Paleobiota of the Hell Creek Formation

This is an overview of the fossil flora and fauna of the Maastrichtian-Danian Hell Creek Formation.

Invertebrates

Insects

Insects from the groups Diptera, Zygoptera, and possibly Hemiphlebiidae have been unearthed in Hell Creek in amber.^[1][2] Fossils found in the Hell Creek Formation and the Fort Union Formation of these insects went extinct during the K-T Event.^[3][4][5]

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.

Genus	Species	Location	Stratigraphic position	Material	Notes	Images
Cephaloleichnites	Cephaloleichnites strongi				Possible hispine beetle herbivory on Zingiberopsis attenuta
?Hemiphlebiidae[2]	Indeterminate				Possible Hemiphlebiid damselflies
Brachycera[1]	Indeterminate				Undescribed brachyceran flies
Nematocera[1]	Indeterminate				Undescribed nematoceran flies
Aeschnidiidae[6]	Indeterminate				Indeterminate aeschnidiid dragonflies

Molluscs

Genus	Species	Location	Stratigraphic position	Material	Notes	Images
Plesielliptio	P. postbiplicatus				Freshwater Unionid river mussels
	P. gibbosoides				Freshwater Unionid river mussels
	P. whitfieldi				Freshwater Unionid river mussels
Rhabdotophorus	R. aldrichi				Freshwater mussel of family Unionidae.[7]
Pleurobema	P. cryptorhynchus				Freshwater mussel of family Unionidae.[7]
Plethobasus	P. aesopiformis				Freshwater mussel of family Unionidae.[7]
	P. biesopoides
Quadrula	Q. cylindricoides				Freshwater mussel of family Unionidae.[7]
Proparreysia	P. verrucosiformis				Freshwater mussel of family Unionidae.[7]
	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	South Dakota			From a marine facies ("tongue"). Modern members of the 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.

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.

Genus	Species	Location	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]	Montana[14]
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]	Montana[14]
Habrosaurus[8][13]	H. dilatus[8][13]	Montana[14] North Dakota[9] South Dakota[9]	Middle to upper Hell Creek Formation[10]	6 specimens[11]	Habrosaurus is a sirenid amphibian.[8]
Lisserpeton[13]	L. bairdi[13]	Montana[14]
Opisthotriton[8][13]	O. kayi[8][13]	Montana[14] North Dakota[9] South Dakota[9]	Lower to upper Hell Creek Formation[10]	22 specimens[11]	Opisthotriton is classified as a Batrachosauroididae.[8]
Paranecturus[16]	P. garbanii[16]	Montana[16]			A member of Proteidae.[16]
Proamphiuma[13]	P. cretacica[13]	Montana[14]
Prodesmodon[13]	P. copei[13]	Montana[14]
Scapherpeton[8][13]	S. tectum[8][13]	Montana[14] North Dakota[9] South Dakota[9]	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]	Montana[14]			A small frog

Fish

Bony fish

Bony fishes
Genus	Species	Location	Stratigraphic position	Material	Notes	Images
Acipenser[8][17][18]	A. amnisinferos[18]	North Dakota (Tanis)[18]			A sturgeon
	A. eruciferus[17]	Montana[19]
	A. praeparatorum[18]	North Dakota (Tanis)[18]
	A. cf. A. amnisinferos[18]	North Dakota (Tanis)[18]
	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]
Anchiacipencer[20]	A. acanthaspis[20]	Montana[20]			A sturgeon, originally considered as indeterminate material[20]
Belonostomus[8][17]	B. longirostris[8][17]	Montana[19] North Dakota[9] South Dakota[9]	Lower to upper Hell Creek Formation[10]	28 specimens[11]	A long-snouted slender fish classified as an aspidorhynchid.[8]
Coriops[21]	C. amnicolus[21]	Montana[22]
Cyclurus[17]	C. fragosus[17]	Montana[19] North Dakota[9] South Dakota[9]			A small amiid fish (ubiquitous). Previously known as Amia fragosa or Kindleia fragosa.[23] 2610 specimens have been assigned to Kindleia, making it an extremely common genus.[11]	Cyclurus kehreri from Messel Pit, species within same genus as C. fragosus
"Lepisosteus"[8][17]	"L. occidentalis"[8][17]	Montana[19] North Dakota[9] South Dakota[9]	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] Nomen dubium.[24]
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]	Montana[19]
Paleopsephurus[17]	P. wilsoni[17]	Montana[19]			A paddlefish
Paralbula[25]	P. casei[25]	Montana[22]
Parapsephurus[26]	P. willybemisi[26]	North Dakota (Tanis)[26]			A paddlefish
Platacodon[21]	P. nanus[21]	Montana[22]			Small teleost fish
Protamia[17]	Indeterminate[17]	Montana[19]
Pachyrhizodontoidei	Indeterminate				Fish
Polyodontidae[27]	Indeterminate[27]	Montana[27]			Paddlefish
Protoscaphirhynchus[17]	P. squamosus[17]	Montana[19]			A sturgeon
Pugiopsephurus[26]	P. inundatus[26]	North Dakota (Tanis)[26]			A paddlefish

Cartilaginous fish

Chondrichthyes reported from the Hell Creek Formation
Genus	Species	Location	Stratigraphic position	Material	Notes	Images
Chiloscyllium[28]	C. sp.[28]	Montana[28]			A member of Hemiscylliidae.[28]
Galagadon[29]	G. nordquistae	South Dakota		Isolated teeth	A carpet shark
Lonchidion[30]	L. selachos[30]	Montana[31] North Dakota[9] South Dakota[9]	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[28]	M. pustulosus[28]	Montana[28] North Dakota[9] South Dakota[9]	Lower to upper Hell Creek Formation.[10]	1677 specimens[11] previously assigned to M. bipartitus.[28]	Is an anacoracid batoid[8] rajiform related to guitarfishes.[28] Described on the basis of teeth formerly assigned to the species M. bipartitus.[28] The material assigned to Myledaphus bipartitus and makes up 16.5% of the vertebrate remains.[8]
Protoginglymostoma[28]	P. estesi[28]	Montana[28]			A member of Ginglymostomatidae.[28] Formerly assigned to the genus Brachaelurus.
Restesia[28]	R. americana[28]	Montana[28] North Dakota[9] South Dakota[9]	Middle Hell Creek Formation[10]	5 specimens previously assigned to Squatirhina[11]	A wobbegong-like shark.[28] Formerly assigned to Squatirhina. The remains consist of 0.05% of the vertebrates.[11] Also known from the Lance Formation.[28]
Carcharhinidae indet.[29]	Indeterminate	South Dakota		An isolated tooth.
Scapanorhynchus[32]	.sp.	North Dakota

