Paleobiota of the Hell Creek Formation facts for kids

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

Invertebrates

Insects like Diptera, Zygopteran, and possibly hemiphlebiid damselflies have been unearthed in Hell Creek in amber. Fossils found in the Hell Creek Formation and the Fort Union Formation of these insects went extinct during the K-T Event.

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

Fish

Bony fish

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

Cartilaginous fish

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

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%
Pachycephalosauridae 1%
Troodontidae 1% (represented only by teeth)

Pie chart of the time averaged census for large-bodied dinosaurs from the entire Hell Creek Formation in the study area.

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

The dinosaurs Thescelosaurus, Ornithomimus, Pachycephalosaurus and Ankylosaurus were also included in the breakdown, but were relatively rare. Other dinosaurs, such as Sphaerotholus, Denversaurus, Torosaurus, Struthiomimus, Acheroraptor, Dakotaraptor, Pectinodon, Richardoestesia, Paronychodon, Anzu, Leptorhynchos and Troodon (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.

Ornithischians

Ankylosaurs

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

Pachycephalosaurs

An undescribed Pachycephalosaur is present in North Dakota. Pachycephalosaur remains have been unearthed in Montana as in the case of the now invalid genus Stenotholus kohleri which is now a junior synonym of Pachycephalosaurus.

Pachycephalosaurs reported from the Hell Creek Formation
Genus	Species	State	Stratigraphic position	Material	Notes	Images
Dracorex	D. hogwartsia	South Dakota	Middle		A pachycephalosaur, possibly synonymous with Pachycephalosaurus.
Pachycephalosaurus	P. wyomingensis	Montana South Dakota			A pachycephalosaur. Also found in the Lance Formation.
Sphaerotholus	S. buchholtzae	Montana	Upper	"Skull material."	A pachycephalosaur whose remains have been found in the Frenchman Formation, Kirtland Formation, and the Horseshoe Canyon Formation.
Stygimoloch	S. spinifer	Montana 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. 8.31% of all vertebrate remains from the Hell Creek Formation are unassigned ceratopsids. 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.

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	L. gracilis		Montana			A small primitive-looking ceratopsian. Fossils have also been found in the Lance Formation in Wyoming.
Tatankaceratops	T. sacrisonorum		South Dakota			A ceratopsian possibly synonymous with Triceratops
Torosaurus	T. latus		Montana North Dakota South Dakota	Upper Hell Creek Formation		A ceratopsian possibly synonymous with Triceratops. A rare ceratopsid. Fossils have been in the Lance Formation, Javelina Formation, North Horn Formation, Laramie Formation and El Picacho Formation.
Triceratops	T. horridus	T. serratus Ugrosaurus olsoni	Montana North Dakota Wyoming South Dakota	Lowermost to the middle Hell Creek Formation	Four specimens are assigned to Triceratops horridus from the Hell Creek Formation. 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. Also found in the Evanston, Frenchman, Lance, Laramie, and Scollard Formations.
Triceratops	T. prorsus		Montana South Dakota	Upper 1/3 of the Hell Creek Formation	Very common. 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.

Ornithopods and Thescelosaurs reported from the Hell Creek Formation
Genus	Species	Synonyms	State	Stratigraphic position	Material	Notes	Images
Edmontosaurus	E. annectens	Anatosaurus annectens Anatotitan copei	Montana South Dakota North Dakota(Mummy Fossil)		Very common.	A hadrosaur. Also found in the Denver, Frenchman, Lance, Laramie, and Scollard Formations.
Thescelosaurus	T. garbanii	Bugenasaura garbanii	Montana South Dakota
	T. neglectus		North Dakota South Dakota	Lower to upper Hell Creek Formation	50 specimens	A small thescelosaurine. Also found in the Frenchman, Lance, Laramie, and Scollard Formations. Two species are known from Hell Creek; T. negelctus and T. garbanii.

Theropods

Theropod tracks have been found in South Dakota. A second footprint that may have been made by a specimen of Tyrannosaurus was first reported in 2007 by British paleontologist Phil Manning, from the Hell Creek Formation of Montana. This second track measures 72 centimeters (28 in) long, shorter than the track described by Lockley and Hunt. Whether or not the track was made by Tyrannosaurus is unclear, though Tyrannosaurus is the only large theropod known to have existed in the Hell Creek Formation, though in past albertosaurine remains have described here but its most likely that they are the remains of Tyrannosaurus rex. Theropod remains are very common in Hell Creek, some of which belong to indeterminate species on maniraptorans.

