and a small head adapted for a herbivorous lifestyle; a bulky, heavy torso; and a long, whip-like tail. The various species lived during the Late Jurassic epoch in the Morrison Formation of what is now North America, and were extinct by the end of the Jurassic. Adult individuals of Brontosaurus are estimated to have weighed up to 15 tonnes (15 long tons; 17 short tons) and measured up to 22 metres (72 ft) long.
As the archetypal sauropod, Brontosaurus is one of the best-known dinosaurs and has been featured in film, advertising, and postage stamps, as well as many other types of media.Camarasaurus
Camarasaurus ( KAM-ər-ə-SAWR-əs) was a genus of quadrupedal, herbivorous dinosaurs. It was the most common of the giant sauropods to be found in North America. Its fossil remains have been found in the Morrison Formation of Colorado and Utah, dating to the Late Jurassic epoch (Kimmeridgian to Tithonian stages), between 155 and 145 million years ago.
Camarasaurus presented a distinctive cranial profile of a blunt snout and an arched skull that was remarkably square. It likely travelled in herds, or at least in family groups.
The name means "chambered lizard", referring to the hollow chambers in its vertebrae (Greek καμαρα/kamara meaning "vaulted chamber", or anything with an arched cover, and σαυρος/sauros meaning "lizard").Diplodocus
Diplodocus (, , or ) is a genus of diplodocid sauropod dinosaurs whose fossils were first discovered in 1877 by S. W. Williston. The generic name, coined by Othniel Charles Marsh in 1878, is a neo-Latin term derived from Greek διπλός (diplos) "double" and δοκός (dokos) "beam", in reference to the double-beamed chevron bones located in the underside of the tail, which were then considered unique. It is now common scientific opinion that Seismosaurus hallorum is a species of Diplodocus.
This genus of dinosaurs lived in what is now mid-western North America at the end of the Jurassic period. Diplodocus is one of the more common dinosaur fossils found in the middle to upper Morrison Formation, between about 154 and 152 million years ago, during the late Kimmeridgian age. The Morrison Formation records an environment and time dominated by gigantic sauropod dinosaurs, such as Apatosaurus, Barosaurus, Brachiosaurus, Brontosaurus, and Camarasaurus. Its great size may have been a deterrent to the predators Allosaurus and Ceratosaurus: their remains have been found in the same strata, which suggests that they coexisted with Diplodocus.
Diplodocus is among the most easily identifiable dinosaurs, with its typical sauropod shape, long neck and tail, and four sturdy legs. For many years, it was the longest dinosaur known.Dryosaurus
Dryosaurus ( DRY-o-SAWR-əs; meaning 'tree lizard', Greek δρυς/drys meaning 'tree, oak' and σαυρος/sauros meaning 'lizard'; the name reflects the forested habitat, not a vague oak-leaf shape of its cheek teeth as is sometimes assumed) is a genus of an ornithopod dinosaur that lived in the Late Jurassic period. It was an iguanodont (formerly classified as a hypsilophodont). Fossils have been found in the western United States (and supposedly the Marnes de Bleville locality in Europe), and were first discovered in the late 19th century. Valdosaurus canaliculatus and Dysalotosaurus lettowvorbecki were both formerly considered to represent species of Dryosaurus.Fruitadens
Fruitadens is a genus of heterodontosaurid dinosaur. The name means "Fruita tooth", in reference to Fruita, Colorado (USA), where its fossils were first found. It is known from partial skulls and skeletons from at least four individuals of differing biological ages, found in Tithonian (Late Jurassic) rocks of the Morrison Formation in Colorado. Fruitadens is the smallest known ornithischian dinosaur, with young adults estimated at 65 to 75 cm (26 to 30 in) in length and 0.5 to 0.75 kg (1.1 to 1.7 lb) in weight. It is interpreted as an omnivore and represents one of the latest-surviving heterodontosaurids.Garden Park, Colorado
Garden Park is a paleontological site in Fremont County, Colorado, known for its Jurassic dinosaurs and the role the specimens played in the infamous Bone Wars of the late 19th century. Located 10 km (6.2 mi) north of Cañon City, the name originates from the area providing vegetables to the miners at nearby Cripple Creek in the 19th century. Garden Park proper is a triangular valley surrounded by cliffs on the southeast and southwest and by mountains to the north; however, the name is also refers to the dinosaur sites on top and along the cliffs. The dinosaur sites now form the Garden Park Paleontological Resource Area, which is overseen by the Bureau of Land Management.Gargoyleosaurus
Gargoyleosaurus (meaning "gargoyle lizard") is one of the earliest ankylosaurs known from reasonably complete fossil remains. Its skull measures 29 centimetres (11 in) in length, and its total body length is an estimated 3 to 4 metres (9.8 to 13.1 ft). It may have weighed as much as 1 tonne (2,200 lb). The holotype was discovered at the Bone Cabin Quarry West locality, in Albany County, Wyoming in exposures of the Upper Jurassic (Kimmeridgian to Tithonian stages) Morrison Formation.The type species, G. parkpinorum (originally G. parkpini) was described by Ken Carpenter et al. in 1998. A mounted skeletal reconstruction of Gargoyleosaurus parkpinorum can be seen at the Denver Museum of Nature and Science. Gargoyleosaurus was present in stratigraphic zone 2 of the Morrison Formation.Kaatedocus
Kaatedocus is a genus of diplodocine flagellicaudatan sauropod known from the middle Late Jurassic (Kimmeridgian stage) of northern Wyoming, United States. It is known from well-preserved skull and cervical vertebrae which were collected in the lower part of the Morrison Formation. The type and only species is Kaatedocus siberi, described in 2012 by Emanuel Tschopp and Octávio Mateus.Mymoorapelta