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.^[33]

• Ceratopsidae 61%
• Hadrosauridae 23%
• Ornithomimidae 5%
• Tyrannosauridae 4%
• Hypsilophodontidae 3%
• Dromaeosauridae 2%
• Pachycephalosauridae 1%
• Ankylosauridae 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 (more likely Pectinodon), 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.^[34] A trackway made by mid-sized theropod, possibly a small tyrannosaurid individual, was discovered in South Dakota in 1997, and in 2014 these footprints were named Wakinyantanka styxi.^[35]

Ornithischians

Ankylosaurs

Indeterminate nodosaur remains have been unearthed in the Hell Creek Formation and other nearby areas.^[36][37]

Ankylosauria reported from the Hell Creek Formation
Genus	Species	State	Stratigraphic position	Material	Notes	Images
Ankylosaurus[38]	A. magniventris[38]	Montana[38]	Upper	A partial skull, teeth, cervical vertebrae, dorsal vertebrae, caudal vertebrae, right scapulocoracoid, otic capsule, maxilla fragment, right jugal, left jugal and quadratojugal, sacral centra, additional fragments of the cervical half rings and a partial tail club handle.	An ankylosaur. Also found in the Lance, Frenchman, Ferris and Scollard Formations.
Denversaurus[39]	D. schlessmani[39]	South Dakota[36]	Lower[36]	A complete skull without the lower jaw and associated plates (DMNH 468)[36]	A nodosaurid ankylosaur whose remains have been also found in the Lance Formation[40]

Pachycephalosaurs

An undescribed and unnamed pachycephalosaur is present in North Dakota.^[41] Pachycephalosaur remains have been unearthed in Montana as in the case of Platytholus and the now invalid genus Stenotholus kohleri, which is now a junior synonym of Pachycephalosaurus.^[42] Dracorex hogwartsia is agreed by paleontologists to be an ontogimorph of either Pachycephalosaurus or Stygimoloch, while the synonymy of Stygimoloch spinifer with Pachycephlosaurus remains uncertain due to difference in stratigraphic level.^[43][44][45]

Pachycephalosaurs reported from the Hell Creek Formation
Genus	Species	State	Stratigraphic position	Material	Notes	Images
Pachycephalosaurus[38]	P. wyomingensis[38]	Montana[38] South Dakota[46]			A pachycephalosaur. Also found in the Lance Formation.
Platytholus[47]	P. clemensi[47]	Montana[47]	Lower[47]	A partial skull[47]	A medium-sized pachycephalosaurine closely related to Acrotholus and Prenocephale
Sphaerotholus[38]	S. buchholtzae[38]	Montana[38]	Lower to upper[48][49]	"Skull material."[50]	A pachycephalosaur whose remains have also been found in the Frenchman Formation. Genus also known from the Kirtland Formation, Dinosaur Park Formation and the Horseshoe Canyon Formation.
	S. triregnum[49]	Montana[49]	Middle[49]	A left squamosal.[49]	A pachycephalosaur distinguished from S. buchholtzae by its more ornamented squamosal.[49]
Stygimoloch[38]	S. spinifer[38]	Montana[38] South Dakota North Dakota			A pachycephalosaur, possibly synonymous with Pachycephalosaurus. Also found in the Ferris Formation and the Lance Formation.

Ceratopsians

Indeterminate ceratopsid teeth and some identifiable bones from Triceratops can be extremely common.^{[51][52][53][54][55]} 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.^[56][57][58]

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[38]	L. gracilis[38]		Montana[38]			A small primitive-looking ceratopsian. Fossils have also been found in the Lance Formation in Wyoming.[59]
Tatankaceratops[60]	T. sacrisonorum[60]		South Dakota[60]			A controversial ceratopsian possibly synonymous with Triceratops[61]
Torosaurus[8][38]	T. latus[8][38]		Montana[38] North Dakota[9][41] South Dakota[9][46]	Upper Hell Creek Formation[10]		A ceratopsian that was once proposed to be synonymous with Triceratops,[62] but is now regarded as a valid and distinct ceratopsian.[63] A rare ceratopsid.[10] Fossils have been in the Lance Formation, Javelina Formation, North Horn Formation, Laramie Formation, El Picacho Formation, Frenchman Formation and Scollard Formation.
Triceratops[8][38]	T. horridus[8][38]	T. serratus[38] Ugrosaurus olsoni[64]	Montana[38] North Dakota[9][41] Wyoming South Dakota[9][46]	Lowermost to the middle Hell Creek Formation[65]	Four specimens are assigned to Triceratops horridus from the Hell Creek Formation.[11] Isolated, shed ceratopsid teeth are incredibly common in the Hell Creek and Lance Formations, being by most collectors, with some being nothing more than worn down fragments up to superb teeth containing complete, preserved roots. Because the teeth of different ceratopsians are so similar to one another, its hard to differentiate between genera/species, but based on the abundance of identifiable bones belonging to Triceratops in Lancian-aged North American formations, especially the Hell Creek, isolated ceratopsid teeth from the lower and middle Hell Creek Formation have a high likelihood of originating from T. horridus.	A ceratopsian.[8] Also found in the Evanston, Frenchman, Lance, Laramie, and Scollard Formations.
	T. prorsus[38]		Montana[38] South Dakota	Upper 1/3 of the Hell Creek Formation[65]	Very common.[citation needed] Because the teeth of different ceratopsians are so similar to one another, its hard to differentiate between genera/species, but based on the abundance of identifiable bones belonging to Triceratops in Lancian-aged North American formations, especially the Hell Creek, isolated ceratopsid teeth from the upper 1/3 of the Hell Creek Formation have a high likelihood of originating from T. prorsus.	Also found in the Frenchman and Lance Formations.