Alvarezsaurs

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

Tyrannosaurids

Tyrannosaurids reported from the Hell Creek Formation
Genus	Species	Synonyms	State	Stratigraphic position	Material	Notes	Images
Tyrannosaurus	T. rex	Albertosaurus megagracilis Aublysodon molnari Dinotyrannus megagracilis Nanotyrannus lancensis?	Montana North Dakota South Dakota	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. 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.
Nanotyrannus?	N.lancensis	Stygivenator? Deinodon lancensis Albertosaurus lancensis Tyrannosaurus lancensis?	Montana Wyoming	Lower to upper Hell Creek Formation.	A few specimens are known	Invalid genus, now recognised a juvenile T. rex.

Ornithomimosaurs

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

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		One partial skeleton.	An ornithomimid. Numem nudum
Struthiomimus	S. sedens	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.
Ornithomimus	O. velox	Montana South Dakota North Dakota		Fragmentary specimens	A 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 1997, paleontologists discovered a fossil trackway of gigantic oviraptorid belonging to a creature dubbed Wakinyatanka styxi. In the past, oviraptorosaur fossils found were thought to have belonged to Caenagnathus, Chirostenotes, and Elmisaurus. In 2016, an undescribed large-bodied caenagnathid was unearthed in Montana.

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	A. wyliei	North Dakota South Dakota	Lower to upper Hell Creek Formation	12 well-preserved specimens	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.
Caenagnathidae	Indeterminate	Montana			Similar to Citipes and Elmisaurus.

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 disproved in a 2015 study, DePalma et al., when they described the new genus Dakotaraptor, a large species of dromaeosaur. 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 and Saurornitholestes 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	A. temertyorum	Montana North Dakota? South Dakota?	Lower? to upper Hell Creek Formation	ROM 63777, a maxilla and tooth ROM 63778, a partial dentary isolated teeth	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.
Avisaurus	A. archibaldi	Montana	Middle Hell Creek Formation	UCMP 117600, holotype, a tarsometatarsus PU 17324, a tarsometatarsus	An avisaurid.
	cf. A. archibaldi	Montana	Uppermost Hell Creek Formation	YPM 57235, a coracoid	An avisaurid tentatively referred to A. archibaldi based on its size.
	A. sp.	Montana		distal tarsals, metatarsus (juvenile)
Brodavis	B. baileyi	South Dakota		UNSM 50665, a left tarsometatarsus missing proximal end, trochleae II and III.	A primitive hesperornithiform.
Dakotaraptor	D. steini	South Dakota	Upper Hell Creek Formation	PBMNH.P.10.113.T, a partial skeleton. PBMNH.P.10.115.T, a tibia. PBMNH.P.10.118.T, an astragalocalcaneum. isolated teeth.	A dromaeosaurid. Second-largest dromaeosaurid known.
Paronychodon	P. caperatus	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	P. bakkeri	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	P. skutchi	Montana		UCMP 117605, a tarsometatarsus	A hesperornithiform also found in the Lance Formation.
Richardoestesia	R. sp.	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.
"Unnamed enantiornithine B"	Unnamed	Montana		YPM 57823, a partial coracoid	An unnamed enantiornithean.
"Unnamed hesperornithiform A"	Unnamed	Montana		UCMP 13355, a tarsometatarsus	A primitive hesperornithiform. The Hell Creek specimen was referred to the same unnamed taxon as RSM P 2315.1 from the Canadian Frenchman Formation. RSM P 2315.1 was later made the holotype of Brodavis americanus. May be a synonym of Potamornis.
"Unnamed ornithurine B"	Unnamed	Montana		UCMP 129143, a partial coracoid	An ornithurine possibly similar to Cimolopteryx
"Unnamed ornithurine C"	Unnamed	Montana South Dakota		SDSM 64281A, a partial coracoid SDSM 64281B, a partial coracoid UCMP 175251, a partial coracoid MOR 2918, a partial coracoid	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
"Unnamed ornithurine D"	Unnamed	Montana		UCMP 187207, a partial coracoid	An ichthyornithean also present in the Frenchman Formation

Pterosaurs

Indeterminate azhdarchid remains, most likely belong to Quetzalcoatlus or an unidentified genus, have been found in Hell Creek as well as the Javelina Formation and the Ojo Alamo Formation. Inteterminate pteranodontid remains have also been found here as well.

