Cedar Mountain Formation Explained

Cedar Mountain Formation
Type:Geological formation
Age:Late Berriasian-Cenomanian
~
Period:Early Cretaceous
Prilithology:Conglomerate, sandstone, mudstone
Namedfor:Cedar Mountain
Namedby:William Stokes
Year Ts:1944
Coordinates:39.25°N -110.824°W
Paleocoordinates:40.2°N -69°W
Subunits:See text
Underlies:Naturita Formation
Overlies:Morrison Formation
Thickness:Varies, some sections over 1000 metres

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.

Geology

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.

Stratigraphy

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[1] or Berriasian–Valanginian. 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 Member or its equivalent. The name Dakota Formation has been improperly used for these strata.[2]

Formation members

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.

Fossil content

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 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.

Dinosaurs

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 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 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 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 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, 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.

Ankylosaurs

Ankylosaurs reported from the Cedar Mountain Formation
GenusSpeciesLocationMemberMaterialNotesImages
AnimantarxA. ramaljonesi
  • Mussentuchit Member
A partial skull and right mandible, cervical vertebrae, dorsal vertebrae, ribs, scapulacoracoids, fragment of sternal plate, humerus, left ilium with ischium, and femur.
CedarpeltaC. bilbeyhallorum
  • Mussentuchit Member
[Two] skulls, cervical vertebrae, dorsal vertebrae, synsacrum, caudal vertebrae, humeri, ulna, ischium, partial right ischium, fragments of the right ilium, cervical ribs, metacarpals, phalanges, unguals, coracoid, femur, tibia, and osteoderms.Cedarpelta was not from the Ruby Ranch Member as initially described.
GastoniaG. burgei
  • Upper Yellow Cat Member
A skull, maxillary tooth, ischium, caudal vertebrae, scapulocoracoid, scapula, ilium, femurs, ulna, humerus, tibia, anterior dorsal vertebra, caudal spines, shoulder spines, caudal plates, osteoderms, and portions of sacral shield.A polacanthine nodosaurid.
G. lorriemcwhinneyae
  • Poison Strip Member
A skull roof, braincase, partial cranium, quadrate, cervical vertebrae, dorsal vertebrae, dorsal rib, synsacrum, caudal vertebrae, chevrons, scapulocoracoid, scapulae, coracoid, humerus, ulna, ilia, ischium, ischia, pubis, femur, fibula, tibia, and osteoderms.A polacanthine nodosaurid.
PeloroplitesP. cedrimontanus
  • Mussentuchit Member
A partial skull, cervical vertebrae, dorsal vertebrae, synsacrum, caudal vertebrae, chevron, scapulacoracoids, humeri, radii, ulnae, ilia, pubis, ischium, femora, tibiae, fibula, metacarpals, metatarsal, metapodials, phalanges, unguals, osteoderms, and fragments.A polacanthine nodosaurid.
cf. SauropeltaIndeterminate
  • Poison Strip Member
Caudal vertebrae, dorsal vertebrae, ribs, and osteoderms.cf. Sauropelta sp. may, instead, represent a large polacanthine.

Neornithischians

A large sail-backed iguanodont represented by large vertebrae and fragmentary remains from the Upper Yellow Cat Member.