Ornithopods and relatives

Indeterminate hadrosaurid remains are very common in the Hell Creek Formation.^[8] Fossils of indeterminate lambeosaurs have been unearthed in Hell Creek, specifically in South Dakota and Montana.^{[66][67][68][69][70][71]}

Ornithopods and Thescelosaurs reported from the Hell Creek Formation
Genus	Species	Synonyms	State	Stratigraphic position	Material	Notes	Images
Edmontosaurus	E. annectens	Anatosaurus annectens[72] Anatotitan copei[72]	Montana[38] South Dakota[46] North Dakota(Mummy Fossil)[73][74]		Very common.	A hadrosaur. Also found in the Denver, Frenchman, Lance, Laramie, and Scollard Formations.[75][76] Hatchlings have also been unearthed.[76]
Thescelosaurus[46]	T. garbanii[77][78]	Bugenasaura garbanii[78]	Montana[77] South Dakota[79]
	T. neglectus[8][46]		North Dakota[9] South Dakota[9][46]	Lower to upper Hell Creek Formation[10]	50 specimens[11]	A small thescelosaurine. Also found in the Frenchman, Lance, Laramie, and Scollard Formations.[80] Two species are known from Hell Creek; T. neglectus and T. garbanii.[81]

Theropods

Theropod tracks have been found in South Dakota.^[46] A trackway from South Dakota, named Wakinyantanka, was made by a mid-sized theropod with three slender toes, possibly a small tyrannosaurid.^[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.^[82] 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, though in past albertosaurine remains have described here but its most likely that they are the remains of Tyrannosaurus rex.^[83][84] Theropod remains are very common in Hell Creek, some of which belong to indeterminate species on maniraptorans.^[85]

Alvarezsaurs

Alvarezsaurs reported from the Hell Creek Formation
Genus	Species	Synonyms	State	Stratigraphic position	Material	Notes	Images
"Ornithomimus"	"O." minutus
Trierarchuncus[86]	T. prairiensis[86]		Montana[38]	upper Hell Creek Formation.		An alvarezsaur known from a partial post-cranial skeleton.[87]

Tyrannosaurids

Tyrannosaurids reported from the Hell Creek Formation
Genus	Species	Synonyms	State	Stratigraphic position	Material	Notes	Images
Tyrannosaurus[8][38]	T. rex[8][38]	Albertosaurus megagracilis[38] Aublysodon molnari[38] Dinotyrannus megagracilis[38] Nanotyrannus lancensis?	Montana[38] North Dakota[9][41] South Dakota[9][46]	Lower to upper Hell Creek Formation.		A tyrannosaur, known from several specimens including a juvenile nicknamed "Jane".[88] 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. Isolated teeth in the Hell Creek are common enough to be dug commercially by collectors, but rare enough that they are often sold for very high prices with fragmentary teeth usually beginning at least in the hundreds of USD, and complete teeth in the thousands of USD. Perhaps the best known iconic dinosaur.
Nanotyrannus?[8][38]	N.lancensis[8][38]	Stygivenator? Deinodon lancensis Albertosaurus lancensis[38] Tyrannosaurus lancensis?	Montana Wyoming	Lower to upper Hell Creek Formation.	A few specimens are known	Invalid genus, now recognised as juvenile T. rex.

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	South Dakota[89]		One partial skeleton.	An ornithomimid; nomen nudum.
Struthiomimus[46]	S. sedens[90]	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.[90]
Ornithomimus	O. velox[90]	Montana South Dakota North Dakota		Fragmentary specimens	An ornithomimid which was also found in the Denver Formation.

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 the past, oviraptorosaur fossils found were thought to have belonged to Leptorhynchos, Caenagnathus, Chirostenotes, and Elmisaurus.^{[38][91][92][93][94][95]} In 2016, an undescribed large-bodied caenagnathid was unearthed in Montana.^[96]

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[38][91]	A. wyliei[91]	North Dakota[9][91] South Dakota[9][91]	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.[91]
Caenagnathidae	Indeterminate	Montana			Similar to Citipes and Elmisaurus.
Eoneophron	E. infernalis	South Dakota[97]		A partial right hindlimb[97]	Closely related to Citipes and Elmisaurus.[97]

Eumaniraptorans

Historically, numerous teeth have been attributed to various dromaeosaurid and troodontid taxa with known body fossils from only older formations, including Saurornithoides, Zapsalis, 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 seemingly disproven in 2015, when DePalma et al., described the new genus Dakotaraptor, a large species of dromaeosaur.^[98] However, Dakotaraptor’s validity has been called into question since, as the holotype may be a chimeric assemblage of various non-dromaeosaurid coelurosaurians.^[99] Fossilized teeth of various troodontids and coelurosaurs are common throughout the Hell Creek Formation; the best known examples include Paronychodon, Pectinodon and Richardoestesia, respectively. Teeth belonging to possible intermediate species of Dromaeosaurus^[100] and Saurornitholestes^[101] have been unearthed at the Hell Creek Formation and the nearby Lance Formation.

