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Hell Creek Formation

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Hell Creek Formation
Stratigraphic range: Maastrichtian–Danian, 66.8–66 Ma
Exposure in the badlands in the vicinity of Fort Peck Reservoir
TypeGeological formation
UnderliesFort Union Formation
OverliesFox Hills Formation
Lithology
PrimaryClaystone, mudstone
OtherSandstone
Location
RegionMontana, North Dakota,
South Dakota, Wyoming
Type section
Named forHell Creek, Jordan, Montana
Paleontological camp of Museum of the Rockies in eastern Montana - Hell Creek Formation (summer dig season 2009).

The Hell Creek Formation is an intensively-studied division of mostly Upper Cretaceous and some lower Paleocene rocks in North America, named for exposures studied along Hell Creek, near Jordan, Montana. The formation includes portions of Montana, North Dakota, South Dakota, and Wyoming. In Montana, the Hell Creek Formation overlies the Fox Hills Formation. The site of Pompeys Pillar National Monument is a small isolated section of the Hell Creek Formation.

It is a series of fresh and brackish-water clays, mudstones, and sandstones deposited during the Maastrichtian and Danian (respectively, the end of the Cretaceous period and the beginning of the Paleogene) by fluvial activity in fluctuating river channels and deltas and very occasional peaty swamp deposits along the low-lying eastern continental margin fronting the late Cretaceous Western Interior Seaway. The climate was mild, and the presence of crocodilians suggests a sub-tropical climate, with no prolonged annual cold. The famous iridium-enriched Cretaceous–Paleogene boundary, which separates the Cretaceous from the Cenozoic, occurs as a discontinuous but distinct thin marker bedding above and occasionally within the formation, near its boundary with the overlying Fort Union Formation.

The world's largest collection of Hell Creek fossils is housed and exhibited at the Museum of the Rockies, in Bozeman, Montana. The specimens displayed are the result of the museum's Hell Creek Project, a joint effort between the museum, Montana State University, the University of Washington,[1] the University of California, Berkeley, the University of North Dakota, and the University of North Carolina which began in 1998.

Geology

Map of the Hell Creek and Lance Formations in western North America

The Hell Creek Formation in Montana overlies the Fox Hills Formation and underlies the Fort Union Formation, and the boundary with the latter occurs near the Cretaceous-Paleogene boundary, which defines the end of the Cretaceous period and has been dated to 66 ± 0.07 Ma old.[2] Fauna characteristic of the Hell Creek (Lancian land vertebrate age) are found as high as a few meters below the boundary.[3]

The K-Pg boundary is generally situated near the contact between the upper Hell Creek and the lower Ludlow member of the Fort Union Formation, though in some areas (e.g. in North Dakota) the boundary is well within the Ludlow Member, 3 meters above the boundary with the Hell Creek in some areas.[3] On the other hand, in some small regions of Montana, the Hell Creek Formation contains the K-Pg boundary, and extends slightly into the Paleogene.[4]

Paleobiology

Animals of the Hell Creek Formation

Many animals including dinosaurs lived in the Hell Creek Formation. The Hell Creek Formation has world-famous dinosaur fossil sites. Fossils are found of sea creatures from the recession and adjacent inland sea at that time. Vertebrates include dinosaurs, pterosaurs, crocodiles, champsosaurs, lizards, snakes, turtles, frogs and salamanders. Remains of fishes and mammals have also been found in the Hell Creek Formation. The formation has produced impressive assemblages of invertebrates (including Ammonites), plants, mammals, fish, reptiles (including the lizard Obamadon), marine reptiles (including the marine reptiles like mosasaurs, plesiosaurs and sea turtles), and amphibians. Notable dinosaur finds include Tyrannosaurus and Triceratops, ornithomimids as well, caenagnathids like Anzu, a variety of small theropods, pachycephalosaurs, ankylosaurs, crocodylomorphs and squamates, including various animal fossils unearthed in the Hell Creek Formation. The most complete hadrosaurid dinosaur ever found, an Edmontosaurus, was retrieved in 2000 from the Hell Creek Formation and widely publicized in a National Geographic documentary aired in December 2007. A few bird, mammal, and pterosaur fossils have also been found. The teeth of sharks and rays are sometimes found in the riverine Hell Creek Formation, suggesting that some of these taxa were then, as now, tolerant of fresh water. The "Lancian" fauna is more similar overall phylogenetically to East Asian and Canadian/Alaskan faunas than most Campanian North American faunas.

View of Hell Creek State Park, the "heart" of Hell Creek Formation.

Depositional environment

The dominant plants of the Hell Creek Formation are mainly flowering plants.

It is a series of fresh and brackish-water clays, mudstones, and sandstones deposited during the Maastrichtian and Danian (respectively, the end of the Cretaceous period and the beginning of the Paleogene) by fluvial activity in fluctuating channels and deltas and very occasional peaty swamp deposits along the low-lying eastern continental margin fronting the late Cretaceous Western Interior Seaway. The Hell Creek Formation, as typified by exposures in the Fort Peck area of Montana, has been interpreted as a flat, forested floodplain with a relatively subtropical climate that supported a variety of plants ranging from angiosperm trees to conifers such as the bald cypress, ferns and ginkgos. The Hell Creek Formation was laid down by streams, on a coastal plain along the edge of the Western Interior Seaway. The presence of crocodilia suggests climate was subtropical; there was no cold season and probably ample precipitation.

The Hell Creek Formation, Lance Formation and Scollard Formation represent different sections of the western shore of the shallow sea that divided western and eastern North America during the Cretaceous. Swampy lowlands were the habitat of various animals, including dinosaurs. A broad coastal plain extended westward from the seaway to the newly formed Rocky Mountains. These formations are composed largely of sandstone and mudstone which have been attributed to floodplain, fluvial, lacustrine, swamp, estuarine and coastal plain environments.[5][6][7] Hell Creek is the best studied of these ancient environments. At the time, this region was subtropical, warm and moist climate. The climate was humid, with flowering plants, conifers, palmettos, and ferns in the swamps, and conifers, canopy, understory plants, Ash trees, live oak and shrubs in the forests. In northwestern South Dakota, strips of black layers deposited in the wetland environment are rich in coal, and a bright band-like layer of sand and mud from the river floodplain accumulated. Many plant species were supported, primarily angiosperms, and less commonly conifers, bald cypress, ferns and cycads. An abundance of fossil leaves are found at dozens of different sites indicating that the area was largely forested by small trees.

Invertebrates

Invertebrates reported from the Hell Creek Formation
Genus Species Location Stratigraphic position Material Notes Images

Plesielliptio

P. postbiplicatus

Fresh water Pelecypod.

P. gibbosoides

P. whitfieldi

Rhabdotophorus

R. aldrichi

Pleurobema

P. cryptorhynchus

Plethobasus

P. aesopiformis

P. biesopoides

Quadrula

Q. cylindricoides

Proparreysia

P. verrucosiformis

P. holmesiana

P. barnumi

P. percorrugata

P. pyramidatoides

P. letsoni

P. retusoides

P. corbiculoides

P. paucinodosa

Obovaria?

O?. pyramidella

Corbicula

C. cf. subelliptica

C. sp

From a marine facies ("tongue") in South Dakota. Modern members of this genus live in fresh water

Sphaerium

S. beckmani

"Pill clam". "Nut clam". "Fingernail clam". "Pea clam". Family Sphaeriidae.

Pleiodon

Indeterminate

Campeloma

C. sp

Freshwater snail.

Anomia

A. gryphorhyncha

Bivalve. Family Anomiidae. From a marine facies ("tongue") in South Dakota.