Neornithischians reported from the Cedar Mountain Formation
GenusSpeciesLocationMemberMaterialNotesImages
CedrorestesC. crichtoni
  • Upper Yellow Cat Member
Fragments of ribs, fused sacrum, ilium, preacetabular process of an ilium, tibia, metatarsal, and ossified tendons.A basal styracostern ornithopod.
EolambiaE. caroljonesa
  • Mussentuchit Member
Predentaries, dentaries, surangulars, premaxillae, nasal, maxillae, jugals, postorbitals, quadrates, spuamosal, braincases, frontals, parietal, supraoccipital, opisthotic-exoccipital, prootic, laterosphenoid, parasphenoid-basisphenoid, basioccipital, cervical vertebrae, dorsal vertebrae, caudal vertebrae, cervical ribs, dorsal ribs, sacral vertebrae, chevrons, sternal, scapula, coracoid, humerus, ulna, radius, metacarpals, manual phalanges, ilium, pubis, ischium, femur, tibia, fibula, tarsus, metatarsals, and pedal phalanges.A basal hadrosauromorph ornithopod.
Fona[3] F. herzogae
  • Mussentuchit Member
Multiple fairly complete, partially articulated skeletons including cranial materialA thescelosaurine thescelosaurid.
HippodracoH. scutodens
  • Upper Yellow Cat Member
Partial skull, cervical vertebrae, dorsal vertebrae, dorsal rib, partial sacrum, sternal, scapula, humerus, ischium, femur, tibia, astragalus, calcaneum, distal tarsal, phalanxes, and metatarsals.A basal styracostern ornithopod.
IaniI. smithi
  • Lower Mussentuchit Member
A nearly complete, disarticulated skull, cervical, dorsal, sacral, and caudal vertebrae, ribs and haemal arches, partial pectoral and pelvic girdles, and the right arm and leg.A basal rhabdodontomorph ornithopod.
IguanacolossusI. fortis
  • Lower Yellow Cat Member
Partial dentary, maxilla, squamosal, quadrates, axial neural arch, dorsal vertebrae, dorsal rib, caudal vertebrae, chevrons, scapula, ilium, pubis, fibula, and metatarsals.A basal styracostern ornithopod.
IguanodonI. ottingeri
  • Yellow Cat Member
An upper jaw fragment and two teeth.A dubious taxon.
PlanicoxaP. venenica
  • Poison Strip Member
An ilium, cervical neural arch, dorsal vertebral arches, dorsal centra, dorsal rib fragments, sacral vertebra, caudal centra, humerus, ulna, femora, tibiae, metatarsal, and pedal phalanxA basal styracostern ornithopod.
TenontosaurusIndeterminate
  • Lower Ruby Ranch Member
Various partial specimens.[4] Remains have also been found in the Upper Ruby Ranch Member and the Mussentuchit Member.

Sauropods

Sauropods reported from the Cedar Mountain Formation
GenusSpeciesLocationMemberMaterialNotesImages
AbydosaurusA. mcintoshi
  • Mussentuchit Member
[Two] nearly complete skulls, braincase with a partial skull roof, cervical vertebrae, partial pelvis and sacrum with articulated caudal vertebrae, scapula, humerus, and metacarpus.A brachiosaurid sauropod.
cf. AstrodonIndeterminate
  • Ruby Ranch Member.
BrontomerusB. mcintoshi
  • Ruby Ranch Member, and possibly the upper Yellow Cat Member
An ilium, crushed presacral centrum, mid-to-posterior caudal vertebra, partial distal caudal centrum, anterior dorsal rib, nearly complete scapula missing anterior portion, partial sternal plates, and other fragments.A dubious camarasauromorph.
CedarosaurusC. weiskopfae
  • Upper Yellow Cat Member, and possibly also the lower Yellow Cat Member
Articulated dorsal vertebrae, caudal vertebrae, chevrons, proximal portions of 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. A brachiosaurid sauropod.
MierasaurusM. bobyoungi
  • Lower Yellow Cat Member
A partial skull and jaw, teeth, cervical vertebrae, cervical ribs, dorsal vertebrae, dorsal ribs, sacral ribs, caudal vertebrae, chevrons, scapulae, radius, ulna, manus, complete pelvic elements, femora, tibia, fibula, astragalus pes, a possible juvenile dentary, and juvenile femur.One of the last-surviving members of turiasauria.
MoabosaurusM. utahensis
  • Upper Yellow Cat Member
[Eighteen] braincases, premaxillas, maxillas, dentaries, postorbital, quadrate, cervical vertebrae, dorsal vertebrae, caudal vertebrae, cervical ribs, ribs, sacrum, sternal plate, humerus, ulna and femur.One of the last-surviving members of turiasauria.
VenenosaurusV. dicrocei
  • Poison Strip Member
Disarticulated caudal vertebrae, scapula, radius, ulna, metacarpals, manus phalanges, pubis, ischium, metatarsals, astragalus, chevrons, and ribs.A brachiosaurid sauropod.