Eumaniraptorans reported from the Hell Creek Formation
Genus	Species	State	Stratigraphic position	Material	Notes	Images
Acheroraptor[98]	A. temertyorum [98]	Montana[98] North Dakota?[8] South Dakota?[8]	Lower? to upper Hell Creek Formation[8]	ROM 63777, a maxilla and tooth[98] ROM 63778, a partial dentary[98] isolated teeth[98]	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.[98]
Avisaurus[8]	A. archibaldi[8][38]	Montana[8]	Middle Hell Creek Formation[10]	UCMP 117600, holotype, a tarsometatarsus PU 17324, a tarsometatarsus	An avisaurid.[8]
	cf. A. archibaldi[102]	Montana[102]	Uppermost Hell Creek Formation[102]	YPM 57235, a coracoid	An avisaurid tentatively referred to A. archibaldi based on its size.[102]
	A. darwini[103]	Montana		DDM 1577.730, a right tarsometatarsus
	A. sp.[104]	Montana[104]		distal tarsals, metatarsus (juvenile)[104] MOR3070, a partial right tarsometatarsus
Brodavis[105]	B. baileyi[105]	South Dakota[105]		UNSM 50665, a left tarsometatarsus missing proximal end, trochleae II and III.[105]	A primitive hesperornithiform.[105]
Dakotaraptor[106]	D. steini [106]	South Dakota[106]	Upper Hell Creek Formation[106]	PBMNH.P.10.113.T, a partial skeleton.[106] PBMNH.P.10.115.T, a tibia.[106] PBMNH.P.10.118.T, an astragalocalcaneum.[106] isolated teeth.[106]	A large dromaeosaurid. Possibly chimeric.[98][99]
Magnusavis[103]	M. ekalakaensis	Montana		CCM V2019.5.1, partial right tarsometatarsus and toe bone	A large enantiornithine closely related to avisaurids.
Paronychodon[107]	P. caperatus[107]	North Dakota, South Dakota, and Montana.		YPM 10624, a fossilized tooth. Teeth of this genus have been found too.	A troodontid theropod who is known from fossil teeth. Fossils have also been found in the Lance Formation in Wyoming.
Pectinodon[108][107]	P. bakkeri[108][107]	Montana		UCM 38445, a fossilized tooth. Teeth of this genus have been found too.	A troodontid theropod who is known from fossil teeth. Fossils have also been found in the Lance Formation in Wyoming.
Potamornis[105]	P. skutchi [109]	Montana[109]		UCMP 117605, a tarsometatarsus	A hesperornithiform also found in the Lance Formation.[109]
Richardoestesia[110][111]	R. sp.[110][111]	Montana.		Teeth.	A coelurosaur that is known from teeth and from two species Richardoestesia gilmorei and Richardestesia isosceles, which have also been unearthed in the Lance Formation in Wyoming.
"Styginetta"[112]	"S. lofgreni."	Montana.			A Presbyornithid, it is notable for being one of the few birds known to have survived the Cretaceous–Paleogene extinction event.
"Unnamed enantiornithine B"[102]	Unnamed	Montana[102]		YPM 57823, a partial coracoid[102]	An unnamed enantiornithean.[102]
"Unnamed hesperornithiform A"[102]	Unnamed	Montana		UCMP 13355, a tarsometatarsus	A primitive hesperornithiform.[105] The Hell Creek specimen was referred to the same unnamed taxon as RSM P 2315.1 from the Canadian Frenchman Formation.[102] RSM P 2315.1 was later made the holotype of Brodavis americanus.[105] May be a synonym of Potamornis.[102]
"Unnamed ornithurine B"[102]	Unnamed[113]	Montana[114]		UCMP 129143, a partial coracoid[102]	An ornithurine possibly similar to Cimolopteryx[102][113]
"Unnamed ornithurine C"[102]	Unnamed	Montana[102] South Dakota[102]		SDSM 64281A, a partial coracoid[102] SDSM 64281B, a partial coracoid[102] UCMP 175251, a partial coracoid[102] MOR 2918, a partial coracoid[102]	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[102]
"Unnamed ornithurine D"[102]	Unnamed	Montana[102]		UCMP 187207, a partial coracoid[102]	An ichthyornithean also present in the Frenchman Formation[102]

Pterosaurs

Undescribed pterosaur remains were reported from North Dakota.^[115] Undescribed pteranodontian specimen has also been mentioned in the supplementary material of Longrich et al. (2018).^[116]

Pterosaurs of the Hell Creek Formation
Taxa	Species	State	Stratigraphic location	Material	Notes	Images
Infernodrakon[117]	I. hastacollis	Montana[115]			A single azhdarchid neck bone originally considered to belong to the genus Quetzalcoatlus.[115]

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[118]	B. sternbergii[118]	Montana North Dakota South Dakota			Extinct genus of crocodylians that lived from the Late Cretaceous to the Eocene in North America.
Brachychampsa[118]	B. montana[118]	Montana South Dakota North Dakota			Extinct genus of alligatoroid.
Thoracosaurus[118]	T. neocesariensis[118]	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[119]	Indeterminate[119]	Montana[120]			Extinct genus of aquatic turtles belonging to the family Adocidae.
Axestemys[121]	A. infernalis[121]	Montana North Dakota South Dakota Wyoming			A turtle belonging to the family Trionychidae. Its fossils from the Hell Creek Formation were formerly assigned to the late Campanian species Axestemys splendidus.[122][121]
Compsemys[119]	C. victa[119]	Montana[120]			A relative of Dermatemydidae.
Peckemys	P. brinkman	Montana North Dakota			A relative of Baenidae.
Emarginachelys	E. cretacea	Montana			A relative of chelydrids.[123]
Eubaena[119]	E. cephalica[119]	Montana[120]			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[123]	H. clark[123]	North Dakota[123]			A kinosternoid related to the Central American river turtle.[123]
Hutchemys[124]	H. walkerorum[124]	North Dakota[124]		A shell[124]	A Plastomeninae related to the softshell turtle.[124]
Plastomenus	P. sp				Trionychidae turtle.
Basilemys	B. sinuosa				Largest dermatemydid land tortoise.
Trionyx[119]	Indeterminate[119]	Montana[120]			A genus of softshell turtles belonging to the family Trionychidae.
Aspideretoides	A. foveatus				Trionychidae turtle.
Helopanoplia	H. distincta				Trionychidae turtle.
Judithemys	J. 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.
Saxochelys[125]	S. gilberti	North Dakota		A population of over 30 individual skeletons	A member of the family Baenidae.
Thescelus	T. insiliens				Baenid turtle.
Chelydridae	Indeterminate				Chelydrids-like turtle.

Squamata

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[126][127]	C. monstrosus[126][127]	Montana[126]			A platynotan lizard of uncertain phylogenetic placement, also known from the Lance Formation.[126]
Cerberophis[126][127]	C. robustus[126][127]	Montana[126]			An alethinophidian snake of uncertain phylogenetic placement.[126]
Obamadon[126][127]	O. gracilis[126][127]	Montana[126]			A polyglyphanodontian lizard of uncertain phylogenetic placement. Also known from the Lance Formation.[126]
Peneteius[126]	P. aquilonius[126]	Montana[126]			A chamopsiid polyglyphanodontian lizard.[126]
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.
Mosasaurinae	Indeterminate	North Dakota			Indeterminate mosasaurine remains have been unearthed in North Dakota; they may belong to a mosasaur measuring 11 m (36 ft) in length.[128][129]