Crassostrea

C. subtrigonalis

Oyster. Family Ostreidae. Collected from a marine facies ("tongue") in South Dakota.

Granocardium

G. sp

Bivalve. Family Cardiidae (cockle). Collected from a marine facies ("tongue") in South Dakota.

Hiatella?

H. sp

Bivalve. Present members of this genus are rock borers. Collected from a marine facies ("tongue") in South Dakota.

Leptosolen

indeterminate

Bivalve. Family Cultellidae. Collected from a marine facies ("tongue") in South Dakota.

Sphenodiscus

S. lenticularis

Ammonite. From a marine facies ("tongue") in South Dakota.

Discoscaphites

D. rossi

Microconch of an ammonite. From a marine facies ("tongue") in South Dakota.

Scaphitidae

indeterminate

Ammonite. From a marine facies ("tongue") in South Dakota. Other attributes: specimen has hooks on its shell.

Cephaloleichnites

C. strongi

hispine beetle. ("leaf beetle")

Amphibians

Color key
Taxon Reclassified taxon Taxon falsely reported as present Dubious taxon or junior synonym Ichnotaxon Ootaxon Morphotaxon
Notes
Uncertain or tentative taxa are in small text; crossed out taxa are discredited.
Amphibians reported from the Hell Creek Formation
Genus Species State Stratigraphic position Material Notes Images

Anura (frog)[8]

indeterminate[8]

  • North Dakota[9]
  • South Dakota[9]

Middle to upper Hell Creek Formation[10]

3 unassigned specimens[11]

Anura indet. consists of material not currently assigned to any genus of frog.[8]

Barbourula[12]

Indeterminate[13]

Caudata (salamander)[8]

indeterminate[8]

  • North Dakota[9]
  • South Dakota[9]

Lower to uppermost Hell Creek Formation[10]

149 unassigned specimens[11]

Material of Caudata indet. is not currently assigned to any genus.[8]

Eopelobates[15]

Indeterminate[13]

Habrosaurus[8][13]

H. dilatus[8][13]

Middle to upper Hell Creek Formation[10]

6 specimens[11]

Habrosaurus is a sirenid amphibian.[8]

Lisserpeton[13]

L. bairdi[13]

Opisthotriton[8][13]

O. kayi[8][13]

Lower to upper Hell Creek Formation[10]

22 specimens[11]

Opisthotriton is classified as a Batrachosauroididae.[8]

Paranecturus[16]

P. garbanii[16]

A member of Proteidae.[16]

Proamphiuma[13]

P. cretacica[13]

Prodesmodon[13]

P. copei[13]

Scapherpeton[8][13]

S. tectum[8][13]

Lower to upper Hell Creek Formation[10]

144 specimens[11]

Scapherpeton is a scapherpetonid that is very common in the Hell Creek Formation.[8]

Scotiophryne[13]

S. pustulosa[13]

A small frog

Fish

Bony fish

Bony fishes reported from the Hell Creek Formation
Genus Species Location Stratigraphic position Material Notes Images

Acipenser[8][17]

A. eruciferus[17]

A sturgeon

cf. A. sp.[8]

  • North Dakota[9]
  • South Dakota[9]

Lower to upper Hell Creek Formation[10]

18 specimens are tentatively assigned to Acipenser sp.[11]

Acipenser sp. is tentatively referred to the genus.[8]

Amia[17]

A. fragosa[17]

small amiid fish (ubiquitous). Closely related to the modern Bowfin

Belonostomus[8][17]

B. longirostris[8][17]

Lower to upper Hell Creek Formation[10]

28 specimens[11]

A long-snouted slender fish classified as an aspidorhynchid.[8]

Coriops[19]

C. amnicolus[19]

Kindleia[8]

K. fragosa[8]

  • North Dakota[9]
  • South Dakota[9]

Lower to uppermost Hell Creek Formation[10]

2610 specimens have been assigned to Kindleia, making it an extremely common genus.[11]

Kindleia is a genus assigned to Amiidae, along with Melvius and Amia.[8]

Lepisosteus[8][17]

L. occidentalis[8][17]

Lower to uppermost Hell Creek Formation[10]

938 specimens are assigned to Lepidosteus[11]

A lepidosteid that is very common in the Hell Creek Formation.[8]

Melvius[8]

M. thomasi[8]

  • North Dakota[9]
  • South Dakota[9]

Lower to upper Hell Creek Formation[10]

6 specimens are assigned to Melvius[11]

A large amiid fish.[8]

Phyllodus

P. paulkatoi

fish with columnar teeth

Palaeolabrus[17]

P. montanensis[17]

Paleopsephurus[17]

P. wilsoni[17]

A paddlefish

Palaeolabrus

P. montanensis

fish (incertae sedis)

Paralbula[21]

P. casei[21]

Platacodon[19]

P. nanus[19]

small teleost fish

Protamia[17]

Indeterminate[17]

Pachyrhizodontoidei

Indeterminate

Fish

Protoscaphirhynchus[17]

P. squamosus[17]

a sturgeon

Cartilaginous fish

Chondrichthyes reported from the Hell Creek Formation
Genus Species Location Stratigraphic position Material Notes Images

Chiloscyllium[22]

C. sp.[22]

A member of Hemiscylliidae.[22]

Lonchidion[23]

L. selachos[23]

Lower to upper Hell Creek Formation[10]

40 specimens[11]

A genus of prehistoric sharks in the family Hybodontidae. It makes up 0.4% of the remains of the vertebrates of the Hell Creek Formation.[8]

Myledaphus[22]

M. pustulosus[22]

Lower to upper Hell Creek Formation.[10]

1677 specimens[11] previously assigned to M. bipartitus.[22]

Is an anacoracid batoid[8] rajiform related to guitarfishes.[22] Described on the basis of teeth formerly assigned to the species M. bipartitus.[22] The material assigned to Myledaphus bipartitus and makes up 16.5% of the vertebrate remains.[8]

Protoginglymostoma[22]

P. estesi[22]

A member of Ginglymostomatidae.[22] Formerly assigned to the genus Brachaelurus.

Restesia[22]

R. americana[22]

Middle Hell Creek Formation[10]

5 specimens previously assigned to Squatirhina[11]

A wobbegong-like shark.[22] Formerly assigned to Squatirhina. The remains consist of 0.05% of the vertebrates.[11] Also known from the Lance Formation.[22]

Dinosaurs

A paleo-population study is one of the most difficult of analyses to conduct in field paleontology. Here is the most recent estimate of the proportions of the eight most common dinosaurian families in the Hell Creek Formation, based on detailed field studies by White, Fastovsky and Sheehan (1998). [citation needed]

  • Ceratopsidae 61%
  • Hadrosauridae 23%
  • Ornithomimidae 5%
  • Tyrannosauridae 4%
  • Hypsilophodontidae 3%
  • Dromaeosauridae 2%
  • Pachycephalosauridae 1%
  • Troodontidae 1% (represented only by teeth)
Pie chart of the time averaged census for large-bodied dinosaurs from the entire Hell Creek Formation in the study area.

Outcrops sampled by the Hell Creek Project were divided into three sections: lower, middle and upper slices. The top and bottom sections were the focus of the PLoS One report, and within each portion many remains of Triceratops, Edmontosaurus, and Tyrannosaurus were found. Triceratops was the most common in each section, but, surprisingly, Tyrannosaurus was just as common, if not slightly more common, than the hadrosaur Edmontosaurus. In the upper Hell Creek section, for example, the census included twenty two Triceratops, five Tyrannosaurus, and five Edmontosaurus.

