Hell Creek Formation

Hell Creek Formation Stratigraphic range: Maastrichtian–Danian, 66.8–66 Ma PreЄ Є O S D C P T J K Pg N ↓
Exposure in the badlands in the vicinity of Fort Peck Reservoir
Type	Geological formation
Underlies	Fort Union Formation
Overlies	Fox Hills Formation
Location
Region	Montana   North Dakota  South Dakota  Wyoming

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. "Pompey's Pillar" at the 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 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.^[1] Fauna characteristic of the Hell Creek (Lancian land vertebrate age) are found as high as a few meters below the boundary.^[2]

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.^[2] 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.^[3]

Paleobiota

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, Caenagnathidae, a variety of small theropods, Pachycephalosaurs, Crocodylomorphs, and Squamates, including various animal fossils unearthed in the Hell Creek Formation. The most complete Hadrosaurid dinosaur ever found was retrieved in 2000 from the Hell Creek Formation and widely publicised 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.

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.^[4][5][6] 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)[7]	indeterminate[7]	North Dakota[8] South Dakota[8]	Middle to upper Hell Creek Formation[9]	3 unassigned specimens[10]	Anura indet. consists of material not currently assigned to any genus of frog.[7]
Barbourula[11]	Indeterminate[12]	Montana[13]
Caudata (salamander)[7]	indeterminate[7]	North Dakota[8] South Dakota[8]	Lower to uppermost Hell Creek Formation[9]	149 unassigned specimens[10]	Material of Caudata indet. is not currently assigned to any genus.[7]
Eopelobates[14]	Indeterminate[12]	Montana[13]
Habrosaurus[7][12]	H. dilatus[7][12]	Montana[13] North Dakota[8] South Dakota[8]	Middle to upper Hell Creek Formation[9]	6 specimens[10]	Habrosaurus is a sirenid amphibian.[7]
Lisserpeton[12]	L. bairdi[12]	Montana[13]
Opisthotriton[7][12]	O. kayi[7][12]	Montana[13] North Dakota[8] South Dakota[8]	Lower to upper Hell Creek Formation[9]	22 specimens[10]	Opisthotriton is classified as a Batrachosauroididae.[7]
Paranecturus[15]	P. garbanii[15]	Montana[15]			A member of Proteidae.[15]
Proamphiuma[12]	P. cretacica[12]	Montana[13]
Prodesmodon[12]	P. copei[12]	Montana[13]
Scapherpeton[7][12]	S. tectum[7][12]	Montana[13] North Dakota[8] South Dakota[8]	Lower to upper Hell Creek Formation[9]	144 specimens[10]	Scapherpeton is a scapherpetonid that is very common in the Hell Creek Formation.[7]
Scotiophryne[12]	S. pustulosa[12]	Montana[13]			A small frog

Fishes

Bony fishes

Bony fishes reported from the Hell Creek Formation
Genus	Species	Location	Stratigraphic position	Material	Notes	Images
Acipenser[7][16]	A. eruciferus[16]	Montana[17]			A sturgeon
	cf. A. sp.[7]	North Dakota[8] South Dakota[8]	Lower to upper Hell Creek Formation[9]	18 specimens are tentatively assigned to Acipenser sp.[10]	Acipenser sp. is tentatively referred to the genus.[7]
Amia[16]	A. fragosa[16]	Montana[17]			small amiid fish (ubiquitous). Closely related to the modern Bowfin
Belonostomus[7][16]	B. longirostris[7][16]	Montana[17] North Dakota[8] South Dakota[8]	Lower to upper Hell Creek Formation[9]	28 specimens[10]	A long-snouted slender fish classified as an aspidorhynchid.[7]
Coriops[18]	C. amnicolus[18]	Montana[19]
Kindleia[7]	K. fragosa[7]	North Dakota[8] South Dakota[8]	Lower to uppermost Hell Creek Formation[9]	2610 specimens have been assigned to Kindleia, making it an extremely common genus.[10]	Kindleia is a genus assigned to Amiidae, along with Melvius and Amia.[7]
Lepisosteus[7][16]	L. occidentalis[7][16]	Montana[17] North Dakota[8] South Dakota[8]	Lower to uppermost Hell Creek Formation[9]	938 specimens are assigned to Lepidosteus[10]	A lepidosteid that is very common in the Hell Creek Formation.[7]
Melvius[7]	M. thomasi[7]	North Dakota[8] South Dakota[8]	Lower to upper Hell Creek Formation[9]	6 specimens are assigned to Melvius[10]	A large amiid fish.[7]
Phyllodus	P. paulkatoi				fish with columnar teeth
Palaeolabrus[16]	P. montanensis[16]	Montana[17]
Paleopsephurus[16]	P. wilsoni[16]	Montana[17]			A paddlefish
Palaeolabrus	P. montanensis				fish (incertae sedis)
Paralbula[20]	P. casei[20]	Montana[19]
Platacodon[18]	P. nanus[18]	Montana[19]			small teleost fish
Protamia[16]	Indeterminate[16]	Montana[17]
Pachyrhizodontoidei	Indeterminate				Fish
Protoscaphirhynchus[16]	P. squamosus[16]	Montana[17]			a sturgeon