Theropods

Indeterminate allosauroid material present in the Lower Yellow Cat and Ruby Ranch Members. Indeterminate dromaeosaurine present in the Mussentuchit Member. Indeterminate deinonychosaurian remains present in the Mussentuchit member.[5] 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 the Mussentuchit Member. Possible indeterminate hesperornithiformes present in the Mussentuchit Member.

Theropods reported from the Cedar Mountain Formation
GenusSpeciesLocationMemberMaterialNotesImages
cf. AcrocanthosaurusIndeterminate
  • Ruby Ranch Member.
An isolated tooth.May represent a similar taxon instead based on the morphology of the tooth.
DeinonychusIndeterminate
  • Mussentuchit Member.
FalcariusF. utahensis
  • Lower Yellow Cat Member.
Numerous elements belonging to immature and mature individuals.A basal therizinosaur theropod.
GeminiraptorG. suarezarum
  • Lower Yellow Cat Member.
A maxilla.A troodontid theropod.
MartharaptorM. greenriverensis
  • Upper Yellow Cat Member.
A cervical neural arch, cranial dorsal vertebra, distal caudal centrum, ulna?, radius, scapula, ischium, distal pubis?, metacarpal, manual phalanxes, manual unguals, metatarsals, pedal phalanxes and pedal unguals.A possible therizinosauroid therizinosaur.
MorosM. intrepidus
  • Mussentuchit Member.
Portions of the femur, tibia, metatarsals and phalanges.A pantyrannosaurian tyrannosauroid.
NedcolbertiaN. justinhofmanni
  • Upper Yellow Cat Member.
"Partial skeletons of [three] individuals."A basal ornithomimosaur.
cf. RichardoestesiaIndeterminate
  • Mussentuchit Member.
Teeth.An indeterminate coelurosaur.
SiatsS. meekerorum
  • Mussentuchit Member.
Dorsal vertebrae, partial ilium and ischium, partial fibula, caudal vertebrae, a chevron, a pedal phalanx and several indeterminate bone fragments.A neovenatorid allosauroid.
UtahraptorU. ostrommaysi
  • Upper Yellow Cat Member.
Pedal unguals, tibia, femur, premaxillae, nasal, quadratojugal, caudal vertebrae, cervical vertebrae, dorsal vertebrae, sacral vertebrae, proximal caudal vertebrae, coracoid, partial ilium, incomplete ischium, femora, astragalus, metatarsal, phalanxes and undescribed material. A dromaeosaurine dromaeosaurid.
Indeterminate
  • Poison Strip Member.
Pelvic element?
YurgovuchiaY. doellingi
  • Lower Yellow Cat Member.
Cervical vertebrae, dorsal vertebrae, caudal vertebrae, and the proximal end of a pubis.A dromaeosaurine dromaeosaurid.

Other vertebrate fossils

Besides dinosaurs, the Cedar Mountain Formation has produced a wealth of small fossils (a.k.a. microfossils), mostly teeth from a variety of vertebrates. Most of these specimens have been found in the Mussentuchit Member where they are collected by washing the rock through fine window screen. The teeth and other small fossils are picked from the residue.

The various vertebrates are listed by member in the list below.

Non-vertebrate fossils are more widely distributed in the Cedar Mountain Formation. These include the distinctive reproductive structures of fresh water algae that are called charophytes. Charophytes are so distinctive that they are used to correlate strata of similar age, and thus were used to show that the Yellow Cat Member was time equivalent to Barremian age strata in England. Ostracods, small crustaceans with clam-like shells, also occur in fresh water deposits, along with "finger-clams" or conchostracans. Pollen have been found in the Mussentuchit Member and are important for reconstructing the environment. In a few places, large petrified logs are known, especially from the Poison Strip. These conifer logs are over a meter in diameter and indicate the presence of trees over 30 m (100 feet). The distinct wood of the tree fern Tempskya is occasional found as well.