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[118]	C. sp.[118]	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[130]	C. minor[130]	Montana[130]			A multituberculate of uncertain phylogenetic placement.
Cimolodon[130]	C. nitidus	Montana North Dakota[130]			A cimolodontid multituberculate.
	C. cf. nitidus[130]	South Dakota[130]			A cimolodontid multituberculate.
	C. sp.[130]	North Dakota[130]			A cimolodontid multituberculate.
Cimolomys[130]	C. gracilis	Montana[130]			A cimolomyid multituberculate.
	C. cf. gracilis[130]	South Dakota[130]			A cimolomyid multituberculate.
Essonodon[130]	E. browni[130]	Montana[130]			A cimolomyid multituberculate.
Meniscoessus[130]	M. conquistus	South Dakota[130]			A cimolomyid multituberculate.
	M. robustus	Montana North Dakota South Dakota[130]			A cimolomyid multituberculate.
	M. cf. robustus	South Dakota[130]			A cimolomyid multituberculate.
	M. sp.	North Dakota[130]			A cimolomyid multituberculate.
	?M. sp.[130]	North Dakota[130]			A cimolomyid multituberculate.
Mesodma[130]	M. formosa	Montana South Dakota[130]			A neoplagiaulacid multituberculate.
	M. cf. formosa	Montana[130]			A neoplagiaulacid multituberculate.
	M. hensleighi	Montana South Dakota[130]			A neoplagiaulacid multituberculate.
	M. cf. hensleighi	South Dakota[130]			A neoplagiaulacid multituberculate.
	M. thompsoni	Montana North Dakota South Dakota[130]			A neoplagiaulacid multituberculate.
	M. cf. thompsoni	Montana[130]			A neoplagiaulacid multituberculate.
	M sp.[130]	Montana[130]			A neoplagiaulacid multituberculate.
	?M sp.[130]	Montana[130]			A neoplagiaulacid multituberculate.
?Neoplagiaulax[130]	?N. burgessi[130]	Montana[130]			A neoplagiaulacid multituberculate.
Paracimexomys[130]	P. priscus[130]	Montana[130]			A multituberculate of uncertain phylogenetic placement.
Paressonodon[131]	P. nelsoni[131]				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[130]	A. marshi	Montana North Dakota[130]			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[130]			An alphadontid.
	A. wilsoni	Montana[130]			An alphadontid.
	A. cf. wilsoni	Montana[130]			An alphadontid.
	A. sp.[130]	North Dakota South Dakota[130]			An alphadontid.
Didelphodon[130]	D. padanicus	South Dakota[130]			A stagodontid.
	D. vorax	Montana North Dakota[130]			A stagodontid. genus of Stagodontidae marsupials from the Late Cretaceous of North America.
	D. cf. vorax	South Dakota[130]			A stagodontid.
	D. sp.	North Dakota[130]			A stagodontid.
	cf. D. sp.[130]	North Dakota South Dakota[130]			A stagodontid.
Glasbius[130]	G. twitchelli	Montana[130]			A glasbiid.
	G. cf. twitchelli[130]	Montana[130]			A glasbiid.
Leptalestes[132]	L. cooki	Montana[130]			A pediomyid.
	L. krejcii[132]	Montana South Dakota[130]			A pediomyid.
Nanocuris[131]	N. improvida[131]				A deltatheridiid.
Nortedelphys	N. jasoni (= N. intermedius)[131][133]	Montana South Dakota			A herpetotheriid.
Pediomys[130]	P. elegans[130]	Montana South Dakota[130]			A pediomyid.
Protalphadon[130]	P. foxi	Montana[130]			An alphadontid.
	P. lulli[130]	Montana[130]			An alphadontid.
Protolambda[132][134]	P. florencae[132][134]	Montana North Dakota South Dakota[130]			A pediomyid.
	P. hatcheri[132][134]	Montana South Dakota[130]			A pediomyid.
	P. mcgilli[135]	Montana[135]			A pediomyid.
Turgidodon[130]	T. rhaister[130]	Montana[130]			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 possible creodont, formerly a species of Cimolestes[136]
Alostera[130]	A. saskatchewanensis[130]	Montana[130]			A eutherian of uncertain phylogenetic placement.
Ambilestes	A. cerberoides	Montana			A eutherian of uncertain classification, formally a species of Cimolestes
Batodon[130]	B. tenuis[130]	Montana[130]			A cimolestid eutherian.
Cimolestes[130]	C. incisus	Montana[130]			A cimolestid eutherian.
	C. stirtoni[130]	Montana[130]			A cimolestid eutherian.
Gypsonictops[130]	G. hypoconus	Montana South Dakota[130]			A gypsonictopsid eutherian.
	G. illuminatus	Montana North Dakota[130]			A gypsonictopsid eutherian.
	G. cf. illuminatus	Montana[130]			A gypsonictopsid eutherian.
	G. sp.[130]	Montana[130]			A gypsonictopsid eutherian.
cf. Paranyctoides[130]	cf. Paranyctoides sp.[130]	Montana[130]			A nyctitheriid eutherian.
Protungulatum[132]	P. coombsi[132]	Montana[132]			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

Flora

The Hell Creek Formation was a low floodplain at the time before the sea retreated, and in the wet ground of the dense woodland, the diversity of angiosperms and conifers were present. An endless diversity of herbaceous flowering plants, ferns and moss grew in the forest understory. On the exposed point bars of large river systems, there were shrubs and vines. The evidence of the forested environment is overwhelmingly supported by petrified wood, rooted gley paleosols,^[137] and ubiquitous tree leaves. The presence of the simple and lobed leaves, combined with an extremely high dicot diversity, extinct cycadeoid Nilssoniocladus, Ginkgo, many types of monocots, and several types of conifers is different from any modern plant community. There are numerous types of leaves, seeds, flowers and other structures from Angiosperms, or flowering plants. The Hell Creek Formation of this layer contains over 300 tablets, of which angiosperms are by far the most diverse and dominant flora of the entire population, about 90 percent, followed by about 5% of conifers, 4% of ferns, and others. Compared to today Hell Creek's flora which is prairie, then Hell Creek's flora was hardwood forest mixed with deciduous and evergreen forest. In sharp contrast to the Great Plains today, the presence of many thermophilous taxa such as palm trees and gingers meant the climate was warmer and wetter then.

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

The plants of the Hell Creek Formation generally represent angiosperm-dominated riparian forests of variable diversity, depending on stratigraphic position and sedimentary environment. There appears to be floral transitions visible on a stratigraphic range from the lower to the upper Hell Creek Formation. For this reason, Kirk Johnson and Leo Hickey divided it into five zones and described them as HCIa, HCIb, HCIIa, HCIIb, and HCIII as a reflection of floral change through time.^[138] For example, the HCIa zone is dominated by "Dryophyllum" subfalcatum, Leepierceia preartocarpoides, "Vitis" stantonii, and "Celastrus" taurenensis, and is located 55 to 105 meters below the K-Pg boundary layer. Although the HCIb zone is a very thin layer, about 5 meters of rock, it bears unusually high diversity of herbaceous and shrubby plants, including Urticaceae, Ranunculaceae, Rosaceae, and Cannabaceae.^[139][140]

Bisonia niemii is one of the common fossil leaf species in the HCIII zone.