Cartilaginous fishes

Chondrichthyes reported from the Hell Creek Formation
Genus	Species	Location	Stratigraphic position	Material	Notes	Images
Chiloscyllium[21]	C. sp.[21]	Montana[21]			A member of Hemiscylliidae.[21]
Lonchidion[22]	L. selachos[22]	Montana[23] North Dakota[8] South Dakota[8]	Lower to upper Hell Creek Formation[9]	40 specimens[10]	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.[7]
Myledaphus[21]	M. pustulosus[21]	Montana[21] North Dakota[8] South Dakota[8]	Lower to upper Hell Creek Formation.[9]	1677 specimens[10] previously assigned to M. bipartitus.[21]	Is an anacoracid batoid[7] rajiform related to guitarfishes.[21] Described on the basis of teeth formerly assigned to the species M. bipartitus.[21] The material assigned to Myledaphus bipartitus and makes up 16.5% of the vertebrate remains.[7]
Protoginglymostoma[21]	P. estesi[21]	Montana[21]			A member of Ginglymostomatidae.[21] Formerly assigned to the genus Brachaelurus.
Restesia[21]	R. americana[21]	Montana[21] North Dakota[8] South Dakota[8]	Middle Hell Creek Formation[9]	5 specimens previously assigned to Squatirhina[10]	A wobbegong-like shark.[21] Formerly assigned to Squatirhina. The remains consist of 0.05% of the vertebrates.[10] Also known from the Lance Formation.[21]

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).

• Ceratopsidae 61%
• Hadrosauridae 23%
• Ornithomimidae 5%
• Tyrannosauridae 4%
• Hypsilophodontidae 3%
• Dromaeosauridae 2% (represented only by teeth)
• 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. Small predatory dinosaurs, such as 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.

Ornithischians

Ankylosaurs

Ankylosauria reported from the Hell Creek Formation
Genus	Species	State	Stratigraphic position	Material	Notes	Images
Ankylosaurus[24]	Ankylosaurus magniventris[24]	Montana[24]			An ankylosaur. Also found in the Lance and Scollard Formations.
Denversaurus[24]	Denversaurus schlessmani [24]	Montana[24] South Dakota[25]			A nodosaurid ankylosaur.

Pachycephalosaurs

An undescribed Pachycephalosaur is present in North Dakota.^[26]

Pachycephalosaurs reported from the Hell Creek Formation
Genus	Species	State	Stratigraphic position	Material	Notes	Images
Dracorex[27]	D. hogwartsia[27]	South Dakota[27]	Middle[27]		A pachycephalosaur, possibly synonymous with Pachycephalosaurus.
Pachycephalosaurus[24]	P. wyomingensis[24]	Montana[24] South Dakota[25]			A pachycephalosaur. Also found in the Lance Formation.
Sphaerotholus[24]	S. buchholtzae[24]	Montana[24]		"Skull material."[28]	A pachycephalosaur, possibly synonymous with Prenocephale.
Stygimoloch[24]	S. spinifer[24]	Montana[24] South Dakota North Dakota			A pachycephalosaur, possibly 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.^[10]

