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Cedar Mountain Formation

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The Cedar Mountain Formation is the name given to a distinctive sedimentary geologic formation in eastern Utah , spanning most of the early and mid- Cretaceous . The formation was named for Cedar Mountain in northern Emery County, Utah , where William Lee Stokes first studied the exposures in 1944.

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46-696: The formation occurs between the underlying Morrison Formation and overlying Naturita Formation (sometimes formerly called the Dakota Formation ). It is composed of non-marine sediments, that is, sediments deposited in rivers, lakes and on flood plains. Based on various fossils and radiometric dates , the Cedar Mountain Formation was deposited during the last half of the Early Cretaceous Epoch, about 127 - 98 million years ago (mya). It has lithography similar to

92-531: A middle dinosaur assemblage between the older and younger ones is controversial because the evidence mostly depends on a single specimen of the ornithopod Tenontosaurus from high in the Ruby Ranch Member and the sauropod Astrodon from low in the Ruby Ranch. Regardless, the upper and lower dinosaur assemblages in the Cedar Mountain Formation document the separation of North America and Europe,

138-465: 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 some of the first fossils in the formation were discovered by Arthur Lakes in 1877. That same year, it became

184-416: A year earlier ) as one of his three families of dinosaurs (alongside Megalosauridae and Scelidosauridae ), including within it the genera Iguanodon , Hypsilophodon , and Hadrosaurus , in addition to Cetiosaurus and tentatively Stenopelix . The term Ornithopoda was erected by Othniel Charles Marsh in 1881 as part of his then still ongoing investigation of the classification of Dinosauria. It

230-513: Is a clade of ornithischian dinosaurs , called ornithopods ( / ˈ ɔːr n ə θ ə ˌ p ɒ d z , ɔːr ˈ n ɪ θ -/ ). They represent one of the most successful groups of herbivorous dinosaurs during the Cretaceous . The most primitive members of the group were bipedal and relatively small-sized, while advanced members of the subgroup Iguanodontia became quadrupedal and developed large body size. Their major evolutionary advantage

276-618: Is a debate as to whether there are five members or four depending whether the Buckhorn Conglomerate is considered to be at the top of the Morrison Formation or at the base of the Cedar Mountain Formation; most geologists and paleontologists consider it part of the Cedar Mountain Formation. In ascending order the remaining members are the Yellow Cat Member, Poison Strip Sandstone, Ruby Ranch Member, and

322-768: 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

368-606: Is marked by an unconformity of variable length, and typically signifies 10-49 million years of missing geologic time. This boundary between the Morrison and Cedar Mountain is commonly marked by a horizon of carbonate nodules or by highly polished pebbles that are allegedly gastroliths. Although not part of the Cedar Mountain Formation, the Naturita Formation immediately overlies the Cedar Mountain and marks

414-494: Is often listed as an infraorder within a suborder Ornithopoda, though Benton (2004) lists Ornithopoda as an infraorder and does not rank Iguanodontia. Traditionally, iguanodontians were grouped into the superfamily Iguanodontoidea and family Iguanodontidae . However, phylogenetic studies show that the traditional "iguanodontids" are a paraphyletic grade leading up to the hadrosaurs (duck-billed dinosaurs). Groups like Iguanodontoidea are sometimes still used as unranked clades in

460-512: Is usually given the rank of Suborder, within the order Ornithischia. While ranked taxonomy has largely fallen out of favour among dinosaur paleontologists, some researchers have continued to employ such a classification, though sources have differed on what its rank should be. Benton (2004) placed it as an infraorder within the suborder Cerapoda (originally named as an unranked clade ), while others, such as Ibiricu et al. 2010, have retained it at its traditional ranking of suborder. Iguanodontia

506-475: The Burro Canyon Formation in the region. Dinosaur fossils occur throughout the formation, but their study has only occurred since the early 1990s. The dinosaurs in the lower part of the formation differ from those in the upper part. These two dinosaur assemblages, characterized by distinct dinosaurs, show the replacement of older, European-like dinosaurs with younger, Asian-like dinosaurs as