There is evidence of transitional floras in the middle of the Hell Creek Formation as shown by HCII and HCIII zones. The HCII flora represents a transitional period where taxa from the lower Hell Creek are replaced by the HCIII flora. The diversity of the HCIII zone is very high, and its composition is more uniform than that of HCII, many of which were rare or absent from the zones below, and some others that used to be common below became rarer in the HCIII zone. These forms include Elatides longifolia, "Dryophyllum" tennessensis, Liriodendrites bradacii, and many members of the Laurales including Bisonia niemii, "Ficus" planicostata, and Marmarthia trivialis, while "Celastrus" taurenensis, Leepierceia preartocarpoides, and many cupressaceous conifers became rarer. This phenomenon suggests that the global temperature was warming during the last 300,000-500,000 years of the Cretaceous period.^{[139][140][141][142]}

Johnson claims that there are no grasses, oaks, maples, beeches, figs, or willows in the Hell Creek Formation. There is no evidence of fern prairie either.^[143] However, there was an extremely high angiosperm diversity — common plane trees, "Dryophyllum" subfalcatum, Leepierceia preartocarpoides, and palm trees — along with extinct cycadeoid Nilssoniocladus, Ginkgo, araucariaceous, podocarpaceous, and cupressaceous conifers. This represents the mixed deciduous and evergreen broad-leaved forest as the Hell Creek landscape. The nature of these forests is uncertain because Johnson found that the majority of the angiosperm and conifer genera are now extinct. He also believes that, very roughly 80% of the terrestrial plant taxa died out in what is now Great Plains at the K-Pg boundary. On other hand, 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-Pg boundary layer). This increase in fern spore abundance is commonly referred 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).

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 Ficus 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. Among the localities, the Mud Buttes, located in Bowman County, North Dakota, is probably the richest megaflora assemblage known and the most diverse leaf quarry from the Hell Creek Formation.^[140] "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; "DMNH" is for the Denver Museum of Nature & Science; "USNM" is for Smithsonian National Museum of Natural History; and so on. The majority of Hell Creek megafloral specimens are collected at the Denver Museum of Nature & Science.

Overview (from Johnson, 2002)

302 plant morphotypes based on leaf only, including:

• 1 bryophyte (mosses and liverworts)
• 11 ferns
• 1 sphenopsid
• 10 conifers
• 1 ginkgo (uncommon)
• 278 angiosperms (roughly 92% of all taxa found)

Paleoflora

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.

Liverworts

Genus	Species	Location	Stratigraphic position	Abundance	Notes	Images
Marchantia	M. pealii				Only known liverwort in Hell Creek.

Ferns

Genus	Species	Location	Stratigraphic position	Abundance	Notes	Images
Equisetum	E. sp				Rare in the Hell Creek Formation.
Polypodiaceae?	indeterminate
Salvinia	S. sp				Floating aquatic plant.

Cycadophytes

Genus	Species	Location	Stratigraphic position	Abundance	Notes	Images
Nilssoniocladus	N. comtula				Unlike N. yukonensis, its leaves are pinnatisect pinnules. Common.
	N. yukonensis				The only Hell Creek Formation cycadophyte. A simple leaf. Common.

Ginkgoales

Genus	Species	Location	Stratigraphic position	Abundance	Notes	Images
Ginkgo	G. adiantoides				The only ginkgoalean in the Hell Creek Formation; uncommon

Conifers

Genus	Species	Location	Stratigraphic position	Abundance	Notes	Images
Cupressinocladus	C. interruptus				Casts of cupressaceae foliage. Uncommon
Dammarites	D. sp				A conifer seed cone. It's likely to belong to Elatides longifolia.
Ditaxocladus	D. catenulata				A cupressaceous conifer closely related to Cupressinocladus. Common.
Elatides	E. longifolia				Araucaria-like conifer. Less common in the lower 2/3 but more common in the upper 1/3 of the Hell Creek Formation.[140]
Glyptostrobus	G. europaeus				Uncommon conifer.
Metasequoia	M. occidentalis				M. occidentalis seed cones are known from the Hell Creek.
Sequoia	S. dakotensis[144]				A sequoia known from cones
Platyspiroxylon	Platyspiroxylon sp.[140]				A cupressaceaeous wood morphogenus
Podocarpoxylon	Podocarpoxylon sp.[140]				A possibly podocarpaceous wood morphogenus
Sequoiaxylon	Sequoiaxylon sp.[140]				A cupressaceaeous wood morphogenus
Taxodioxylon	Taxodioxylon sp.[140]				A cupressaceaeous wood morphogenus
Taxodium	T. olrikii				Related to today's bald cypress.