The dinosaurs Thescelosaurus, Ornithomimus, Pachycephalosaurus and Ankylosaurus were also included in the breakdown, but were relatively rare. Other dinosaurs, such as Sphaerotholus, Denversaurus, Torosaurus, Struthiomimus, Acheroraptor, Dakotaraptor, Pectinodon, Richardoestesia, Paronychodon, Anzu, Leptorhynchos and Troodon, were reported as being rare and are not included in the breakdown.

The dinosaur collections made over the past decade during the Hell Creek Project yielded new information from an improved genus-level collecting schema and robust data set that revealed relative dinosaur abundances that were unexpected, and ontogenetic age classes previously considered rare. We recognize a much higher percentage of Tyrannosaurus than previous surveys. Tyrannosaurus equals Edmontosaurus in U3 and in L3 comprises a greater percentage of the large dinosaur fauna as the second-most abundant taxon after Triceratops, followed by Edmontosaurus. This is surprisingly consistent in (1) the two major lag deposits (MOR loc. HC-530 and HC-312) in the Apex sandstone and Jen-rex sand where individual bones were counted and (2) in two thirds of the formation reflected in L3 and U3 records of dinosaur skeletons only.

Triceratops is by far the most common dinosaur at 40% (n = 72), Tyrannosaurus is second at 24% (n = 44), Edmontosaurus is third at 20% (n = 36), followed by Thescelosaurus at 8% (n = 15), Ornithomimus at 5% (n = 9), and Pachycephalosaurus and Ankylosaurus both at 1% (n = 2) are relatively rare.

Fossil footprints of dinosaurs from the Hell Creek Formation are very rare. As of 2017, there is only one find of a possible Tyrannosaurus rex footprint, dating from 2007 and described a year later.[25]

Ornithischians

Ankylosaurs

Ankylosauria reported from the Hell Creek Formation
Genus Species State Stratigraphic position Material Notes Images

Ankylosaurus[26]

A. magniventris[26]

An ankylosaur. Also found in the Lance and Scollard Formations.

Denversaurus[26]

D. schlessmani [26]

A nodosaurid ankylosaur.

Pachycephalosaurs

An undescribed Pachycephalosaur is present in North Dakota.[28]

Pachycephalosaurs reported from the Hell Creek Formation
Genus Species State Stratigraphic position Material Notes Images

Dracorex[29]

D. hogwartsia[29]

A pachycephalosaur, probably synonymous with Pachycephalosaurus.

Pachycephalosaurus[26]

P. wyomingensis[26]

A pachycephalosaur. Also found in the Lance Formation.

Sphaerotholus[26]

S. buchholtzae[26]

"Skull material."[30]

A pachycephalosaur, possibly synonymous with Prenocephale.

Stygimoloch[26]

S. spinifer[26]

  • Montana[26]
  • South Dakota
  • North Dakota

A pachycephalosaur, probably synonymous with Pachycephalosaurus. Also found in the Lance Formation.

Ceratopsians

Indeterminate ceratopsid specimens are extremely common. 8.31% of all vertebrate remains from the Hell Creek Formation are unassigned ceratopsids.[11] In 2012, a new unidentified species of chasmosaur ceratopsian with noticeable differences from Triceratops was unearthed in South Dakota by a fossil hunter named John Carter.[31][32][33] Despite not having a paper on the new specimen, according to the Prehistoric Times issue no. 121 from Spring 2017, the specimen has been referred to as Duranteceratops.

Color key
Taxon Reclassified taxon Taxon falsely reported as present Dubious taxon or junior synonym Ichnotaxon Ootaxon Morphotaxon
Notes
Uncertain or tentative taxa are in small text; crossed out taxa are discredited.
Ceratopsians reported from the Hell Creek Formation
Genus Species Synonyms State Stratigraphic position Material Notes Images

Leptoceratops[26]

Leptoceratops c.f. gracilis[26]

A small primitive-looking ceratopsian.

Tatankaceratops

T. sacrisonorum

  • South Dakota

A ceratopsian possibly synonymous with Triceratops[34]

Torosaurus[8][26]

T. latus[8][26]

Upper Hell Creek Formation[10]

A ceratopsian possibly synonymous with Triceratops.[35] A rare ceratopsid.[10]

Triceratops[8][26]

T. horridus[8][26]

Lowermost to upper Hell Creek Formation[10]

4 specimens are assigned to Triceratops horridus from the Hell Creek Formation[11]

A ceratopsian.[8] Also found in the Evanston, Frenchman, Lance, Laramie, and Scollard Formations.

T. prorsus[26]

Very common.[citation needed]

Also found in the Frenchman and Lance Formations.

Ornithopods and Parksosaurs

Indeterminate hadrosaurid remains are very common in the Hell Creek Formation.[8] A lambeosaurine hadrosaur similar to Parasaurolophus, possibly an undescribed species, may have lived in the Hell Creek Formation; however, lack of more evidence makes this unclear as lambeosaurine fossils are rare in Hell Creek and in Laramida as a whole.[37][38] However, the lambeosaurines were thriving in Asia and Europe during the end of the Cretaceous.

Ornithopods and Theseclosaurs reported from the Hell Creek Formation
Genus Species Synonyms State Stratigraphic position Material Notes Images

Edmontosaurus

E. annectens

  • Anatosaurus annectens[39]
  • Anatotitan copei[39]
  • Montana[26]
  • South Dakota[27]
  • North Dakota(Mummy Fossil)

Very common.

A hadrosaur. Also found in the Denver, Frenchman, Lance, Laramie, and Scollard Formations.

Thescelosaurus[27]

T. garbanii[40]

  • Bugenasaura garbanii

T. infernalis

  • Bugenasaura infernalis

Nomen dubium

T. neglectus[8][27]

Lower to upper Hell Creek Formation[10]

50 specimens[11]

A small ornithopod. Also found in the Frenchman, Lance, Laramie, and Scollard Formations.[42]

Theropods

A theropod closely related to, and of overall similarity to, the feathered Asian genus Mononykus.

Theropod tracks have been found in South Dakota.[27] An unnamed alvarezsaurid, closely related to the Asian genus Mononykus, is known from Montana.[43] A second footprint that may have been made by a specimen of Tyrannosaurus was first reported in 2007 by British paleontologist Phil Manning, from the Hell Creek Formation of Montana. This second track measures 72 centimeters (28 in) long, shorter than the track described by Lockley and Hunt. Whether or not the track was made by Tyrannosaurus is unclear, though Tyrannosaurus is the only large theropod known to have existed in the Hell Creek Formation.[44][45]

Tyrannosaurids

Tyrannosaurids reported from the Hell Creek Formation
Genus Species Synonyms State Stratigraphic position Material Notes Images

Tyrannosaurus[8][26]

T. rex[8][26]

Lower to upper Hell Creek Formation.

A tyrannosaur, known from several specimens including a juvenile nicknamed "Jane". Also found in the Denver, Frenchman, Hill Creek South, Javelina, Lance, Ferris, Livingston, McRae, North Horn, Scollard, Willow Creek Formation, and also found in Lomas Coloradas Formations.

Ornithomimosaurs

Ornithomimid remains are not uncommon in the Hell Creek Formation.[8] Fifteen specimens from the Hell Creek Formation are undetermined ornithomimids[11]

Color key
Taxon Reclassified taxon Taxon falsely reported as present Dubious taxon or junior synonym Ichnotaxon Ootaxon Morphotaxon
Notes
Uncertain or tentative taxa are in small text; crossed out taxa are discredited.
Ornithomimids reported from the Hell Creek Formation
Genus Species State Stratigraphic position Material Notes Images

"Orcomimus"

unnamed

One partial skeleton.