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[24]	Leptoceratops c.f. gracilis[24]		Montana[24]			A small primitive-looking ceratopsian.
Tatankaceratops	T. sacrisonorum		South Dakota			A ceratopsian possibly synonymous with Triceratops[29]
Torosaurus[7][24]	T. latus[7][24]		Montana[24] North Dakota[8][26] South Dakota[8][25]	Upper Hell Creek Formation[9]		A ceratopsian possibly synonymous with Triceratops.[30] A rare ceratopsid.[9]
Triceratops[7][24]	T. horridus[7][24]	T. serratus[24]	Montana[24] North Dakota[8][26] South Dakota[8][25]	Lowermost to upper Hell Creek Formation[9]	4 specimens are assigned to Triceratops horridus from the Hell Creek Formation[10]	A ceratopsian.[7] Also found in the Evanston, Frenchman, Lance, Laramie, and Scollard Formations.
	T. prorsus[24]		Montana[24]		Very common.	Also found in the Frenchman and Lance Formations.

Ornithopods

Indeterminate hadrosaurid remains are very common in the Hell Creek Formation.^[7] 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.^[24]

Ornithopods reported from the Hell Creek Formation
Genus	Species	Synonyms	State	Stratigraphic position	Material	Notes	Images
Edmontosaurus	E. annectens	Anatosaurus annectens[31] Anatotitan copei[31]	Montana[24] South Dakota[25] North Dakota(Mummy Fossil)		Very common.	A hadrosaur. Also found in the Denver, Frenchman, Lance, Laramie, and Scollard Formations.
Thescelosaurus[25]	T. garbanii[32]	Bugenasaura garbanii	Montana[32] South Dakota[33]
	T. infernalis	Bugenasaura infernalis				Nomen dubium
	T. neglectus[7][25]		North Dakota[8] South Dakota[8][25]	Lower to upper Hell Creek Formation[9]	50 specimens[10]	A small ornithopod. Also found in the Frenchman, Lance, Laramie, and Scollard Formations.[34]

Theropods

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

Theropod tracks have been found in South Dakota.^[25] An unnamed alvarezsaurid, closely related to the Asian genus Mononykus, is known from Montana.^[35] 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 centimetres (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. Palaeontologists known for years that there are oviraptorosaurs found in the Hell Creek Formation, but the fossil remains of the group remain relatively scarce. The velociraptorine Acheroraptor is also present in the latest Maastrichtian layers of the formation.

Tyrannosaurids

Tyrannosaurids reported from the Hell Creek Formation
Genus	Species	Synonyms	State	Stratigraphic position	Material	Notes	Images
Tyrannosaurus[7][24]	T. rex[7][24]	Albertosaurus megagracilis[24] Aublysodon molnari[24] Dinotyrannus megagracilis[24] Nanotyrannus lancensis?	Montana[24] North Dakota[8][26] South Dakota[8][25]	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.^[7] 15 specimens from the Hell Creek Formation are undetermined ornithomimids^[10]

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	South Dakota[36]			An ornithomimid. Numem nudum
Struthiomimus[25]	S. sedens[37]	Montana South Dakota North Dakota			A large ornithomimid similar to Gallimimus in size.[37]
Ornithomimus[25]	O. velox[37]	Montana			A ornithomimid.

Oviraptorosaurs

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[24][38]	A. wyliei[38]	North Dakota[8][38] South Dakota[8][38]	12 well-preserved specimens[9]	Lower to upper Hell Creek Formation[10]	It was thus 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.[38]
"Leptorhynchos"	"L." elegans	Montana			Leptorhynchos is an extinct genus of caenagnathid.

Eumaniraptorans

Historically, numerous teeth have been attributed to various dromaeosaurid and troodontid taxa with known body fossils from only older formations, including Dromaeosaurus, Saurornitholestes, Richardoestesia, Troodon, and Paronychodon. 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.^[39]