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552-511: The Greek ornithos , ornis ("bird") and pous , podos ("feet"); this is in reference to members’ characteristic birdlike feet. They were also characterized as lacking in body armour, not developing a horny beak , having an elongated pubis (that eventually extended past the ilium ), and having a missing hole in the lower jaw (a Mandibular fenestra ). A variety of ornithopods, and related ornithischians , had thin cartilaginous plates along

598-831: The Hypsilophodontidae is problematic. The group previously consisted of all non- iguanodontian bipedal ornithischians, but a phylogenetic reappraisal has shown such species to be paraphyletic . As such, the hypsilophodont family is currently represented only by Hypsilophodon . Later ornithopods became larger, but never rivalled the incredible size of the long-necked, long-tailed sauropods that they partially supplanted. The very largest, such as Shantungosaurus , were as heavy as medium-sized sauropods (up to 23 metric tons /25 short tons ), but never grew much beyond 15 metres (50 feet). Historically, most indeterminate ornithischian bipeds were lumped in as ornithopods. Most have since been reclassified. Ornithopoda

644-506: The theropods , to help them balance as they ran on their hind legs. Later ornithopods became more adapted to grazing on all fours; their spines curved, and came to resemble the spines of modern ground-feeders, such as the bison . As they became more adapted to eating while bent over, they became facultative quadrupeds; still running on two legs, and comfortable reaching up into trees, but spending most of their time walking or grazing on all fours. The taxonomy of dinosaurs previously ascribed to

690-610: The Bullington Member, which has been discarded entirely. 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 ,

736-645: The European Hypsilophodon and three American taxa he named himself, Camptonotus , Laosaurus , and Nanosaurus . Camptonotus was in 1885 renamed to Camptosaurus , as the original name was pre-occupied by a cricket ; the associated family followed suit, becoming Camptosauridae. In Iguanodontidae, only found in Europe, he included Iguanodon and Vectisaurus . In Hadrosauridae, he included Hadrosaurus , Cionodon , and tentatively Agathaumas . Ornithopoda means "bird feet", from

782-696: The Jackpile uranium body discovered near Grants, New Mexico in 1951. The ore deposits in the rich Grants mineral belt are concentrated in sandstone beds of the Westwater Canyon Member and the Jackpile Member. Mines in this belt produced 340,000,000 pounds (150,000,000 kg) of U 3 O 8 between 1948 and 2002. The uranium was precipitated by plant debris and humate that acted as reducing agents. Iguanodontia Ornithopoda ( / ˌ ɔːr n ə ˈ θ ɒ p ə d ə / )

828-649: The Lower Yellow Cat and Ruby Ranch Members. Indeterminate dromaeosaurine present in the Mussentuchit Member. Indeterminate deinonychosaurian remains present in the Mussentuchit member. Indeterminate velociraptorine remains present in the Mussentuchit Member. Indeterminate troodontid remains present in the Mussentuchit Member. Indeterminate therizinosaurid remains present in the Mussentuchit Member. Indeterminate dromaeosaurine remains present in

874-466: The Mussentuchit Member. Each of these members are named after a geographic area where they were first studied. The Cedar Mountain Formation is proving to contain one of the world's richest and most diverse Early Cretaceous dinosaur faunas. The discoveries to date have revealed that the origin of some of the later Cretaceous dinosaurs may lie in Cedar Mountain, but further work is needed to understand

920-506: The Mussentuchit Member. Possible indeterminate hesperornithiformes present in the Mussentuchit Member. cf. Acrocanthosaurus Morrison Formation 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

966-607: The North American Continental Plate drifted westward. A middle dinosaur assemblage may be present, but the fossil record is not clear. The Cedar Mountain Formation is sandwiched between the Morrison Formation below and the Naturita Formation and Mancos Shale above. The youngest date for Morrison just below the Cedar Mountain Formation is 135.10 ± 0.30 Ma or Berriasian–Valanginian. The Jurassic-Cretaceous boundary in western North America