Data from Carpenter (2006), Cifelli et al. (1999), Kirkland and Madsen (2007), and The Paleobiology Database.

Other reptiles

Indeterminate isolated pterosaur remains have been recovered from the Yellow Cat and Mussentuchit Members.

A partial neochoristodere femur is known from the Yellow Cat Member.[6]

Crurotarsans

Indeterminate crocodilian remains present in the Yellow Cat and Ruby Ranch Members. Indeterminate pholidosaurid remains present in the Mussentuchit Member. Indeterminate atoposaurid remains present in the Mussentuchit Member.

Crurotarsans of the Cedar Mountain Formation
GenusSpeciesLocationMemberAbundanceDescriptionImages
cf. Bernissartiacf. Bernissartia sp.
  • Mussentuchit Member
DakotasuchusDakotasuchus kingi
  • Mussentuchit Member.
Lepidosaurs
Lepidosaurs of the Cedar Mountain Formation
GenusSpeciesLocationMemberAbundanceDescriptionImages
ToxolophosaurusToxolophosaurus sp.
  • Yellow Cat Member.
HarmodontosaurusHarmodontosaurus emeryensis
  • Mussentuchit Member.
DimekodontosaurusDimekodontosaurus madseni
  • Mussentuchit Member.
DicothodonDicothodon moorensis
  • Mussentuchit Member.
PseudosaurillusPseudosaurillus sp.
  • Mussentuchit Member.
BicuspidonBicuspidon numerosus
  • Mussentuchit Member.
BothriagenysBothriagenys mysterion
  • Mussentuchit Member.
PrimadermaPrimaderma nessovi
  • Mussentuchit Member.
ConiophisConiophis sp.
  • Mussentuchit Member.
Turtles

Indeterminate baenid remains present in the Mussentuchit Member.

Turtles of the Cedar Mountain Formation
GenusSpeciesLocationMemberAbundanceDescriptionImages
GlyptopsGlyptops sp.
  • Yellow Cat Member
  • Mussentuchit Member
NaomichelysNaomichelys sp.
  • Mussentuchit Member.
gen. nov.sp. nov.
  • Yellow Cat Member

Amphibians

Indeterminate anuran remains present in the Mussentuchit Member.

Fish

Bony fish

Indeterminate amiiform present in the Yellow Cat and Mussentuchit Members. Indeterminate neopterygian remains present in the Mussentuchit Member. Possible indeterminate pycnodontid remains present in the Mussentuchit Member. Possible indeterminate lepisosteid remains present in the Mussentuchit Member.

Bony fishes of the Cedar Mountain Formation
GenusSpeciesLocationMemberAbundanceDescriptionImages
Semionotus?Semionotus? sp.
  • Yellow Cat Member
CeratodusC. kempae
  • Yellow Cat Member
C. kirklandi
  • Yellow Cat Member
C. molossus
  • Mussentuchit Member
Cartilaginous fish

A new genus and species of orectolobid present in the Mussentuchit Member.

Cartilaginous Fishes of the Cedar Mountain Formation
GenusSpeciesLocationMemberAbundanceDescriptionImages
HybodusHybodus sp.
  • Ruby Ranch Member
  • Mussentuchit Member
PolyacrodusPolyacrodus parvidens
  • Mussentuchit Member
LissodusLissodus sp.
  • Mussentuchit Member
IschyrhizaIschyrhiza sp.
  • Mussentuchit Member
PseudohypolophusPseudohypolophus sp.
  • Mussentuchit Member
cf. BaibishaNew species
  • Mussentuchit Member
CretorectolobusIndeterminate
  • Mussentuchit Member

Mammaliaformes

New genus and species of pappotheriid present in the Mussentuchit Member. Indeterminate genus and species of picopsid present in the Mussentuchit Member.