Angiosperms

Genus	Species	Location	Stratigraphic position	Abundance	Notes	Images
"Artocarpus"	"A." lessigiana				Abundant at Brownie Butte, Montana.
Annona?	A?. robusta				Abundant at Brownie Butte, Montana.
Araliaephyllum	A. polevoi				A lobed leaf. Closely relating to Bisonia. Fairly common.
Averrhoites	cf. A. affinis				An uncommon taxon with compound leaves.
Bisonia	B. niemi				A broad leaf, probably in the Laurales. A common taxon. Type specimen was found in South Dakota.
Browniea	B. serrata				In the Nyssaceae, closely relating to extant Camptotheca. Less common.
Cannabaceae?	indeterminate				Incertae sedis. It's not likely in the Cannabaceae.[145]
Carpites	C. ulmiformis				Though this fossil fruit is abundant in the Early Paleocene, it's also found in Hell Creek. It may belong to Apiaceae.[146]
"Celastrus"	"C." taurenensis				Incertae sedis. It's common in the lowermost to the middle Hell Creek Formation, but less common in the upper 1/3 Hell Creek Formation.[140]
"Cinnamomum"	"C." lineafolia				Included in Ficus affinis by L. Hickey. Belongs in Rhamnaceae (modern buckthorns and Ceanothus).[citation needed] Some other specimens referred to Cinnamomum sezanensis(?) sp.), a real cinnamon bush. Its affinity is questionable.
Cissites	cf. C. acerifolia				This morphotype was first described from the Cenomanian Dakota Group.[139]
	C. insignis				This form represents of the group of Cenomanian leaves from Dakota Formation.[139]
	C. lobata				A lobed leaf with half-naked basal lateral veins. Common in the upper 1/3 of the Hell Creek Formation.
	C. puilasokensis				A palmately lobed leaf with 5 primary veins. Common in the upper 1/3 of the Hell Creek Formation.
Cobbania	C. corrugata				A prehistoric species of water lettuce, previously assigned to the genus Pistia.
	C. hickeyi				Another Cobbania species from pond sediments known as "Licking Leaves."[147]
Cornophyllum	C. newberryi				The majority of leaves are entire-margined but some may develop a few teeth.[139]
"Cypercites"	"C." sp				A reed-type plant.
Dryophyllum	D. subfalcatum				This taxon is extremely common in the Hell Creek Formation, but is rare in Paleocene sediments. It is believed to be in Sabiaceae, closely related to the living Meliosma.[139][148]
	aff. "Dryophyllum" subfalcatum				see above.
	"D." tenneseensis				This taxon is similar to D. subfalcatum]] but with extremely high L/W ratio and craspedodromous venation.[139]
Erlingdorfia	E. montana				Johnson, 1996. In the Platanaceae (related to today's Sycamore). A very common taxon.
"Ficus"	"F." planicostata				Despite the genus name, it's in Lauraceae.
Grewiopsis	G. saportana				Another generic Platanaceae.
Harmsia	H. hydrocotyloidea				Incertae sedis. May be related to lotus. An uncommon taxon.
Humulus?	aff. Humulus sp.				May be related to the extant genus Humulus.
Hydropteris	H. pinnata				Floating aquatic fern
Limnobiophyllum	L. scutatum				Floating aquatic monocot, closely related to Pistia.
Liriodendrites	L. bradacii				Johnson, 1996. In the Magnoliidae: a common taxon.
"Liriodendron"	"L." laramiense				Unlobed leaf. May be related to today's tulip tree (yellow poplar). An uncommon taxon.
Liriodendron	L. sp				Four-lobed leaf. May be related to today's tulip tree (yellow poplar). An uncommon taxon.
Leepierceia	L. preartocarpoides				Incertae sedis but possibly in Proteales. Johnson, 1996.
Laurophyllum	L. wardiana				Large leaves. Closely related to "Dryophyllum" subfalcatum.
"Magnolia"	M. pulchra				Occurs in southern the Wyoming flora, Leo Hickey claims it is found further north in Montana and the Dakotas.[citation needed]
Marmarthia	M. johnsonii				A new Marmarthia species described in Peppe et al. 2007.[149]
	M. pearsonii				Johnson, 1996. In the Lauraceae: a very common taxon.
	M. trivialis				Johnson, 1996. In the Lauraceae: a very common taxon.
"Myrica"	"Myrica" torreyi				Incertae sedis. Not actually a bayberry.
Nelumbo	N. sp				One of the most common aquatic plants in Hell Creek.
Nelumbium	N. montanum				An aquatic angiosperm, closely related to lotus. Uncommon.
Nordenskioldia	N. borealis				A fossil fruit likely to belonging to Zizyphoides flabella.[150]
Paranymphaea	P. hastata				Despite the name, it's not related to extant genus Nymphaea.
Palaeoaster	P. porosia				A papaveraceous with fruits and seeds visually similar to Romneya though it's dubious.[citation needed]
Penosphyllum	P. cordatum				May be related to Sterculioideae. A common taxon.
Platanites	P. marginata				Johnson, 1996. In the Platanaceae. A common taxon.
	P. raynoldsii				An uncommon taxon.
Porosia	P. verrucosa				A fossil fruit that may belong to Rutaceae.[151]
Rhamnica	R. cleburnii				Incertae sedis. A Tetracera look-alike leaf.[139]
Sabalites	S. sp				Coryphoid palm tree. Very common.
Spinifructus	S. antiquus				A fruit seed that may belong to the palm family (Arecaceae), closely related to the genus Astrocaryum.[152]
Trapago	T. angulata				A water caltrop look-alike.
Trochodendroides	T. arctica				A fossil fruit that may belong to Trochodendroides nebrascensis.
	T. ellipticum				A katsura look-alike. An uncommon taxon.
	T. genetrix				A katsura look-alike. A common taxon.
	T. nebrascensis				A very common taxon.
"Vitis"	"V." stantonii				Possibly a member of the Platanaceae rather than Vitaceae[140][153]
"Ziziphus"	"Z." fibrillosus				A common taxon.
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)).
	Z. magnifolia				Another Zinigberopsis species, previously assigned to Canna? magnifolia.
Zizyphoides	Z. flabella				An uncommon taxon.