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1012-780: The Oklahoma Museum of Natural History, the Denver Museum of Nature & Science, Utah State University-Eastern (formerly College of Eastern Utah), the Utah Geological Survey, Brigham Young University, and Dinosaur National Monument staff. This research indicates that at least two, possibly three dinosaur assemblages are contained within the formation. The oldest of these assemblages is from the Yellow Cat, Poison Strip and basal Ruby Ranch members. The small, Ornitholestes -like theropod Nedcolbertia and

1058-676: 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

1104-466: 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 . The Morrison Formation is subdivided into several members,

1150-561: The brachiosaurid sauropod Cedarosaurus may be considered as relics, with their closest relatives in the Morrison Formation. In contrast, the polacanthid ankylosaur Gastonia and a yet unnamed iguanodontid are similar to related forms from the Lower Cretaceous of southern England. These dinosaurs show that the connection between North America and Europe still existed during the Barremian. All of this changes, however, with

1196-476: 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. 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

1242-649: 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. 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 , Ceratosaurus , Torvosaurus , Saurophaganax , Camptosaurus , Ornitholestes , several stegosaurs comprising at least two species of Stegosaurus and

1288-518: The encroaching Western Interior Seaway . The Naturita is not uniformly distributed and was eroded away in places by the advancing Seaway so that the marine shales of the Mancos Formation lay directly on the Mussentuchit Member or its equivalent. The name Dakota Formation has been improperly used for these strata. Only recently did the 125 m (410 ft) thick formation get subdivided into smaller, distinctive beds called members. There

1334-583: The large body mass of the sauropods has been interpreted as an adaptation to migration in times of drought. 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 ,

1380-580: The occurrence of which are varied across the geographic extent of the Morrison. Members are (in alphabetical order): Other informal or disused designations of the Morrison include the Stockett Bed in Montana, an unofficial sub-unit which contains bituminous coal; the outdated terms Casamero, Chavez, and Prewitt Sandstone for the Brushy Basin, Recapture, and Westwater Canyon, respectively; and

1426-415: The outside of the ribs; in some cases, these plates mineralized and were fossilized. The function of these intercostal plates is unknown. They have been found with Hypsilophodon , Nanosaurus , Parksosaurus , Talenkauen , Thescelosaurus , and Macrogryphosaurus to date. The early ornithopods were only about 1 metre (3 feet) long, but probably very fast. They had a stiff tail, like

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1472-537: The paraphyletic nature of Hypsilophodontidae . A 2017 study which named and described Burianosaurus noted that the type species Iguanodon bernissartensis must be part of the definition, and that the 2005 definition would, in their analysis, include a far larger group than intended (including Marginocephalia ). They proposed an entirely new, node-based definition: the last common ancestor of Iguanodon bernissartensis , Dryosaurus altus , Rhabdodon priscus , and Tenontosaurus tilletti . In 2021, Iguanodontia

1518-602: The right arm and leg. Iguanacolossus I. fortis Iguanodon I. ottingeri A dubious taxon. Planicoxa P. venenica An ilium, cervical neural arch, dorsal vertebral arches, dorsal centra, dorsal rib fragments, sacral vertebra, caudal centra, humerus, ulna, femora, tibiae, metatarsal, and pedal phalanx Tenontosaurus Various partial specimens. Abydosaurus A. mcintoshi cf. Astrodon Indeterminate Brontomerus B. mcintoshi Cedarosaurus C. weiskopfae Articulated dorsal vertebrae, caudal vertebrae, chevrons, proximal portions of

1564-740: The scapulae, coracoids, sternal plates, right humerus, radius and ulna, metacarpal IV, right pubis, partial pubis, proximal portions of ischia, partial femurs, tibia, metatarsals, phalanx, unguals, ribs, and numerous gastroliths. Mierasaurus M. bobyoungi Moabosaurus M. utahensis [Eighteen] braincases, premaxillas, maxillas, dentaries, postorbital, quadrate, cervical vertebrae, dorsal vertebrae, caudal vertebrae, cervical ribs, ribs, sacrum, sternal plate, humerus, ulna and femur. Venenosaurus V. dicrocei Disarticulated caudal vertebrae, scapula, radius, ulna, metacarpals, manus phalanges, pubis, ischium, metatarsals, astragalus, chevrons, and ribs. Indeterminate allosauroid material present in