Mammals of the Cedar Mountain Formation
GenusSpeciesLocationMemberAbundanceDescriptionImages
AmeribaatarAmeribaatar zofiae
  • Mussentuchit
An unspecified multituberculate.
AstroconodonAstroconodon delicatus
  • Mussentuchit
A predatory triconodont with a debate on whether it was fully terrestrial or semiaquatic.
BryceomysBryceomys intermedius
  • Mussentuchit
An unspecified multituberculate, probably a cimolodont.
CedaromysCedaromys bestia
  • Mussentuchit
Cedaromys parvus
  • Mussentuchit
CifelliodonCifelliodon wahkermoosuch
  • Yellow Cat Member
a haramiyidan mammaliaform
CorviconodonCorviconodon utahensis
  • Mussentuchit
DakotadensDakotadens pertritus
  • Mussentuchit
JanumysJanumys erebos
  • Mussentuchit
JugulatorJugulator amplissimus
  • Mussentuchit
KokopelliaKokopellia juddi
  • Mussentuchit
Possible metatherian
ParacimexomysParacimexomys perplexus
  • Mussentuchit
Paracimexomys robisoni
  • Mussentuchit
SpalacolestesSpalacolestes cretulablatta
  • Mussentuchit
Spalacolestes inconcinnus
  • Mussentuchit
SpalacotheridiumSpalacotheridium noblei
  • Mussentuchit

See also

References

Bibliography and further reading

Further reading

External links

Notes and References

  1. Joeckel . Robert M. . Suarez . Celina A. . McLean . Noah M. . Möller . Andreas . Ludvigson . Gregory A. . Suarez . Marina B. . Kirkland . James I. . Andrew . Joseph . Kiessling . Spencer . Hatzell . Garrett A. . February 2023 . Berriasian–Valanginian Geochronology and Carbon-Isotope Stratigraphy of the Yellow Cat Member, Cedar Mountain Formation, Eastern Utah, USA . Geosciences . en . 13 . 2 . 32 . 10.3390/geosciences13020032 . 2076-3263. free . 2023Geosc..13...32J . 1808/34140 . free .
  2. Carpenter, K., 2014. Where the sea meets the land—the unresolved Dakota problem in Utah. Utah Geological Association Publication, 43, pp.357-372.
  3. Avrahami . Haviv M. . Makovicky . Peter J. . Tucker . Ryan T. . Zanno . Lindsay E. . 2024-07-09 . A new semi-fossorial thescelosaurine dinosaur from the Cenomanian-age Mussentuchit Member of the Cedar Mountain Formation, Utah . . en . 10.1002/ar.25505 . 1932-8486. free .
  4. Web site: EARLY CRETACEOUS DINOSAURS OF UTAH . Utah Geological Society . 21 March 2021.
  5. Britt, Brooks B. Chure, Daniel, Currie, Philip, Holmes, Aaron, Theurer, Brandon, Scheetz, Rodney. (2021). A NEW DEINONYCHOSAURIAN THEROPOD FROM THE MID-CRETACEOUS (ALBIAN) MUSSENTUCHIT MEMBER OF THE CEDAR MOUNTAIN FORMATION IN DINOSAUR NATIONAL MONUMENT, NORTH EASTERN UTAH, USA. The Society of Vertebrate Paleontology.
  6. Britt . Brooks B. . Scheetz . Rodney D. . Brinkman . Donald B. . Eberth . David A. . 2006-12-11 . A Barremian neochoristodere from the Cedar Mountain Formation, Utah, U.S.A. . Journal of Vertebrate Paleontology . en . 26 . 4 . 1005–1008 . 10.1671/0272-4634(2006)26[1005:ABNFTC]2.0.CO;2 . 86258448 . 0272-4634.