An ornithomimid. Numem nudum

Struthiomimus[27]

S. sedens[47]

  • Montana
  • AMNH 975, a foot claw
  • UCMP 154569, a partial skeleton

A large ornithomimid similar to Gallimimus in size. Also found in the Lance Formation.[47]

Indeterminate ornithomimid

Indeterminate

  • Montana
  • South Dakota
  • North Dakota

Fragmentary specimens

Largely undescribed ornithomimid fossils originally classified as Ornithomimus velox, but later regarded as indeterminate.[48]

Oviraptorosaurs

Oviraptorosaur fossils have been found at the Hell Creek Formation for many years, most notably from isolated elements until the discovery of Anzu. In 1997, paleontologists discovered a fossil trackway of gigantic oviraptorid belonging to a creature dubbed Wakinyatanka styxi.[49]

Color key
Taxon Reclassified taxon Taxon falsely reported as present Dubious taxon or junior synonym Ichnotaxon Ootaxon Morphotaxon
Notes
Uncertain or tentative taxa are in small text; crossed out taxa are discredited.
Oviraptorosaurs reported from the Hell Creek Formation
Genus Species State Stratigraphic position Material Notes Images

Anzu[26][50]

A. wyliei[50]

Lower to upper Hell Creek Formation[11]

12 well-preserved specimens[10]

One of the largest known oviraptorosaurs, and the largest known from North America. Material previously assigned to Caenagnathidae indet. is now placed in the genus Anzu.[50]

Leptorhynchos

L. elegans

  • Montana

An extinct genus of caenagnathid.

File:Leptorhynchos elegans.jpg

Eumaniraptorans

Historically, numerous teeth have been attributed to various dromaeosaurid and troodontid taxa with known body fossils from only older formations, including Dromaeosaurus, Saurornitholestes, and Troodon. However, in a 2013 study, Evans et al. concluded that there is little evidence for more than a single dromaeosaurid taxon, Acheroraptor, in the Hell Creek-Lance assemblages, which would render these taxa invalid for this formation. This was disproved in a 2015 study, DePalma et al., when they described the new genus Dakotaraptor, a large species of dromaeosaur.[51] Though it should be noted as mentioned earlier that fossilized teeth of various troodontids and coelurosaurs are common throughout the Hell Creek Formation; the best known examples include Paronychodon, Pectinodon and Richardoestesia, respectively.

Eumaniraptorans reported from the Hell Creek Formation
Genus Species State Stratigraphic position Material Notes Images

Acheroraptor[51]

A. temertyorum [51]

Lower? to upper Hell Creek Formation[8]

  • ROM 63777, a maxilla and tooth[51]
  • ROM 63778, a partial dentary[51]
  • isolated teeth[51]

A velociraptorine dromaeosaurid. Teeth previously referred to various Campanian dromaeosaurids Saurornitholestes and Dromaeosaurus, frequently found throughout the formation, probably belong to this one species. Evans et al. conclude that there is little evidence for the former two taxa being present in the Hell Creek-Lance assemblages.[51]

Avisaurus[8]

A. archibaldi[8][26]

Middle Hell Creek Formation[10]

  • UCMP 117600, holotype, a tarsometatarsus
  • PU 17324, a tarsometatarsus

An avisaurid.[8]

cf. A. archibaldi[52]

Uppermost Hell Creek Formation[52]

  • YPM 57235, a coracoid

An avisaurid tentatively referred to A. archibaldi based on its size.[52]

A. sp.[53]

  • distal tarsals, metatarsus (juvenile)[53]

Brodavis[54]

B. baileyi[54]

  • UNSM 50665, a left tarsometatarsus missing proximal end, trochleae II and III.[54]

A primitive hesperornithiform.[54]

Dakotaraptor[55]

D. steini [55]

Upper Hell Creek Formation[55]

  • PBMNH.P.10.113.T, a partial skeleton.[55]
  • PBMNH.P.10.115.T, a tibia.[55]
  • PBMNH.P.10.118.T, an astragalocalcaneum.[55]
  • isolated teeth.[55]

A dromaeosaurid. Second-largest dromaeosaurid known.[51]

Potamornis[54]

P. skutchi [56]

  • UCMP 117605, a tarsometatarsus

A hesperornithiform also found in the Lance Formation.[56]

"Unnamed enantiornithine B"[52]

Unnamed

  • YPM 57823, a partial coracoid[52]

An unnamed enantiornithean.[52]

"Unnamed hesperornithiform A"[52]

Unnamed

  • Montana
  • UCMP 13355, a tarsometatarsus

A primitive hesperornithiform.[54] The Hell Creek specimen was referred to the same unnamed taxon as RSM P 2315.1 from the Canadian Frenchman Formation.[52] RSM P 2315.1 was later made the holotype of Brodavis americanus.[54] May be a synonym of Potamornis.[52]

"Unnamed ornithurine B"[52]

Unnamed[57]

  • UCMP 129143, a partial coracoid[52]

An ornithurine possibly similar to Cimolopteryx[52][57]

"Unnamed ornithurine C"[52]

Unnamed

  • SDSM 64281A, a partial coracoid[52]
  • SDSM 64281B, a partial coracoid[52]
  • UCMP 175251, a partial coracoid[52]
  • MOR 2918, a partial coracoid[52]

An ornithurine, also present in the Lance Formation and Fort Union Formation, one of the few individual bird species known to have survived the Cretaceous–Paleogene extinction[52]

"Unnamed ornithurine D"[52]

Unnamed

  • UCMP 187207, a partial coracoid[52]

An ichthyornithean also present in the Frenchman Formation[52]

Pterosaurs

Pterosaurs of the Hell Creek Formation
Taxa Species State Stratigraphic location Material Notes Images

Azhdarchidae spp.

Indeterminate

  • Montana[59]
  • North Dakota

Records of pterosaur remains from the Hell Creek Formation are two indeterminate specimens, which have been recorded from North Dakota but not described (Johnson et al., 2000; Pearson et al., 2002). A single azhdarchid neck bone may belong to the genus Quetzalcoatlus, though they are not diagnostic to the generic level.[59]

Crocodylomorphs

Color key
Taxon Reclassified taxon Taxon falsely reported as present Dubious taxon or junior synonym Ichnotaxon Ootaxon Morphotaxon
Notes
Uncertain or tentative taxa are in small text; crossed out taxa are discredited.
Crocodylomorphs reported from the Hell Creek Formation
Genus Species State Stratigraphic position Material Notes Images

Borealosuchus[60]

  • Montana
  • North Dakota
  • South Dakota

Extinct genus of crocodylians that lived from the Late Cretaceous to the Eocene in North America.

Brachychampsa[60]

  • Montana
  • South Dakota
  • North Dakota

Extinct genus of alligatoroid.

Thoracosaurus[60]

  • T. neocesariensis[60]
  • Montana

Extinct genus of gavialoid crocodilian which existed during the Late Cretaceous and early Paleocene.

Turtles

Color key
Taxon Reclassified taxon Taxon falsely reported as present Dubious taxon or junior synonym Ichnotaxon Ootaxon Morphotaxon
Notes
Uncertain or tentative taxa are in small text; crossed out taxa are discredited.
Turtles reported from the Hell Creek Formation
Genus Species State Stratigraphic position Material Notes Images

Adocus[61]

Indeterminate[61]

Extinct genus of aquatic turtles belonging to the family Adocidae.

Axestemys[63]

A. splendida

  • North Dakota
  • South Dakota

Trionychidae turtle.

Compsemys[61]

C. victa[61]

A relative of Dermatemydidae.

Peckemys

P. brinkman

  • Montana
  • North Dakota

A relative of Baenidae.