Eumaniraptorans reported from the Hell Creek Formation
Genus	Species	State	Stratigraphic position	Material	Notes	Images
Acheroraptor[39]	A. temertyorum [39]	Montana[39] North Dakota?[7] South Dakota?[7]	Lower? to upper Hell Creek Formation[7]	Partial skull (one isolated maxilla, one dentary), teeth.[39]	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.[39]
Avisaurus[7][24]	A. archibaldi[7][24]	Montana[24] North Dakota[8] South Dakota[8]	Middle Hell Creek Formation[9]	One specimen from the Hell Creek Formation can be assigned to Avisaurus[10]	An avisaurid.[7]
Cimolopteryx[24]	C. maxima[24]	Montana[24]		It is known almost exclusively from a number of coracoids (a bone in the shoulder girdle).	A charadriiforme bird.
Dakotaraptor[40]	D. steini [40]	South Dakota[40]		Partial skeleton.[40]	A dromaeosaurid. Second largest dromaeosaurid known.[39]
Brodavis[41]	B. baileyi[41]	South Dakota[41]		Left tarsometatarsus missing proximal end, trochleae II and III.[41]	A hesperornithiform.[41]
Potamornis[41]	P.skutchi [42]	Montana[42]		the quadrate bone is unique in some respects but apparently shares more apomorphies with the family Hesperornithidae - the "typical" Hesperornithes - in cladistic analysis	A hesperornithiform.[41]
"Unnamed hesperornithiform A"[43]	Indeterminate	Montana[43]		Tarsometatarsus	A primitive hesperornithiform.[43] In addition to fossils from the Hell Creek Formation, Longrich, Tokaryk and Field (2011) assigned specimen RSM P 2315.1 from the Canadian Frenchman Formation to this taxon as well;[43] subsequently Martin, Kurochkin and Tokaryk (2012) made this particular specimen the holotype of the species Brodavis americanus.[41]
"Unnamed ornithurine B"[43]	Indeterminate[44]	Montana[45]		Partial coracoid	An ornithurine possibly similar to Cimolopteryx[43][44]
"Unnamed ornithurine C"[43]	Indeterminate			Partial coracoid	An ornithurine, also present in the Fort Union Formation, the only individual bird species known to have survived the Cretaceous–Paleogene extinction[43]
"Unnamed ornithurine D"[43]	Indeterminate			Partial coracoid	An ornithurine[43]

Pterosaurs

Pterosaurs of the Hell Creek Formation
Taxa	Species	State	Stratigraphic location	Material	Notes	Images
Azhdarchidae spp.	Indeterminate	Montana[46] 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, thought are not diagnostic to the generic level.[46]

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[47]	B. sternbergii[47]	Montana North Dakota South Dakota			Extinct genus of crocodylians that lived from the Late Cretaceous to the Eocene in North America.
Brachychampsa[47]	B. montana[47]	Montana South Dakota North Dakota			Extinct genus of alligatoroid.
Thoracosaurus[47]	T. neocesariensis[47]	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[48]	Indeterminate[48]	Montana[49]			Extinct genus of aquatic turtles belonging to the family Adocidae.
Compsemys[48]	C. victa[48]	Montana[49]			A relative of Dermatemydidae.
Peckemys	P. brinkman	Montana North Dakota			A relative of Baenidae.
Emarginachelys	E. cretacea	Montana			A relative of chelydrids.[50]
Eubaena[48]	E. cephalica[48]	Montana[49]			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[50]	H. clark[50]	North Dakota[50]			A kinosternoid related to the Central American river turtle.[50]
Plastomenus	P. sp				Trionychidae turtle.
Basilemys	B. sinuosa				Largest dermatemydid land tortoise.
Trionyx[48]	Indeterminate[48]	Montana[49]			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.