Pterosaurs of the Hell Creek Formation
Taxa	Species	State	Stratigraphic location	Material	Notes	Images
Azhdarchidae spp.	Indeterminate	Montana North Dakota			Records of pterosaur remains from the Hell Creek Formation are two indeterminate specimens, which have been recorded from North Dakota but not described (Johnson et al., 2000; Pearson et al., 2002). A single azhdarchid neck bone may belong to the genus Quetzalcoatlus, though they are not diagnostic to the generic level.
Pterosaur spp.	Indeterminate	South Dakota

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	B. sternbergii	Montana North Dakota South Dakota			Extinct genus of crocodylians that lived from the Late Cretaceous to the Eocene in North America.
Brachychampsa	B. montana	Montana South Dakota North Dakota			Extinct genus of alligatoroid.
Thoracosaurus	T. neocesariensis	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	Indeterminate	Montana			Extinct genus of aquatic turtles belonging to the family Adocidae.
Axestemys	A. infernalis	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.
Compsemys	C. victa	Montana			A relative of Dermatemydidae.
Peckemys	P. brinkman	Montana North Dakota			A relative of Baenidae.
Emarginachelys	E. cretacea	Montana			A relative of chelydrids.
Eubaena	E. cephalica	Montana			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	H. clark	North Dakota			A kinosternoid related to the Central American river turtle.
Plastomenus	P. sp				Trionychidae turtle.
Basilemys	B. sinuosa				Largest dermatemydid land tortoise.
Trionyx	Indeterminate	Montana			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	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	C. monstrosus	Montana			A platynotan lizard of uncertain phylogenetic placement, also known from the Lance Formation.
Cerberophis	C. robustus	Montana			An alethinophidian snake of uncertain phylogenetic placement.
Obamadon	O. gracilis	Montana			A polyglyphanodontian lizard of uncertain phylogenetic placement. Also known from the Lance Formation.
Peneteius	P. aquilonius	Montana			A chamopsiid polyglyphanodontian lizard.
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	C. sp.	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	C. minor	Montana			A multituberculate of uncertain phylogenetic placement.
Cimolodon	C. nitidus	Montana North Dakota			A cimolodontid multituberculate.
	C. cf. nitidus	South Dakota			A cimolodontid multituberculate.
	C. sp.	North Dakota			A cimolodontid multituberculate.
Cimolomys	C. gracilis	Montana			A cimolodontid multituberculate.
Cimolomys	C. cf. gracilis	South Dakota			A cimolomyid multituberculate.
Essonodon	E. browni	Montana			A cimolomyid multituberculate.
Meniscoessus	M. conquistus	South Dakota			A cimolomyid multituberculate.
	M. robustus	Montana North Dakota South Dakota			A cimolomyid multituberculate.
	M. cf. robustus	South Dakota			A cimolomyid multituberculate.
	M. sp.	North Dakota			A cimolomyid multituberculate.
	?M. sp.	North Dakota			A cimolomyid multituberculate.
Mesodma	M. formosa	Montana South Dakota			A neoplagiaulacid multituberculate.
	M. cf. formosa	Montana			A neoplagiaulacid multituberculate.
	M. hensleighi	Montana South Dakota			A neoplagiaulacid multituberculate.
	M. cf. hensleighi	South Dakota			A neoplagiaulacid multituberculate.
	M. thompsoni	Montana North Dakota South Dakota			A neoplagiaulacid multituberculate.
	M. cf. thompsoni	Montana			A neoplagiaulacid multituberculate.
	M sp.	Montana			A neoplagiaulacid multituberculate.
	?M sp.	Montana			A neoplagiaulacid multituberculate.
?Neoplagiaulax	?N. burgessi	Montana			A neoplagiaulacid multituberculate.
Paracimexomys	P. priscus	Montana			A multituberculate of uncertain phylogenetic placement.
Paressonodon	P. nelsoni				A cimolomyid multituberculate.
Stygimys	S. kuszmauli	Montana			It was a member of the extinct order Multituberculata.

Metatherians

Color key

Taxon	Reclassified taxon	Taxon falsely reported as present	Dubious taxon or junior synonym	Ichnotaxon	Ootaxon	Morphotaxon

Notes
Uncertain or tentative taxa are in small text; ~~crossed out~~ taxa are discredited.