Emarginachelys

E. cretacea

  • Montana

A relative of chelydrids.[64]

Eubaena[61]

E. cephalica[61]

Baenid turtle

Gamerabaena

G. sonsalla

  • North Dakota

Extinct genus of baenid turtle.

Palatobaena

P. cohen

  • North Dakota

A relative of extinct family of cryptodiran turtles.

Cedrobaena

C. putorius

  • South Dakota
  • North Dakota

A relative of Baenidae.

Gilmoremys

G. lancensis

  • Montana
  • North Dakota

Trionychidae related to the softshell turtle.

Hoplochelys[64]

H. clark[64]

A kinosternoid related to the Central American river turtle.[64]

Plastomenus

P. sp

Trionychidae turtle.

Basilemys

B. sinuosa

Largest dermatemydid land tortoise.

Trionyx[61]

Indeterminate[61]

A genus of softshell turtles belonging to the family Trionychidae.

Aspideretoides

A. foveatus

Trionychidae turtle.

Helopanoplia

H. distincta

Trionychidae turtle.

Clemmys

C. backmani

Thin-shelled macrobaenid turtle.

Plesiobaena

P. antiqua

Baenid turtle.

Stygiochelys

S. estesi

Baenid turtle.

Neurankylus

N. eximius

Largest baenid turtle in Hell Creek Formation.

Thescelus

T. insiliens

Baenid turtle.

Chelydridae

Indeterminate

Chelydrids-like turtle.

Lizards and snakes

Color key
Taxon Reclassified taxon Taxon falsely reported as present Dubious taxon or junior synonym Ichnotaxon Ootaxon Morphotaxon
Notes
Uncertain or tentative taxa are in small text; crossed out taxa are discredited.
squamates reported from the Hell Creek Formation
Genus Species State Stratigraphic position Material Notes Images

Cemeterius[65][66]

C. monstrosus[65][66]

A platynotan lizard of uncertain phylogenetic placement, also known from the Lance Formation.[65]

Cerberophis[65][66]

C. robustus[65][66]

An alethinophidian snake of uncertain phylogenetic placement.[65]

Obamadon[65][66]

O. gracilis[65][66]

A polyglyphanodontian lizard of uncertain phylogenetic placement. Also known from the Lance Formation.[65]

Peneteius[65]

P. aquilonius[65]

A chamopsiid polyglyphanodontian lizard.[65]

Haptosphenus

H. placodon

Teiidae lizard.

Leptochamops

L. denticulatus

Small Teiidae lizard.

Chamops

C. segnis

Largest Teiidae lizard in Hell Creek Formation

Contogenys

C. sloani

Scincidae? lizard.

Exostinus

E. lancensis

xenosaurid lizard.

Proxestops

P. jepseni

Anguidae lizard.

Parasaniwa

P. wyomingensis

Necrosaurid lizard.

Paraderma

P. bogerti

Helodermatidae? lizard.

Palaeosaniwa

P. canadensis

A large Monstersauria lizard, closely related to today's varanid lizards. It was the largest lizard in the Hell Creek formation.

Boidae

Indeterminate

Snake. Earliest-known boid.

Choristoderans

Color key
Taxon Reclassified taxon Taxon falsely reported as present Dubious taxon or junior synonym Ichnotaxon Ootaxon Morphotaxon
Notes
Uncertain or tentative taxa are in small text; crossed out taxa are discredited.
Choristoderans reported from the Hell Creek Formation
Genus Species State Stratigraphic position Material Notes Images

Champsosaurus[60]

C. sp.[60]

  • Montana

A champsosaur.

Mammals

Multituberculates

Color key
Taxon Reclassified taxon Taxon falsely reported as present Dubious taxon or junior synonym Ichnotaxon Ootaxon Morphotaxon
Notes
Uncertain or tentative taxa are in small text; crossed out taxa are discredited.
Multituberculates reported from the Hell Creek Formation
Genus Species State Stratigraphic position Material Notes Images

Cimexomys[67]

C. minor[67]

A multituberculate of uncertain phylogenetic placement.

Cimolodon[67]

C. nitidus

  • Montana
  • North Dakota[67]

A cimolodontid multituberculate.

C. cf. nitidus[67]

A cimolodontid multituberculate.

C. sp.[67]

A cimolodontid multituberculate.

Cimolomys[67]

C. gracilis

A cimolodontid multituberculate.

A cimolomyid multituberculate.

Essonodon[67]

E. browni[67]

A cimolomyid multituberculate.

Meniscoessus[67]

M. conquistus

A cimolomyid multituberculate.

M. robustus

  • Montana
  • North Dakota
  • South Dakota[67]

A cimolomyid multituberculate.

M. cf. robustus

A cimolomyid multituberculate.

M. sp.

A cimolomyid multituberculate.

?M. sp.[67]

A cimolomyid multituberculate.

Mesodma[67]

M. formosa

  • Montana
  • South Dakota[67]

A neoplagiaulacid multituberculate.

M. cf. formosa

A neoplagiaulacid multituberculate.

M. hensleighi

  • Montana
  • South Dakota[67]

A neoplagiaulacid multituberculate.

M. cf. hensleighi

A neoplagiaulacid multituberculate.

M. thompsoni

  • Montana
  • North Dakota
  • South Dakota[67]

A neoplagiaulacid multituberculate.

M. cf. thompsoni

A neoplagiaulacid multituberculate.

M sp.[67]

A neoplagiaulacid multituberculate.

?M sp.[67]

A neoplagiaulacid multituberculate.

?Neoplagiaulax[67]

?N. burgessi[67]

A neoplagiaulacid multituberculate.

Paracimexomys[67]

P. priscus[67]

A multituberculate of uncertain phylogenetic placement.

Paressonodon[68]

P. nelsoni[68]

A cimolomyid multituberculate.

Stygimys

S. kuszmauli

  • Montana

It was a member of the extinct order Multituberculata.

Metatherians

Color key
Taxon Reclassified taxon Taxon falsely reported as present Dubious taxon or junior synonym Ichnotaxon Ootaxon Morphotaxon
Notes
Uncertain or tentative taxa are in small text; crossed out taxa are discredited.
Metatherians reported from the Hell Creek Formation
Genus Species State Stratigraphic position Material Notes Images

Aletridelphys[69][70]

A. florencae

  • Montana
  • North Dakota
  • South Dakota[67]

A pediomyid.

A. hatcheri[69]

  • Montana
  • South Dakota[67]

A pediomyid.

Alphadon[67]

A. marshi

  • Montana
  • North Dakota[67]

An alphadontid. genus of small, primitive mammal that was a member of the Metatheria, a group of mammals that includes modern-day marsupials.

A. cf. marshi

  • Montana
  • South Dakota[67]

An alphadontid.

A. wilsoni

An alphadontid.

A. cf. wilsoni

An alphadontid.

A. sp.[67]

  • North Dakota
  • South Dakota[67]

An alphadontid.

Didelphodon[67]

D. padanicus

A stagodontid.

D. vorax

  • Montana
  • North Dakota[67]

A stagodontid. genus of Stagodontidae marsupials from the Late Cretaceous of North America.

D. cf. vorax

A stagodontid.

D. sp.

A stagodontid.

cf. D. sp.[67]

  • North Dakota
  • South Dakota[67]

A stagodontid.

Glasbius[67]

G. twitchelli

A glasbiid.

G. cf. twitchelli[67]

A glasbiid.

Leptalestes[69]

L. cooki

A pediomyid.

L. krejcii[69]

  • Montana
  • South Dakota[67]

A pediomyid.

Nanocuris[68]

N. improvida[68]

A deltatheridiid.

Nortedelphys

N. jasoni (= N. intermedius)[68][71]

  • Montana
  • South Dakota

A herpetotheriid.