Squamates

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[51][52]	C. monstrosus[51][52]	Montana[51]			A platynotan lizard of uncertain phylogenetic placement, also known from the Lance Formation.[51]
Cerberophis[51][52]	C. robustus[51][52]	Montana[51]			An alethinophidian snake of uncertain phylogenetic placement.[51]
Obamadon[51][52]	O. gracilis[51][52]	Montana[51]			A polyglyphanodontian lizard of uncertain phylogenetic placement. Also known from the Lance Formation.[51]
Peneteius[51]	P. aquilonius[51]	Montana[51]			A chamopsiid polyglyphanodontian lizard.[51]
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[47]	C. sp.[47]	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[53]	C. minor[53]	Montana[53]			A multituberculate of uncertain phylogenetic placement.
Cimolodon[53]	C. nitidus	Montana North Dakota[53]			A cimolodontid multituberculate.
	C. cf. nitidus[53]	South Dakota[53]			A cimolodontid multituberculate.
	C. sp.[53]	North Dakota[53]			A cimolodontid multituberculate.
Cimolomys[53]	C. gracilis	Montana[53]			A cimolodontid multituberculate.
	C. cf. gracilis[53]	South Dakota[53]			A cimolomyid multituberculate.
Essonodon[53]	E. browni[53]	Montana[53]			A cimolomyid multituberculate.
Meniscoessus[53]	M. conquistus	South Dakota[53]			A cimolomyid multituberculate.
	M. robustus	Montana North Dakota South Dakota[53]			A cimolomyid multituberculate.
	M. cf. robustus	South Dakota[53]			A cimolomyid multituberculate.
	M. sp.	North Dakota[53]			A cimolomyid multituberculate.
	?M. sp.[53]	North Dakota[53]			A cimolomyid multituberculate.
Mesodma[53]	M. formosa	Montana South Dakota[53]			A neoplagiaulacid multituberculate.
	M. cf. formosa	Montana[53]			A neoplagiaulacid multituberculate.
	M. hensleighi	Montana South Dakota[53]			A neoplagiaulacid multituberculate.
	M. cf. hensleighi	South Dakota[53]			A neoplagiaulacid multituberculate.
	M. thompsoni	Montana North Dakota South Dakota[53]			A neoplagiaulacid multituberculate.
	M. cf. thompsoni	Montana[53]			A neoplagiaulacid multituberculate.
	M sp.[53]	Montana[53]			A neoplagiaulacid multituberculate.
	?M sp.[53]	Montana[53]			A neoplagiaulacid multituberculate.
?Neoplagiaulax[53]	?N. burgessi[53]	Montana[53]			A neoplagiaulacid multituberculate.
Paracimexomys[53]	P. priscus[53]	Montana[53]			A multituberculate of uncertain phylogenetic placement.
Paressonodon[54]	P. nelsoni[54]				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
Alphadon[53]	A. marshi	Montana North Dakota[53]			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[53]			An alphadontid.
	A. wilsoni	Montana[53]			An alphadontid.
	A. cf. wilsoni	Montana[53]			An alphadontid.
	A. sp.[53]	North Dakota South Dakota[53]			An alphadontid.
Didelphodon[53]	D. padanicus	South Dakota[53]			A stagodontid.
	D. vorax	Montana North Dakota[53]			A stagodontid. genus of Stagodontidae marsupials from the Late Cretaceous of North America.
	D. cf. vorax	South Dakota[53]			A stagodontid.
	D. sp.	North Dakota[53]			A stagodontid.
	cf. D. sp.[53]	North Dakota South Dakota[53]			A stagodontid.
Glasbius[53]	G. twitchelli	Montana[53]			A glasbiid.
	G. cf. twitchelli[53]	Montana[53]			A glasbiid.
Leptalestes[55]	L. cooki	Montana[53]			A pediomyid.
	L. krejcii[55]	Montana South Dakota[53]			A pediomyid.
Nanocuris[54]	N. improvida[54]				A deltatheridiid.
Nortedelphys	N. jasoni (= N. intermedius)[54][56]	Montana South Dakota			A herpetotheriid.
Pediomys[53]	P. elegans[53]	Montana South Dakota[53]			A pediomyid.
Protalphadon[53]	P. foxi	Montana[53]			An alphadontid.
	P. lulli[53]	Montana[53]			An alphadontid.
Protolambda[55]	P. florencae	Montana North Dakota South Dakota[53]			A pediomyid.
	P. hatcheri[55]	Montana South Dakota[53]			A pediomyid.
Turgidodon[53]	T. rhaister[53]	Montana[53]			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
Purgatorius	P. ceratops	Montana			A genus of the four extinct species believed to be the earliest example of a primate or a proto-primate.
Alostera[53]	A. saskatchewanensis[53]	Montana[53]			A eutherian of uncertain phylogenetic placement.
Batodon[53]	B. tenuis[53]	Montana[53]			A cimolestid eutherian.
Cimolestes[53]	C. cf. cerberoides	Montana[53]			A cimolestid eutherian.
	C. incisus	Montana[53]			A cimolestid eutherian.
	C. magnus	Montana North Dakota[53]			A cimolestid eutherian.
	C. propalaeoryctes	Montana[53]			A cimolestid eutherian.
	C. stirtoni[53]	Montana[53]			A cimolestid eutherian.
Gypsonictops[53]	G. hypoconus	Montana South Dakota[53]			A gypsonictopsid eutherian.
	G. illuminatus	Montana North Dakota[53]			A gypsonictopsid eutherian.
	G. cf. illuminatus	Montana[53]			A gypsonictopsid eutherian.
	G. sp.[53]	Montana[53]			A gypsonictopsid eutherian.
cf. Paranyctoides[53]	cf. Paranyctoides sp.[53]	Montana[53]			A nyctitheriid eutherian.
Protungulatum[55]	P. coombsi[55]	Montana[55]			A eutherian of uncertain phylogenetic placement; a basal eutherian or an arctocyonid condylarth.