Mymoorapelta ("Shield of Mygatt-Moore") is an ankylosaur from the Late Jurassic (Kimmeridgian-Tithonian) Morrison Formation (Brushy Basin Member) of western Colorado, USA. The taxon is known from portions of a disarticulated skull, parts of three different skeletons and other postcranial remains. It is present in stratigraphic zones 4 and 5 of the Morrison Formation.Othnielosaurus
Othnielosaurus is a genus of ornithischian dinosaur that lived about 155 to 148 million years ago, during the Late Jurassic-age Morrison Formation of the western United States. It is named in honor of famed paleontologist Othniel Charles Marsh, and was formerly assigned to the genus Laosaurus. This genus was coined to hold fossils formerly included in Othnielia, which is based on remains that may be too sparse to hold a name. O.C. Marsh named several species and genera in the late 19th century that have come to be recognized as hypsilophodonts or hypsilophodont-like animals, including Nanosaurus agilis, "N." rex (Othnielia), Laosaurus celer, L. consors, and L. gracilis. This taxonomy has become very complicated, with numerous attempts at revision in the years since; Othnielosaurus is part of decades of research to untangle the taxonomy left behind by Marsh and his rival Edward Drinker Cope from the Bone Wars. Othnielosaurus has usually been classified as a hypsilophodont, a type of generalized small bipedal herbivore or omnivore, although recent research has called this and the existence of a distinct group of hypsilophodonts into question.Stegosaurus
Stegosaurus (), from Greek stegos (στέγος) which means roof and sauros (σαῦρος) which means lizard (Greek: Στεγόσαυρος), is a genus of herbivorous thyreophoran dinosaur. Fossils of this genus date to the Late Jurassic period, where they are found in Kimmeridgian to early Tithonian aged strata, between 155 and 150 million years ago, in the western United States and Portugal. Of the species that have been classified in the upper Morrison Formation of the western US, only three are universally recognized; S. stenops, S. ungulatus and S. sulcatus. The remains of over 80 individual animals of this genus have been found. Stegosaurus would have lived alongside dinosaurs such as Apatosaurus, Diplodocus, Brachiosaurus, Allosaurus, and Ceratosaurus; the latter two may have been predators of it.
These were large, heavily built, herbivorous quadrupeds with rounded backs, short fore limbs, long hind limbs, and tails held high in the air. Due to their distinctive combination of broad, upright plates and tail tipped with spikes, Stegosaurus is one of the most recognizable kinds of dinosaurs. The function of this array of plates and spikes has been the subject of much speculation among scientists. Today, it is generally agreed that their spiked tails were most likely used for defense against predators, while their plates may have been used primarily for display, and secondarily for thermoregulatory functions. Stegosaurus had a relatively low brain-to-body mass ratio. It had a short neck and a small head, meaning it most likely ate low-lying bushes and shrubs. One species, Stegosaurus ungulatus, is the largest known of all the stegosaurians (bigger than related dinosaurs such as Kentrosaurus and Huayangosaurus).
Stegosaurus remains were first identified during the "Bone Wars" by Othniel Charles Marsh. The first known skeletons were fragmentary and the bones were scattered, and it would be many years before the true appearance of these animals, including their posture and plate arrangement, became well understood. Despite its popularity in books and film, mounted skeletons of Stegosaurus did not become a staple of major natural history museums until the mid-20th century, and many museums have had to assemble composite displays from several different specimens due to a lack of complete skeletons. Stegosaurus is one of the best-known dinosaurs, and has been featured in film, postal stamps, and many other types of media.Supersaurus
Supersaurus (meaning "super lizard") is a genus of diplodocid sauropod dinosaur that lived in North America during the Late Jurassic period. The type species, S. vivianae, was first discovered by Vivian Jones of Delta, Colorado, in the middle Morrison Formation of Colorado in 1972. The fossil remains came from the Brushy Basin Member of the formation, dating to about 153 million years ago. A potential second species, S. lourinhanensis, is known from Portugal and has been dated to a similar time.Suuwassea
Suuwassea (meaning "ancient thunder") is a genus of dicraeosaurid sauropod dinosaur found in the Upper Jurassic strata of the Morrison Formation, located in southern Carbon County, Montana, United States. The fossil remains were recovered in a series of expeditions during a period spanning the years 1999 and 2000, described by J.D. Harris and Peter Dodson in 2004. They consist of a disarticulated but associated partial skeleton, including partial vertebral series and limb bones.Tithonian
In the geological timescale, the Tithonian is the latest age of the Late Jurassic epoch or the uppermost stage of the Upper Jurassic series. It spans the time between 152.1 ± 4 Ma and 145.0 ± 4 Ma (million years ago). It is preceded by the Kimmeridgian and followed by the Berriasian stage (part of the Cretaceous).Uteodon
Uteodon is a genus of herbivorous iguanodontian dinosaur. It is a basal iguanodontian which lived during the late Jurassic period in what is now Uintah County, Utah. It is known from the middle of the Brushy Basin Member, Morrison Formation. This genus was named by Andrew T. McDonald in 2011 and the type species is Uteodon aphanoecetes. U. aphanoecetes was previously referred to as Camptosaurus aphanoecetes, and was first described in 2008 by Carpenter and Wilson.