Pediomys[67]

P. elegans[67]

  • Montana
  • South Dakota[67]

A pediomyid.

Protalphadon[67]

P. foxi

An alphadontid.

P. lulli[67]

An alphadontid.

Turgidodon[67]

T. rhaister[67]

An alphadontid.

Eutherians

Color key
Taxon Reclassified taxon Taxon falsely reported as present Dubious taxon or junior synonym Ichnotaxon Ootaxon Morphotaxon
Notes
Uncertain or tentative taxa are in small text; crossed out taxa are discredited.
Eutherians reported from the Hell Creek Formation
Genus Species State Stratigraphic position Material Notes Images

Altacreodus

A. magnus

  • Montana
  • North Dakota

a possibe creodont, formally a species of Cimolestes[72]

Ambilestes

A. cerberoides

  • Montana

A eutherian of uncertain classification, formally a species of Cimolestes

Alostera[67]

A. saskatchewanensis[67]

A eutherian of uncertain phylogenetic placement.

Batodon[67]

B. tenuis[67]

A cimolestid eutherian.

Cimolestes[67]

C. incisus

A cimolestid eutherian.

C. stirtoni[67]

A cimolestid eutherian.

Gypsonictops[67]

G. hypoconus

  • Montana
  • South Dakota[67]

A gypsonictopsid eutherian.

G. illuminatus

  • Montana
  • North Dakota[67]

A gypsonictopsid eutherian.

G. cf. illuminatus

A gypsonictopsid eutherian.

G. sp.[67]

A gypsonictopsid eutherian.

cf. Paranyctoides[67]

cf. Paranyctoides sp.[67]

A nyctitheriid eutherian.

Protungulatum[69]

P. coombsi[69]

A stem-placental.

Purgatorius

P. ceratops

  • Montana

A genus with four species believed to be either stem-placentals or stem-primates.

Scollardius

S. propalaeoryctes

  • Montana

A eutherian of uncertain classification, formally a species of Cimolestes

Plants

Although the first representatives of leafy trees and true grasses emerged in the Cretaceous, the flora was still dominated by conifers like Araucaria.

The Hell Creek Formation was a low floodplain at the time before the sea retreated, and in the wet ground of the dense woodland, laurels, sycamores, beech, magnolias, and palm trees grew. Ferns and moss grew in the forest understory. Plant fossils from the upper early Paleocene of the Hell Creek Formation include the ferns Botrychium, Woodwardia, Osmunda, Onoclea and Azolla; Conifers Metasequoia, Cupressaceous conifers and Glyptostrobus; the monocot Limnobiophyllum (a relative of duckweeds); and the dicots Cercidiphyllum and Platanus.[73][74] There are numerous types of leaves, seeds, flowers and other structures from Angiosperms, or flowering plants. The Hell Creek Formation of this layer contains 300 tablets or more of plants. Angiosperms are by far the most diverse and dominant flora of the entire population, about 90 percent. However, the evergreens included conifers, ginkgo, bald cypress, and cycads. Flowering plants included a variety of trees that no longer exist. Today Hell Creek's flora is hardwood forest mixed with deciduous and evergreen forest and apparently similar to then, but with a closer look, the current plant community is distinct. In sharp contrast to Montana today, the presence of palm trees meant the climate was warmer then.

Fossil fruits from the Hell Creek Formation of Spinifructus antiquus of the palm family (Arecaceae), closely related to the genus Astrocaryum.

Dr. Kirk Johnson (Scientist) claims that there are no grasses, oaks, maples, or willows in the Hell Creek Formation. Ferns are uncommon in the majority of the formation, however there is a great increase in the abundance of fossil fern spores in the two centimeters of rock that directly overlies the impact fallout layer (the famous K-T boundary layer). This increase in fern spore abundance is commonly referred to as "the fern spike" (meaning that if the abundance of spores as a function of stratigraphic position were plotted out, the graph would show a spike just above the impact fallout layer). Johnson also found that the majority of the angiosperm genera in the Hell Creek Formation are now extinct. He also believes that, very roughly, 80% of the terrestrial plant taxa died out in what is now Montana and the Dakotas at the K/T boundary.

Many of the modern plant affinities in the Hell Creek Formation (e.g., those with the prefix "aff." or with quotes around the genus name) may not in reality belong to these genera; instead they could be entirely different plants that resemble modern genera. Therefore, there is some question regarding whether the modern Populus or Juglans, as two examples, actually lived in the late Cretaceous.

Compared to the rich Hell Creek Formation fossil plant localities of the Dakotas, relatively few plant specimens have been collected from Montana. A few taxa were collected at Brownie Butte Montana by Shoemaker, but most plants were collected from North Dakota (Slope County) and from South Dakota. "TYPE" after the binomial means that it is represented by a type specimen found in the Yale-Peabody Museum collections. "YPM" is the prefix for the Yale-Peabody Museum specimen number.

Overview (from Johnson, 1997): 190 plant morphotypes, including:

  • 1 bryophyte (mosses and liverworts)
  • 6 "pteridophytes" (A paraphyletic group: modern examples are horsetails, club mosses and ferns.)
  • 9 conifers
  • 2 ginkgo (uncommon)
  • 172 angiosperms (90% of all specimens collected, as well as 90% of all taxa found)
Plants of the Hell Creek Formation

Gymnosperms

Ginkgos

Angiosperms

Color key
Taxon Reclassified taxon Taxon falsely reported as present Dubious taxon or junior synonym Ichnotaxon Ootaxon Morphotaxon
Notes
Uncertain or tentative taxa are in small text; crossed out taxa are discredited.
Flora of the Hell Creek Formation
Genus Species Location Stratigraphic position Abundance Notes Images

Aquilapollenites

"Aquilapollenites" attenuatus

"Aquilapollenites" collaris

"Aquilapollenites" conatus

"Aquilapollenites" delicatus

"Aquilapollenites" marmarthensis

"Aquilapollenites" quadricretaeus

"Aquilapollenites" quadrilobus

"Aquilapollenites" reductus

"Aquilapollenites" senonicus

"Aquilapollenites" turbidus

"Aquilapollenites" striatus

Alnipollenites

"Ficus"

"Ficus" planicostata

"Ficus" artocarpoides

"Ficus" trinervis

Ilexpollenites

Ilexpollenites compactus

Interpollis

Interpollis cf. I. supplingensis

Balmeisporites

Balmeisporites sp.

Marmarthia

Marmarthia pearsonii

"Myrica"

"Myrica" torreyi

Platanites

Platanites marginata

Sabalites

Sabalites sp.

Tricolpites

Tricolpites interangulus

Metasequoia

M. sp

Casts of Dawn Redwood seed cones are known from the Hell Creek.

"Grewiopsis"

"G" saportana

Another generic Hamamelididae.

Annona?

A?. robusta

Abundant at Brownie Butte, Montana.

Cobbania

C. corrugata

A prehistoric species of water lettuce, previously assigned to the genus Pistia.

Araucaria

A. araucana

Casts of Monkey-puzzle leaves are found in Hell Creek.

Artocarpus

A. lessigiana

Abundant at Brownie Butte, Montana.

Celastrus

C. taurenensis

Some may be Eucommiacaea.

Cinnamomum

C. lineafolia

Included in Ficus affinis by L. Hickey. Belongs in Rhamnaceae (modern buckthorns and Ceanothus). Some other specimens referred to Cinnamomum sezanensis(?) sp.), a real cinnamon bush.

Cissu

C. marginata

Also spelled "marginatus".

Juglans

J. leconteana

Liriodendrites

L. bradacci

Johnson, 1996. In the Magnoliidae: a common taxon.

