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. Fossils found in the Hell Creek Formation and the Fort Union Formation of these insects went extinct during the K-T Event.
Genus Species Location Stratigraphic position Material Notes Images Cephaloleichnites Cephaloleichnites strongi Possible hispine beetle herbivory on Zingiberopsis attenuta ?Hemiphlebiidae indet.Indeterminate Possible Hemiphlebiid damselflies Brachycera indet.Indeterminate Undescribed brachyceran flies Nematocera indet.Indeterminate Undescribed nematoceran flies Aeschnidiidae indet.Indeterminate Indeterminate aeschnidiid dragonflies
Molluscs Genus Species Location Stratigraphic position Material Notes Images PlesielliptioP. postbiplicatus Freshwater Unionid river mussels P. gibbosoides Freshwater Unionid river musselsP. whitfieldiFreshwater Unionid river mussels Rhabdotophorus R. aldrichi Freshwater mussel of family Unionidae. Pleurobema P. cryptorhynchus Freshwater mussel of family Unionidae. Plethobasus P. aesopiformis Freshwater mussel of family Unionidae. P. biesopoides Quadrula Q. cylindricoides Freshwater mussel of family Unionidae. Proparreysia P. verrucosiformis Freshwater mussel of family Unionidae. 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
Genus Species Location Stratigraphic position Material Notes ImagesAnura indet.Pearson et al. (2002) p. 154indeterminate North DakotaPearson et al. (2002) pp. 145–167 South DakotaMiddle to upper Hell Creek FormationPearson et al. (2002) p. 1553 unassigned specimensPearson et al. (2002) pp. 156Anura indet. consists of material not currently assigned to any genus of frog.BarbourulaListed as "cf. Barbourula sp." in "Class Amphibia," Estes and Berberian, (1970). Page 4.Indeterminate"Class Amphibia," in Estes and Berberian, (1970). Page 4. Montana"Class Amphibia," in Estes and Berberian, (1970). Page 4. All taxa listed occur in Montana, see page 1.Caudata indet.indeterminate North Dakota South DakotaLower to uppermost Hell Creek Formation149 unassigned specimensMaterial of Caudata indet. is not currently assigned to any genus.EopelobatesListed as "Eopelobates? sp." in "Class Amphibia," Estes and Berberian, (1970). Page 4.Indeterminate MontanaHabrosaurusH. dilatus Montana North Dakota South DakotaMiddle to upper Hell Creek Formation6 specimensHabrosaurus is a sirenid amphibian.LisserpetonL. bairdi MontanaOpisthotritonO. kayi Montana North Dakota South DakotaLower to upper Hell Creek Formation22 specimensOpisthotriton is classified as a Batrachosauroididae.ParanecturusP. garbanii MontanaA member of Proteidae.ProamphiumaP. cretacica MontanaProdesmodonP. copei MontanaScapherpetonS. tectum Montana North Dakota South DakotaLower to upper Hell Creek Formation144 specimensScapherpeton is a scapherpetonid that is very common in the Hell Creek Formation.ScotiophryneS. pustulosa MontanaA small frog
Fish
Bony fish Bony fishes Genus Species Location Stratigraphic position Material Notes Images Acipenser"Class Osteichthyes," in Estes and Berberian, (1970). Page 3. A. amnisinferos North Dakota (Tanis) A sturgeon A. eruciferus Montana"Class Osteichthyes," in Estes and Berberian, (1970). Page 3. All taxa listed occur in Montana, see page 1. A. praeparatorum North Dakota (Tanis) A. cf. A. amnisinferos North Dakota (Tanis) cf. A. sp. North Dakota South DakotaLower to upper Hell Creek Formation18 specimens are tentatively assigned to Acipenser sp.Acipenser sp. is tentatively referred to the genus.AcronichthysA. sp. MontanaVertebral centraAn early otophysan. Originally treated as Otophysi indet. Anchiacipenser A. acanthaspis Montana A sturgeon, originally considered as indeterminate material ?ArotusA. hieroglyphus MontanaA holostean of uncertain affinities. Presence in this formation not certain, and likely uncommon or highly restricted if it is. 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"Class Osteichthyes," in Estes and Berberian, (1970). Page 4. C. amnicolus Montana CyclurusC. fragosus Montana North Dakota South DakotaA small amiid fish (ubiquitous). Previously known as Amia fragosa or Kindleia fragosa. 2610 specimens have been assigned to Kindleia, making it an extremely common genus. "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. Nomen dubium. 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 ParalbulaListed as "cf. Paralbula casei" in "Class Osteichthyes," Estes and Berberian, (1970). Page 4. P. casei Montana"Class Osteichthyes," in Estes and Berberian, (1970). Page 4. All taxa listed occur in Montana, see page 1. Parapsephurus P. willybemisi North Dakota (Tanis) A paddlefish Platacodon P. nanus Montana Small teleost fish Protamia Indeterminate Montana Pachyrhizodontoidei indet. Indeterminate Fish Polyodontidae indet. Indeterminate Montana Paddlefish Protoscaphirhynchus P. squamosus Montana A sturgeon Pugiopsephurus P. inundatus North Dakota (Tanis) A paddlefish
Cartilaginous fish
Chondrichthyes reported from the Hell Creek Formation Genus Species Location Stratigraphic position Material Notes ImagesChiloscylliumC. sp. MontanaA member of Hemiscylliidae.GalagadonG. nordquistae South DakotaIsolated teethA carpet sharkLonchidion"Class Chondrichthyes," in Estes and Berberian, (1970). Page 3.L. selachos Montana"Class Chondrichthyes," in Estes and Berberian, (1970). Page 3. All taxa listed occur in Montana, see page 1. North Dakota South DakotaLower to upper Hell Creek Formation40 specimensA genus of prehistoric sharks in the family Hybodontidae. It makes up 0.4% of the remains of the vertebrates of the Hell Creek Formation.MyledaphusM. pustulosus Montana North Dakota South DakotaLower 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.ProtoginglymostomaP. estesi MontanaA member of Ginglymostomatidae. Formerly assigned to the genus Brachaelurus.RestesiaR. americana Montana North Dakota South DakotaMiddle Hell Creek Formation5 specimens previously assigned to SquatirhinaA 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 DakotaAn isolated tooth.ScapanorhynchusS.sp. North DakotaA Goblin shark relative that lived in shallow water to possibly even brackish and freshwater.CarchariasC.sp North DakotaA sand tiger shark
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.
Ceratopsidae 61% Hadrosauridae 23% Ornithomimidae 5% Tyrannosauridae 4% Hypsilophodontidae 3% Dromaeosauridae 2% Pachycephalosauridae 1% Ankylosauridae 1% Troodontidae 1% (represented only by teeth)
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. 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.
Ornithischians
Ankylosaurs Indeterminate nodosaur remains have been unearthed in the Hell Creek Formation and other nearby areas.