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 flood plain 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.^[57][58] 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 fruit Spinifructus antiquus of unknown family and order, from the Hell Creek Formation in Montana

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)

• 

  ferns found in Hell Creek.

• 

  Cycads also found in Hell Creek.

• 

  Monkey-puzzle leaves are found in Hell Creek.

• 

  Ginkgo (uncommon) found in Hell Creek.

• 

  Various angiosperms found in Hell Creek.

• 

  Palm trees means the climate was warmer than now.

• 

  Redwood seed cones are known from Hell Creek.

• 

  Laurus are found in Hell Creek.

• 

  Cercidiphyllum are found in Hell Creek.

• 

  Magnolia is commonly found in Hell Creek.

Plant of the Hell Creek Formation:

• various ferns and cycads.
• Equisetum (Equisetaceae)

Gymnosperms

• Platyspiroxylon (Cupressaceae)
• Podocarpoxylon (Podocarpaceae)
• Elatocladus (Taxodiaceae)
• Sequoiaxylon (Taxodiaceae)
• Taxodioxylon (Taxodiaceae)
• Araucaria (Araucariaceae)
• very widespread Mesozoic conifer group. All members are extinct (Cheirolepidiaceae)

Ginkgos

• Baeria
• Ginkgo adiantoides

Angiosperms

• Artocarpus (Moraceae)
• Cercidiphyllum (Cercidiphyllaceae)
• Dombeyopsis (Sterculiaceae)
• Platanus (Platanaceae)
• Magnolia (Magnoliaceae)
• palms (Arecaceae)
• Barberryfamily (Berberidaceae)
• family includes today's American sycamore or plane tree (Platanaceae)
• Laurel family (Lauraceae)

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.

Plant 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 cycad. Uncommon. A distant living relative is our sago palm.
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				sea above.
Populus	P. nebrascensis
Cocculus	cf. C. flabella
Cissites	cf. C. acerifolia
Pistia	cf. P. corrugata				Floating aquatic herb.
Palaeoaster	P. inquirenda				Angiosperm. Produces large seed pods.

See also

• List of fossil sites (with link directory)
• List of dinosaur-bearing rock formations