Liriodendron

L. laramiense

May be related to today's tulip tree (yellow poplar).

Leepiesceia

L. presrtocarpoides

another laurel.

Marmarthia

M. pearsonii

Johnson, 1996. In the Lauraceae: a common taxon.

M. trivialis

Johnson, 1996. In the Lauraceae: a common taxon.

Platanites

P. marginata

Johnson, 1996. In the Platanaceae: Hamamelididae. A common taxon.

Quercus

Q. viburnifolia

Included within "Cissus" marginata. May be in the Platanaceae.

Dombeyopsis

D. trivialis

Included within "Cissus" marginata. May be in the Platanaceae.

D. obtusa

Included within "Cissus" marginata. May be in the Platanaceae.

Rhamnus

R. cleburnii

A buckthorn look-alike.

Vitis

V. stantonii

This could be a real Vitus (a real grape).

Ziziphus

Z. fibrillosus

Androvettia

A. catenulata

Araliaephyllum

A. polevoi

Bisonia

B. niemii

Incertae sedis. Johnson, 1996. A broad leaf, probably in the Laurales. A common taxon. Type specimen was found near a Tyrannosaurus skeleton in South Dakota.

Cannabaceae

C. sp

Cissites

C. insignis

May belong in Hamemelididae.

C. lobata

C. puilasokensis

Cupressinocladus

C. interruptus

Dombeyopsis

D. trivialis

Elatides

E. longifolia

In Platanales, according to Leo Hickey.

Erlingdorfia

E. montana

Johnson, 1996. In the Platanaceae: Hamamelididae (related to today's Sycamore). A common taxon.

Ginkgo

G. adiantoides

The only ginkgo in the Hell Creek Formation; uncommon

Glyptostrobus

G. nordenskioldii

G. sp

Laurophyllum

L. wardiana

Magnolia

M. pulchra

This species was thought to occur only in southern Wyoming flora, but Leo Hickey claims it is found further north in Montana and the Dakotas.

Marchantia

M. pealii

Nilssonia

N. yukonensis

The only Hell Creek Formation cycadeoid. Uncommon.

Onoclea

O. hesperia

Paranymphaea

P. hastata

Platanophyllum

P. montanum

Porosia

P. verrucosa

Rhamnus

R. salicifolius

Another buckthorn look-alike. Abundant at Brownie Butte, Montana

Sabalites

S. sp

Palm tree.

Sapindopsis

S. powelliana

Sequoites

S. artus

Sequoia tree.

Taxodium

T. olrikii

Related to today's bald cypress.

Trochodendroides

T. arctica

T. nebrascensis

Zingiberopsis

Z. attenuata

Related to today's ginger plant. Its closest living relative is the Asian genus Alpinia. Some Hell Creek Formation specimens show damage from hispine beetles ("leaf beetles" (Wilf et al., 2000)).

Dryophyllum

D. subfalcatum

One of the most common plant taxa in the Hell Creek and Lance Formations. Common at Brownie Butte, Montana. If it is close to real Dryophyllum, then it is a beech/chestnut-like tree (Fagaceae). It may also be a walnut-like tree (Juglandaceae).

D. tenneseensis

see above.

aff. "Dryophyllum" subfalcatum

see above.

Populus

P. nebrascensis

Cocculus

cf. C. flabella

Cissites

cf. C. acerifolia

Pistia

cf. P. corrugata

Floating aquatic herb.

Palaeoaster

P. inquirenda

A poppy with quite similar seed pods and seeds to that of the extant poppy genus Romneya.