Palynology

Genus	Species	Location	Stratigraphic position	Abundance	Notes	Images
Abietineaepollenites	Abietineaepollenites foveoreticulatus[154]	Montana			A conifer palynomorph
	Abietineaepollenites microalatus[154]	Montana			A conifer palynomorph
	Abietineaepollenites varius[154]	Montana			A conifer palynomorph
Acanthotriletes	Acanthotriletes levidensis[154]	Montana
Alnipollenites	Alnipollenites verus[154]	Montana
Appendicisporites	Appendicisporites tricornitatus[154]	Montana
Aquilapollenites	Aquilapollenites amplus[154]	Montana
	Aquilapollenites attenuatus
	Aquilapollenites collaris
	Aquilapollenites conatus[154]	Montana
	Aquilapollenites delicatus[154]	Montana
	Aquilapollenites marmarthensis
	Aquilapollenites polaris[154]	Montana
	Aquilapollenites pulvinus[154]	Montana
	Aquilapollenites pyriformis[154]	Montana
	Aquilapollenites quadricretaeus
	Aquilapollenites quadrilobus
	Aquilapollenites reductus[154]	Montana
	Aquilapollenites reticulatus[154]	Montana
	Aquilapollenites senonicus
	Aquilapollenites turbidus
	Aquilapollenites striatus
Azolla	Azolla cretacea[154]	Montana			A mosquito fern palynomorph
Balmeisporites	Balmeisporites sp.
Calamospora	Calamospora mesozoica[154]	Montana
Camarozonosporites	Camarozonosporites heskemensis[154]	Montana
Cicatricosisporites	Cicatricosisporites carlylensis[154]	Montana
	Cicatricosisporites dorogensis[154]	Montana
Cingulatisporites	Cingulatisporites dakotaensis[154]	Montana
	Cingulatisporites scabratus[154]	Montana
Clavatricolpites	Clavatricolpites prolatus[154]	Montana
Concavisporites	Concavisporites rugulatus[154]	Montana
	Concavisporites rugulatus[154]	Montana
Converrucosisporites	Converrucosisporites sp.[154]	Montana
Corylus	Corylus granilabratus[154]	Montana			A hazelnut palynomorph
Cupanieidites	Cupanieidites major[154]	Montana
Cyathidites	Cyathidites foveolatus[154]	Montana			A tree fern palynomorph
	Cyathidites minor[154]	Montana			A tree fern palynomorph
	Cyathidites australis	North Dakota			A tree fern palynomorph
	Cyathidites diaphana	North Dakota[155]			A tree fern palynomorph
Cycadopites	Cycadopites scabratus[154]	Montana
Deltoidospora	Deltoidospora diaphana[154]	Montana
Dicotetradites	Dicotetradites granulatus[154]	Montana
Ephedripites	Ephedripites ovatus[154]	Montana
	Ephedripites undulatus[154]	Montana
Erdtmanipollis	Erdtmanipollis cretaceus[154]	Montana South Dakota
Gleicheniidites	Gleicheniidites excelsus[154]	Montana
	Gleicheniidites senonicus[154]	Montana
Gnetaceaepollenites	Gnetaceaepollenites eocenipites[154]	Montana
Haloragacidites	Haloragacidites quadratus[154]	Montana
Hamulatisporis	Hamulatisporis hamulatis[154]	Montana
Hymenophyllumsporites	Hymenophyllumsporites parvus[154]	Montana			A fern spore palynomorph
	Hymenophyllumsporites pseudomaximus[154]	Montana			A fern spore palynomorph
Ilexpollenites	Ilexpollenites compactus
Inaperturopollenites	Inaperturopollenites rugulatus[154]	Montana
Interpollis	Interpollis cf. I. supplingensis
Kurtzipites	Kurtzipites trispissatus[154]	Montana
	Kurtzipites trispissatus[154]	Montana
Laevigatosporites	Laevigatosporites anomalus[154]	Montana
	Laevigatosporites discordatus[154]	Montana
	Laevigatosporites gracilis[154]	Montana
	Laevigatosporites ovatus[154]	Montana
Liliacidites	Liliacidites variegatus[154]	Montana
	Liliacidites sp.[154]	Montana
Lycopodiumsporites	Lycopodiumsporites austroclavatidites[154]	Montana
Momipites	Momipites circularis[154]	Montana
	Momipites parvus[154]	Montana
Monosulcites	Monosulcites carpentieri[154]	Montana
	Monosulcites crescentus[154]	Montana
	Monosulcites latus[154]	Montana
	Monosulcites tectatus[154]	Montana
	Monosulcites sp.[154]	Montana
Myrtipites	Myrtipites granulatus[154]	Montana
	Myrtipites scabratus[154]	Montana
Nyssapollenites	Nyssapollenites analepticus[154]	Montana
	Nyssapollenites pseudocruciatus[154]	Montana
Osmundacidites	Osmundacidites wellmanii[154]	Montana
Pachysandra	Pachysandra cretaceae[154]	Montana South Dakota
Palmidites	Palmidites maximus[154]	Montana
Peromonolites	Peromonolites granulatus[154]	Montana
Phyllocladidites	Phyllocladidites mawsonii[154]	Montana
	Phyllocladidites ruei[154]	Montana
Podocarpidites	Podocarpidites otagoensis[154]	Montana
Pinuspollenites	Pinuspollenites labdacus	North Dakota			A pine palynomorph showing evidence of the genus Pinus in Hell Creek.[155]
	Pinuspollenites sp	North Dakota			A pine palynomorph showing evidence of the genus Pinus in Hell Creek.[155]
Piceapollis	Piceapollis sp	North Dakota[155]			A spruce palynomorph
Polyadopollenites	Polyadopollenites psilatus[154]	Montana
Polycolpites	Polycolpites granulatus[154]	Montana
Polypodiidites	Polypodiidites inangahuensis[154]	Montana
Proteacidites	Proteacidites retusus[154]	Montana
	Proteacidites retusus[154]	Montana
	Proteacidites thalmannii[154]	Montana
Psilatricolporites	Psilatricolporites prolatus[154]	Montana
Pterocaryapollenites	Pterocaryapollenites stellatus[154]	Montana
Reticuloidosporites	Reticuloidosporites dentatus[154]	Montana
Schizosporis	Schizosporis complexus[154]	Montana
	Schizosporis parvus[154]	Montana
Spheripollenites	Spheripollenites subgranulatus[154]	Montana
Spinamonoporites	Spinamonoporites typicus[154]	Montana
Stereisporites	Stereisporites antiquasporites[154]	Montana
	Stereisporites psilatus[154]	Montana
Striainaperturites	Striainaperturites ovatus[154]	Montana
Styx	Styx major[154]	Montana
	Styx minor[154]	Montana
Taxodiaceaepollenites	Taxodiaceaepollenites hiatus[154]	Montana
Triatriopollenites	Triatriopollenites granilabratus[154]	Montana
Tricolpites	Tricolpites bacustriatus[154]	Montana
	Tricolpites delicatulus[154]	Montana
	Tricolpites foveolatus[154]	Montana
	Tricolpites interangulus
	Tricolpites parvistriatus[154]	Montana
	Tricolpites psilascabratus[154]	Montana
	Tricolpites reticulatus[154]	Montana
	Tricolpites striatus[154]	Montana
Tricolpopollenites	Tricolpopollenites clavireticulatus[154]	Montana
	Tricolpopollenites megaexactus[154]	Montana
	Tricolpopollenites microreticulatus[154]	Montana
	Tricolpopollenites microscabratus[154]	Montana
	Tricolpopollenites sp1, sp2[154]	Montana
Tricolporopollenites	Tricolporopollenites elongatus[154]	Montana
	Tricolporopollenites foveotectatus[154]	Montana
	Tricolporopollenites granustriatus[154]	Montana
	Tricolporopollenites megaexactus[154]	Montana
	Tricolporopollenites prolatus[154]	Montana
	Tricolporopollenites striatus[154]	Montana
Triplanosporites	Triplanosporites sinuosus[154]	Montana
Triporopollenites	Triporopollenites rugatus[154]	Montana
Ulmipollenites	Ulmipollenites undulosus[154]	Montana
	Ulmipollenites verrucatus[154]	Montana
Ulmoideipites	Ulmoideipites tricostatus[154]	Montana
Wodehouseia	Wodehouseia spinata[154]	Montana
Zlivisporis	Zlivisporis blanensis[154]	Montana

See also

• List of fossil sites (with link directory)
• Lists of dinosaur-bearing stratigraphic units
• Paleobiota of the Morrison Formation
• Lance fauna
• Cretaceous-Paleogene formations
  • Tremp Formation, Spain
  • Tremp Formation, Spain
  • Lefipán Formation, Argentina
  • Lopez de Bertodano Formation, Antarctica