1610-470: The scientific literature, though many traditional "iguanodontids" are now included in the more inclusive group Hadrosauroidea . Iguanodontia was originally phylogenetically defined, by Paul Sereno , in 1998, as the most inclusive group containing Parasaurolophus walkeri but not Hypsilophodon foxii . Later, in 2005, he amended the definition to include Thescelosaurus neglectus as a secondary external specifier, alongside Hypsilophodon , accounting for

1656-503: 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. However,

1702-502: 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

1748-617: The timing and effects the changing position of the North American Plate had on dinosaurian evolution. Also needed is a better understanding of the effects that the changing North American Plate had on the non-dinosaur vertebrates. The Cedar Mountain Formation is one of the last major dinosaur-bearing formations to be studied in the United States. Although sporadic bone fragments were known before 1990, serious research did not begin until that year. Since then, several organizations have conducted fieldwork collecting dinosaurs, chiefly

1794-932: 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

1840-543: 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: The Morrison Formation contains uranium deposits, including

1886-410: The upper dinosaur assemblage from the top of the Ruby Ranch and Mussentuchit members. This upper assemblage shows greater similarities with Asian dinosaur assemblages from the same time. The upper assemblage also has a tyrannosauroid , a ceratopsian , and a pachycephalosaur . Although not a dinosaur, the primitive mammal Gobiconodon is known from both Mongolia and the Mussentuchit Member. Evidence for

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1932-670: The westward drift of North America, and its connection with Asia 10 to 15 million years later. Data from Carpenter (2006), Cifelli et al. (1999), Kirkland and Madsen (2007), and The Paleobiology Database . A large sail-backed iguanodont represented by large vertebrae and fragmentary remains from the Upper Yellow Cat Member. Cedrorestes C. crichtoni Eolambia E. caroljonesa Hippodraco H. scutodens A nearly complete, disarticulated skull, cervical, dorsal, sacral, and caudal vertebrae, ribs and haemal arches, partial pectoral and pelvic girdles, and

1978-508: Was considered one of the four definite orders of dinosaurs, the others being Theropoda , Sauropoda , and Stegosauria ( Hallopoda was considered a possible fifth). He subdivided the order into three families: Camptonotidae , Iguanodontidae , and Hadrosauridae ; the former was a new name, whereas the latter two were carried over from the nomenclatures of Huxley and Edward Drinker Cope respectively. Within Camptonotidae he included

2024-590: Was given a formal definition under the PhyloCode : "The smallest clade containing Dryosaurus altus , Iguanodon bernissartensis , Rhabdodon priscus , and Tenontosaurus tilletti , provided that it does not include Hypsilophodon foxii ." Under this revised definition, Iguanodontia is limited to its traditionally included species, and if it were found to include hypsilophodonts, which were not traditionally considered iguanodontians, it would become an invalid grouping. The slightly less inclusive clade Dryomorpha

2070-613: Was named by Paul Sereno in 1986 and given a formal definition in the PhyloCode as "the smallest clade containing Dryosaurus altus and Iguanodon bernissartensis ". This group includes basal members such as Hesperonyx , members of the family Dryosauridae , and the derived clade Ankylopollexia . In 2021, Ornithopoda was given a formal definition under the PhyloCode : "The largest clade containing Iguanodon bernissartensis but not Pachycephalosaurus wyomingensis and Triceratops horridus ." The cladogram below follows

2116-599: Was the progressive development of a chewing apparatus that became the most sophisticated ever developed by a non-avian dinosaur, rivaling that of modern mammals such as the domestic cow . They reached their apex of diversity and ecological dominance in the hadrosaurids (colloquially known as 'duck-bills'), before they were wiped out by the Cretaceous–Paleogene extinction event along with all other non- avian dinosaurs . Members are known worldwide. In 1870, Thomas Henry Huxley listed Iguanodontidae (coined by Cope

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