See also

References

  1. ^ http://faculty.washington.edu/gpwilson/wordpress/hell-creek-project/
  2. ^ Husson, D., Galbrun, B., Laskar, J., Hinnov, L. A., Thibault, N., Gardin, S., & Locklair, R. E. (2011). "Astronomical calibration of the Maastrichtian (late Cretaceous)". Earth and Planetary Science Letters. 305 (3): 328–340. Bibcode:2011E&PSL.305..328H. doi:10.1016/j.epsl.2011.03.008.{{cite journal}}: CS1 maint: multiple names: authors list (link)
  3. ^ a b Pearson, D. A., Schaefer, T., Johnson, K. R., Nichols, D. J., & Hunter, J. P. (2002). Vertebrate biostratigraphy of the Hell Creek Formation in southwestern North Dakota and northwestern South Dakota. Hartman et al, 145-167.
  4. ^ Johnson, K. R., Nichols, D. J., & Hartman, J. H. (2002). Hell Creek Formation: A 2001 synthesis. The Hell Creek Formation and the Cretaceous-Tertiary Boundary in the northern Great Plains: Geological Society of America Special Paper, 361, 503-510.
  5. ^ Lofgren, D.F. (1997). "Hell Creek Formation". In: The Encyclopedia of Dinosaurs. San Diego: Academic Press. 1997. pp. 302–303. ISBN 978-0-122-26810-6. {{cite book}}: Unknown parameter |authors= ignored (help)
  6. ^ Breithaupt, B.H. (1997). "Lance Formation". In: The Encyclopedia of Dinosaurs. San Diego: Academic Press. 1997. pp. 394–395. ISBN 978-0-122-26810-6. {{cite book}}: Unknown parameter |authors= ignored (help)
  7. ^ Eberth, D.A. (1997). "Edmonton Group". In: The Encyclopedia of Dinosaurs. San Diego: Academic Press. 1997. pp. 199–204. ISBN 978-0-122-26810-6. {{cite book}}: Unknown parameter |authors= ignored (help)
  8. ^ a b c d e f g h i j k l m n o p q r s t u v w x y z aa ab ac ad ae af ag ah ai aj ak al am an ao ap aq ar as at au av aw ax Pearson et al. (2002) p. 154
  9. ^ a b c d e f g h i j k l m n o p q r s t u v w x y z aa ab ac ad ae af ag ah ai aj Pearson et al. (2002) pp. 145–167
  10. ^ a b c d e f g h i j k l m n o p q r s Pearson et al. (2002) p. 155
  11. ^ a b c d e f g h i j k l m n o p q r s Pearson et al. (2002) pp. 156
  12. ^ Listed as "cf. Barbourula sp." in "Class Amphibia," Estes and Berberian, (1970). Page 4.
  13. ^ a b c d e f g h i j k l m n o p "Class Amphibia," in Estes and Berberian, (1970). Page 4.
  14. ^ a b c d e f g h i "Class Amphibia," in Estes and Berberian, (1970). Page 4. All taxa listed occur in Montana, see page 1.
  15. ^ Listed as "Eopelobates? sp." in "Class Amphibia," Estes and Berberian, (1970). Page 4.
  16. ^ a b c d David G. Demar Jr. (2013). "A new fossil salamander (Caudata, Proteidae) from the Upper Cretaceous (Maastrichtian) Hell Creek Formation, Montana, U.S.A.". Journal of Vertebrate Paleontology. 33 (3): 588–598. doi:10.1080/02724634.2013.734887.
  17. ^ a b c d e f g h i j k l m n o p "Class Osteichthyes," in Estes and Berberian, (1970). Page 3.
  18. ^ a b c d e f g h "Class Osteichthyes," in Estes and Berberian, (1970). Page 3. All taxa listed occur in Montana, see page 1.
  19. ^ a b c d "Class Osteichthyes," in Estes and Berberian, (1970). Page 4.
  20. ^ a b c "Class Osteichthyes," in Estes and Berberian, (1970). Page 4. All taxa listed occur in Montana, see page 1.
  21. ^ a b Listed as "cf. Paralbula casei" in "Class Osteichthyes," Estes and Berberian, (1970). Page 4.
  22. ^ a b c d e f g h i j k l m n o p q r s Todd D. Cook; Michael G. Newbrey; Donald B. Brinkman; James I. Kirkland (2014). "Euselachians from the freshwater deposits of the Hell Creek Formation of Montana". GSA Special Papers. 503: 229–246. doi:10.1130/2014.2503(08).
  23. ^ a b "Class Chondrichthyes," in Estes and Berberian, (1970). Page 3.
  24. ^ "Class Chondrichthyes," in Estes and Berberian, (1970). Page 3. All taxa listed occur in Montana, see page 1.
  25. ^ Manning, P. L.; Ott, C.; Falkingham, P. L. (2008). "The first tyrannosaurid track from the Hell Creek Formation (Late Cretaceous), Montana, U.S.A.". PALAIOS. 23: 645–647. Bibcode:2008Palai..23..645M. doi:10.2110/palo.2008.p08-030r.
  26. ^ a b c d e f g h i j k l m n o p q r s t u v w x y z aa ab ac ad ae af ag ah ai aj "Dinosaur distribution (Late Cretaceous; North America; Montana)." Weishampel, et al. (2004). Page 584.
  27. ^ a b c d e f g h i j k "Dinosaur distribution (Late Cretaceous; North America; South Dakota)." Weishampel, et al. (2004). Page 586.
  28. ^ a b c d "Dinosaur distribution (Late Cretaceous; North America; North Dakota)." Weishampel, et al. (2004). Page 585.
  29. ^ a b c d Bakker et al. (2006)
  30. ^ "Table 21.1," in Weishampel, et al. (2004). Page 465.
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  32. ^ "Super-sized Ceratopsian Skull Might be New Species". Everything Dinosaur. Retrieved 29 August 2015.
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  38. ^ Jasinski, Steven E.; Sullivan, Robert M.; Lucas, Spencer G.; Spielmann, Justin A. "The first "lambeosaurin" (Dinosauria, Hadrosauridae, Lambeosaurinae) from the Upper Cretaceous Ojo Alamo Formation (Naashoibito Member), San Juan Basin, New Mexico: further implications for the age of the Alamo Wash local fauna". www.researchgate.com. ResearchGate. Retrieved 23 September 2016.
  39. ^ a b Campione, N.E.; Evans, D.C. (2011). "Cranial Growth and Variation in Edmontosaurs (Dinosauria: Hadrosauridae): Implications for Latest Cretaceous Megaherbivore Diversity in North America". PLoS ONE. 6 (9): e25186. Bibcode:2011PLoSO...625186C. doi:10.1371/journal.pone.0025186. PMC 3182183. PMID 21969872.{{cite journal}}: CS1 maint: unflagged free DOI (link)
  40. ^ a b Listed as "?Thescelosaurus garbanii" in "Dinosaur distribution (Late Cretaceous; North America; Montana)." Weishampel, et al. (2004). Page 584.
  41. ^ Noted as being present, although misspelled as "Thescelosaurus garbani, in " "Dinosaur distribution (Late Cretaceous; North America; South Dakota)." Weishampel, et al. (2004). Page 586.
  42. ^ Boyd, Brown, et al. (2009)
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  44. ^ Dalman, S.G.; Lucas, S.G. "A new large Tyrannosaurid Alamotyrannus brinkmani, n. gen., n. sp. (Theropoda: Tyrannosauridae), from the Upper Cretaceous Ojo Alamo Formation (Naashoibito Member), San Juan Basin, New Mexico". New Mexico Museum of Natural History and Science Bulletin. In Press. {{cite journal}}: |access-date= requires |url= (help)
  45. ^ Molnar, R. E. (January). "An Albertosaur from the Hell Creek Formation of Montana". Journal of Paleontology. 54 (1): 102–108. {{cite journal}}: Check date values in: |date= (help)
  46. ^ Triebold, 1997. The Sandy Site: Small Dinosaurs from the Hell Creek Formation of South Dakota. in Wolberg, Stump and Rosenberg (eds). Dinofest International: Proceedings of a Symposium sponsored by Arizona
  47. ^ a b Longrich (2008), pages 983-996.
  48. ^ Russell, D (1972). "Ostrich dinosaurs from the Late Cretaceous of western Canada". Canadian Journal of Earth Sciences. 9 (4): 375–402. Bibcode:1972CaJES...9..375R. doi:10.1139/e72-031.
  49. ^ Maltese, Anthony. "Giant Oviraptor Tracks from the Hell Creek". RMDRC paleo lab. Retrieved 17 December 2013.
  50. ^ a b c d e Lamanna, M. C.; Sues, H. D.; Schachner, E. R.; Lyson, T. R. (2014). "A New Large-Bodied Oviraptorosaurian Theropod Dinosaur from the Latest Cretaceous of Western North America". PLoS ONE. 9 (3): e92022. Bibcode:2014PLoSO...992022L. doi:10.1371/journal.pone.0092022. PMC 3960162. PMID 24647078.{{cite journal}}: CS1 maint: unflagged free DOI (link)
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Bibliography

  • Pearson, D.A.; Schaefer, T.; Johnson, K.R.; Nichols, D.J.; Hunter, J.P. (2002). Hartman, John H.; Johnson, Kirk R.; Nichols, Douglas J. (eds.). "Vertebrate Biostratigraphy of the Hell Creek Formation in Southwestern North Dakota and Northwestern South Dakota". Geological Society of America Special Paper 361. The Hell Creek Formation and the Cretaceous-Tertiary boundary in the northern Great Plains: An integrated continental record of the end of the Cretaceous. Boulder, Colorado: 145–167.
  • Bakker, R. T., Sullivan, R. M., Porter, V., Larson, P. and Saulsbury, S.J. (2006). "Dracorex hogwartsia, n. gen., n. sp., a spiked, flat-headed pachycephalosaurid dinosaur from the Upper Cretaceous Hell Creek Formation of South Dakota." in Lucas, S. G. and Sullivan, R. M., eds., Late Cretaceous vertebrates from the Western Interior. New Mexico Museum of Natural History and Science Bulletin 35, pp. 331–345. [1]
  • Boyd, Clint A.; Brown, Caleb M.; Scheetz, Rodney D.; Clarke; Julia A. (2009). "Taxonomic revision of the basal neornithischian taxa Thescelosaurus and Bugenasaura". Journal of Vertebrate Paleontology. 29 (3): 758–770. doi:10.1671/039.029.0328.
  • Estes, R., and P. Berberian. 1970. Paleoecology of a late Cretaceous vertebrate community from Montana. Breviora volume 343, 35 pages.
  • Henderson, M.D.; Peterson, J.E. (2006). "An azhdarchid pterosaur cervical vertebra from the Hell Creek Formation (Maastrichtian) of southeastern Montana". Journal of Vertebrate Paleontology. 26 (1): 192–195. doi:10.1671/0272-4634(2006)26[192:aapcvf]2.0.co;2.
  • Longrich, N (2008). "A new, large ornithomimid from the Cretaceous Dinosaur Park Formation of Alberta, Canada: Implications for the study of dissociated dinosaur remains". Palaeontology. 54 (1): 983–996.
  • Varricchio, D. J. 2001. Late Cretaceous oviraptorosaur (Theropoda) dinosaurs from Montana. pp. 42–57 in D. H. Tanke and K. Carpenter (eds.), Mesozoic Vertebrate Life. Indiana University Press, Indianapolis, Indiana.
  • Weishampel, David B.; Dodson, Peter; and Osmólska, Halszka (eds.): The Dinosauria, 2nd, Berkeley: University of California Press. 861 pp. ISBN 0-520-24209-2.
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