Metatherians reported from the Hell Creek Formation
Genus	Species	State	Stratigraphic position	Material	Notes	Images
Aletridelphys	A. florencae	Montana North Dakota South Dakota			A pediomyid.
Aletridelphys	A. hatcheri	Montana South Dakota			A pediomyid.
Alphadon	A. marshi	Montana North Dakota			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			An alphadontid.
	A. wilsoni	Montana			An alphadontid.
	A. cf. wilsoni	Montana			An alphadontid.
	A. sp.	North Dakota South Dakota			An alphadontid.
Didelphodon	D. padanicus	South Dakota			A stagodontid.
	D. vorax	Montana North Dakota			A stagodontid. genus of Stagodontidae marsupials from the Late Cretaceous of North America.
	D. cf. vorax	South Dakota			A stagodontid.
	D. sp.	North Dakota			A stagodontid.
	cf. D. sp.	North Dakota South Dakota			A stagodontid.
Glasbius	G. twitchelli	Montana			A glasbiid.
Glasbius	G. cf. twitchelli	Montana			A glasbiid.
Leptalestes	L. cooki	Montana			A pediomyid.
Leptalestes	L. krejcii	Montana South Dakota			A pediomyid.
Nanocuris	N. improvida				A deltatheridiid.
Nortedelphys	N. jasoni (= N. intermedius)	Montana South Dakota			A herpetotheriid.
Pediomys	P. elegans	Montana South Dakota			A pediomyid.
Protalphadon	P. foxi	Montana			An alphadontid.
Protalphadon	P. lulli	Montana			An alphadontid.
Turgidodon	T. rhaister	Montana			An alphadontid.

Eutherians

Color key

Taxon	Reclassified taxon	Taxon falsely reported as present	Dubious taxon or junior synonym	Ichnotaxon	Ootaxon	Morphotaxon

Notes
Uncertain or tentative taxa are in small text; ~~crossed out~~ taxa are discredited.

Eutherians reported from the Hell Creek Formation
Genus	Species	State	Stratigraphic position	Material	Notes	Images
Altacreodus	A. magnus	Montana North Dakota			a possibe creodont, formerly a species of Cimolestes
Alostera	A. saskatchewanensis	Montana			A eutherian of uncertain phylogenetic placement.
Ambilestes	A. cerberoides	Montana			A eutherian of uncertain classification, formally a species of Cimolestes
Batodon	B. tenuis	Montana			A cimolestid eutherian.
Cimolestes	C. incisus	Montana			A cimolestid eutherian.
Cimolestes	C. stirtoni	Montana			A cimolestid eutherian.
Gypsonictops	G. hypoconus	Montana South Dakota			A gypsonictopsid eutherian.
	G. illuminatus	Montana North Dakota			A gypsonictopsid eutherian.
	G. cf. illuminatus	Montana			A gypsonictopsid eutherian.
	G. sp.	Montana			A gypsonictopsid eutherian.
cf. Paranyctoides	cf. Paranyctoides sp.	Montana			A nyctitheriid eutherian.
Protungulatum	P. coombsi	Montana			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

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

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

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

Dr. Kirk Johnson 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 from Hell Creek
Cycads are found in Hell Creek
Ginkgo (uncommon) are found in Hell Creek
Various angiosperms from Hell Creek

Monkey-puzzle leaves are found in Hell Creek
Fossil palm trees indicate a hotter paleoclimate
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

Plants 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

Baiera
Ginkgo adiantoides

Angiosperms

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

Color key

Taxon	Reclassified taxon	Taxon falsely reported as present	Dubious taxon or junior synonym	Ichnotaxon	Ootaxon	Morphotaxon

Notes
Uncertain or tentative taxa are in small text; ~~crossed out~~ taxa are discredited.