Footnotes

1. 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. doi:10.1016/j.epsl.2011.03.008.
2. 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.
3. 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.
4. Lofgren, D.F. (1997). "Hell Creek Formation". In: Currie, P.J. & Padian, K., editors (1997). The Encyclopedia of Dinosaurs. San Diego: Academic Press. pp. 302–303. ISBN 978-0-122-26810-6.
5. Breithaupt, B.H. (1997). "Lance Formation". In: Currie, P.J. & Padian, K., editors (1997). The Encyclopedia of Dinosaurs. San Diego: Academic Press. pp. 394–395. ISBN 978-0-122-26810-6.
6. Eberth, D.A. (1997). "Edmonton Group". In: Currie, P.J. & Padian, K., editors (1997). The Encyclopedia of Dinosaurs. San Diego: Academic Press. pp. 199–204. ISBN 978-0-122-26810-6.
7. Pearson et al. (2002) p. 154
8. Pearson et al. (2002) pp. 145–167
9. Pearson et al. (2002) p. 155
10. Pearson et al. (2002) pp. 156
11. Listed as "cf. Barbourula sp." in "Class Amphibia," Estes and Berberian, (1970). Page 4.
12. "Class Amphibia," in Estes and Berberian, (1970). Page 4.
13. "Class Amphibia," in Estes and Berberian, (1970). Page 4. All taxa listed occur in Montana, see page 1.
14. Listed as "Eopelobates? sp." in "Class Amphibia," Estes and Berberian, (1970). Page 4.
15. 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.
16. "Class Osteichthyes," in Estes and Berberian, (1970). Page 3.
17. "Class Osteichthyes," in Estes and Berberian, (1970). Page 3. All taxa listed occur in Montana, see page 1.
18. "Class Osteichthyes," in Estes and Berberian, (1970). Page 4.
19. "Class Osteichthyes," in Estes and Berberian, (1970). Page 4. All taxa listed occur in Montana, see page 1.
20. Listed as "cf. Paralbula casei" in "Class Osteichthyes," Estes and Berberian, (1970). Page 4.
21. Todd D. Cook, Michael G. Newbrey, Donald B. Brinkman and 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).
22. "Class Chondrichthyes," in Estes and Berberian, (1970). Page 3.
23. "Class Chondrichthyes," in Estes and Berberian, (1970). Page 3. All taxa listed occur in Montana, see page 1.
24. "Dinosaur distribution (Late Cretaceous; North America; Montana)." Weishampel, et al. (2004). Page 584.
25. "Dinosaur distribution (Late Cretaceous; North America; South Dakota)." Weishampel, et al. (2004). Page 586.
26. "Dinosaur distribution (Late Cretaceous; North America; North Dakota)." Weishampel, et al. (2004). Page 585.
27. Bakker et al. (2006)
28. "Table 21.1," in Weishampel, et al. (2004). Page 465.
29. Nicholas R. Longrich (2011). "Titanoceratops ouranous, a giant horned dinosaur from the Late Campanian of New Mexico". Cretaceous Research 32. doi:10.1016/j.cretres.2010.12.007.
30. Scannella, J. and Horner, J.R. (2010). "Torosaurus Marsh, 1891, is Triceratops Marsh, 1889 (Ceratopsidae: Chasmosaurinae): synonymy through ontogeny." Journal of Vertebrate Paleontology, 30(4): 1157 - 1168. doi:10.1080/02724634.2010.483632
31. Campione, N.E. and 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. doi:10.1371/journal.pone.0025186
32. Listed as "?Thescelosaurus garbanii" in "Dinosaur distribution (Late Cretaceous; North America; Montana)." Weishampel, et al. (2004). Page 584.
33. Noted as being present, although misspelled as "Thescelosaurus garbani, in " "Dinosaur distribution (Late Cretaceous; North America; South Dakota)." Weishampel, et al. (2004). Page 586.
34. Boyd, Brown, et al. (2009)
35. Hutchinson and Chiappe, 1998. The first known alvarezsaurid (Theropoda: Aves) from North America. Journal of Vertebrate Paleontology. 18(3), 447–450.
36. 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
37. Longrich (2008), pages 983-996.
38. 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. doi:10.1371/journal.pone.0092022.
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References

• 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 (Boulder, Colorado). The Hell Creek Formation and the Cretaceous-Tertiary boundary in the northern Great Plains: An integrated continental record of the end of the Cretaceous: 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.
• 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. and Peterson, J.E. "An azhdarchid pterosaur cervical vertebra from the Hell Creek Formation (Maastrichtian) of southeastern Montana." Journal of Vertebrate Paleontology, 26(1): 192–195.
• 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.

External links

• Cretaceous Hell Creek Faunal Facies provides a faunal list.
• Phillip Bigelow, "Hell Creek life: Fossil Flora & Fauna, a Paleoecosystem"
• Paleobiology Database: MPM locality 3850 (Hell Creek Formation): Maastrichtian, Montana

Cretaceous Period
Lower/Early Cretaceous	Upper/Late Cretaceous
Berriasian | Valanginian | Hauterivian Barremian| Aptian | Albian	Cenomanian | Turonian | Coniacian Santonian |Campanian | Maastrichtian