Cedar Mountain Formation

The Cedar Mountain Formation is the name given to a distinctive sedimentary geologic formation in eastern Utah. The formation was named for Cedar Mountain in northern Emery County, Utah, where William Lee Stokes first studied the exposures in 1944.CedrorestesCedrorestes crichtoniEolambiaEolambia caroljonesaHippodracoHippodraco scutodensIguanacolossusIguanacolossus fortisIguanodonIguanodon ottingeri'Teeth.'Dubious.PlanicoxaPlanicoxa venenica'Associated postcranium.'TenontosaurusTenontosaurus tilettiZephyrosaurusZephyrosaurus schaffiAbydosaurusAbydosaurus mcintoshicf. AstrodonIndeterminateBrontomerusBrontomerus mcintoshiCedarosaurusCedarosaurus weiskopfae'Postcranial skeleton.'MierasaurusMierasaurus bobyoungiMoabosaurusMoabosaurus utahensis'Remains of at least 18 fragmentary individuals.'VenenosaurusVenenosaurus dicrocei'Partial postcranial skeleton.'cf. AcrocanthosaurusIndeterminateDeinonychusIndeterminateFalcariusFalcarius utahensisGeminiraptorGeminiraptor suarezarumMartharaptorMartharaptor greenriverensisMorosMoros intrepidusNedcolbertiaNedcolbertia justinhofmanni'Partial skeletons of individuals.'cf. RichardoestesiaIndeterminateSiatsSiats meekerorumUtahraptorUtahraptor ostrommaysi'Skull and postcranial fragments.'IndeterminateYurgovuchiaYurgovuchia doellingicf. Bernissartiacf. Bernissartia sp.DakotasuchusDakotasuchus kingiToxolophosaurusToxolophosaurus sp.HarmodontosaurusHarmodontosaurus emeryensisDimekodontosaurusDimekodontosaurus madseniDicothodonDicothodon moorensisPseudosaurillusPseudosaurillus sp.BothriagenysBothriagenys mysterionPrimadermaPrimaderma nessoviConiophisConiophis sp.GlyptopsGlyptops sp.NaomichelysNaomichelys sp.AlbanerpetonAlbanerpeton cf. A. nexuosusSemionotus?Semionotus? sp.CeratodusC. kempaeC. kirklandiC. molossusHybodusHybodus sp.PolyacrodusPolyacrodus parvidensLissodusLissodus sp.IschyrhizaIschyrhiza sp.PseudohypolophusPseudohypolophus sp.cf. BaibishaNew speciesCretorectolobusIndeterminateAmeribaatarAmeribaatar zofiaeAstroconodonAstroconodon delicatusBryceomysBryceomys intermediusCedaromysCedaromys bestiaCedaromys parvusCifelliodonCifelliodon wahkermoosucha haramiyidan mammaliaformCorviconodonCorviconodon utahensisDakotadensDakotadens pertritusJanumysJanumys erebosJugulatorJugulator amplissimusKokopelliaKokopellia juddiPossible metatherianParacimexomysParacimexomys perplexusParacimexomys robisoniSpalacolestesSpalacolestes cretulablattaSpalacolestes inconcinnusSpalacotheridiumSpalacotheridium noblei The Cedar Mountain Formation is the name given to a distinctive sedimentary geologic formation in eastern Utah. The formation was named for Cedar Mountain in northern Emery County, Utah, where William Lee Stokes first studied the exposures in 1944. 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 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 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 148.1 ± 0.5 Ma . or lower Tithonian. Typically, the Jurassic-Cretaceous boundary in western North America 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 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 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 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 the Mussentuchit Member. Each of these members are named after a geographic area where they were first studied.