Flora of the Hell Creek Formation
Genus	Species	Location	Stratigraphic position	Abundance	Notes	Images
Aquilapollenites	"Aquilapollenites" attenuatus
	"Aquilapollenites" collaris
	"Aquilapollenites" conatus
	"Aquilapollenites" delicatus
	"Aquilapollenites" marmarthensis
	"Aquilapollenites" quadricretaeus
	"Aquilapollenites" quadrilobus
	"Aquilapollenites" reductus
	"Aquilapollenites" senonicus
	"Aquilapollenites" turbidus
	"Aquilapollenites" striatus
Alnipollenites
"Ficus"	"Ficus" planicostata
	"Ficus" artocarpoides
	"Ficus" trinervis
Ilexpollenites	Ilexpollenites compactus
Interpollis	Interpollis cf. I. supplingensis
Balmeisporites	Balmeisporites sp.
Marmarthia	Marmarthia pearsonii
"Myrica"	"Myrica" torreyi
Platanites	Platanites marginata
Sabalites	Sabalites sp.
Tricolpites	Tricolpites interangulus
Metasequoia	M. sp				Casts of Dawn Redwood seed cones are known from the Hell Creek.
"Grewiopsis"	"G" saportana				Another generic Hamamelididae.
Annona?	A?. robusta				Abundant at Brownie Butte, Montana.
Cobbania	C. corrugata				A prehistoric species of water lettuce, previously assigned to the genus Pistia.
Araucaria	A. araucana				Casts of Monkey-puzzle leaves are found in Hell Creek.
Artocarpus	A. lessigiana				Abundant at Brownie Butte, Montana.
Celastrus	C. taurenensis				Some may be Eucommiacaea.
Cinnamomum	C. lineafolia				Included in Ficus affinis by L. Hickey. Belongs in Rhamnaceae (modern buckthorns and Ceanothus). Some other specimens referred to Cinnamomum sezanensis(?) sp.), a real cinnamon bush.
Cissu	C. marginata				Also spelled "marginatus".
Juglans	J. leconteana
Liriodendrites	L. bradacci				Johnson, 1996. In the Magnoliidae: a common taxon.
Liriodendron	L. laramiense				May be related to today's tulip tree (yellow poplar).
Leepiesceia	L. presrtocarpoides				another laurel.
Marmarthia	M. pearsonii				Johnson, 1996. In the Lauraceae: a common taxon.
Marmarthia	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.
Dombeyopsis	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	indeterminate
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
Glyptostrobus	G. sp
Laurophyllum	L. wardiana
Magnolia	M. pulchra				This species was thought to occur only in southern Wyoming flora, but Leo Hickey claims it is found further north in Montana and the Dakotas.
Marchantia	M. pealii
Nilssonia	N. yukonensis				The only Hell Creek Formation cycadeoid. Uncommon.
Onoclea	O. hesperia
Paranymphaea	P. hastata
Platanophyllum	P. montanum
Porosia	P. verrucosa
Rhamnus	R. salicifolius				Another buckthorn look-alike. Abundant at Brownie Butte, Montana
Sabalites	S. sp				Palm tree.
Sapindopsis	S. powelliana
Sequoites	S. artus				Sequoia tree.
Taxodium	T. olrikii				Related to today's bald cypress.
Trochodendroides	T. arctica
Trochodendroides	T. nebrascensis
Zingiberopsis	Z. attenuata				Related to today's ginger plant. Its closest living relative is the Asian genus Alpinia. Some Hell Creek Formation specimens show damage from hispine beetles ("leaf beetles" (Wilf et al., 2000)).
Dryophyllum	D. subfalcatum				One of the most common plant taxa in the Hell Creek and Lance Formations. Common at Brownie Butte, Montana. If it is close to real Dryophyllum, then it is a beech/chestnut-like tree (Fagaceae). It may also be a walnut-like tree (Juglandaceae).
	D. tenneseensis				see above.
	aff. "Dryophyllum" subfalcatum				see above.
Populus	P. nebrascensis
Cocculus	cf. C. flabella
Cissites	cf. C. acerifolia
Pistia	cf. P. corrugata				Floating aquatic herb.
Palaeoaster	P. inquirenda				A poppy with quite similar seed pods and seeds to that of the extant poppy genus Romneya.

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Paleobiota of the Hell Creek Formation facts for kids

Contents

Invertebrates

Amphibians

Fish

Bony fish

Cartilaginous fish

Dinosaurs

Ornithischians

Ankylosaurs

Pachycephalosaurs

Ceratopsians

Ornithopods and relatives

Theropods

Alvarezsaurs

Tyrannosaurids

Ornithomimosaurs

Oviraptorosaurs

Eumaniraptorans

Pterosaurs

Crocodylomorphs

Turtles

Squamata

Choristoderans

Mammals

Multituberculates

Metatherians

Eutherians

Flora