Hell Creek Formation

The Hell Creek Formation is an intensively-studied division of mostly Upper Cretaceous and some lower Paleocene rocks in North America, named for exposures studied along Hell Creek, near Jordan, Montana. The formation stretches over portions of Montana, North Dakota, South Dakota, and Wyoming. In Montana, the Hell Creek Formation overlies the Fox Hills Formation. The site of Pompeys Pillar National Monument is a small isolated section of the Hell Creek Formation. In 1966, the Hell Creek Fossil Area was designated as a National Natural Landmark by the National Park Service.[1]

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

The world's largest collection of Hell Creek fossils is housed and exhibited at the Museum of the Rockies, in Bozeman, Montana. The specimens displayed are the result of the museum's Hell Creek Project, a joint effort between the museum, Montana State University, the University of Washington,[2] the University of California, Berkeley, the University of North Dakota, and the University of North Carolina which began in 1998.

Hell Creek Formation
Stratigraphic range: MaastrichtianDanian (Lancian)
~66.8–66 Ma
Hell Creek
Exposure in the badlands in the vicinity of Fort Peck Reservoir
TypeGeological formation
Unit ofMontana Group
Sub-unitsBreien, Little Beaver Creek, Middle Sandstone & Pretty Butte Members
UnderliesFort Union Formation
OverliesFox Hills Formation
Lithology
PrimaryClaystone, mudstone
OtherSandstone, siltstone, conglomerate, amber
Location
Coordinates46°54′N 101°30′W / 46.9°N 101.5°WCoordinates: 46°54′N 101°30′W / 46.9°N 101.5°W
Approximate paleocoordinates52°36′N 74°24′W / 52.6°N 74.4°W
RegionMontana, North Dakota,
South Dakota, Wyoming
Country United States
Type section
Named forHell Creek, Jordan, Montana
Paleontological camp
Paleontological camp of Museum of the Rockies in eastern Montana – Hell Creek Formation (summer dig season 2009)

Geology

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

The Hell Creek Formation in Montana overlies the Fox Hills Formation and underlies the Fort Union Formation, and the boundary with the latter occurs near the Cretaceous-Paleogene boundary (K-Pg), which defines the end of the Cretaceous period and has been dated to 66 ± 0.07 Ma old.[3] The 90 metres of deposit was created in about 2 million years.[4] Fauna characteristic of the Hell Creek (Lancian land vertebrate age) are found as high as a few meters below the boundary.[5]

The K-Pg boundary is generally situated near the contact between the upper Hell Creek and the lower Ludlow member of the Fort Union Formation, though in some areas (e.g. in North Dakota) the boundary is well within the Ludlow Member, 3 metres (9.8 ft) above the boundary with the Hell Creek in some areas.[5] On the other hand, in some small regions of Montana, the Hell Creek Formation contains the K-Pg boundary, and extends slightly into the Paleogene.[6]

The Tanis site in North Dakota contains evidence of what is proposed to be a record of the effects of the Chicxulub meteorite impact – such as the chaotic mixing of fossil carcasses and a layer of glass tektites with associated impact impressions – deposited minutes to hours after the impact.[7][8][9]

Paleobiology

Hell Creek Formation Fauna
Hell Creek Fauna

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

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

Depositional environment

Brussels Zonienwoud
The dominant plants of the Hell Creek Formation are mainly flowering plants

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

The Hell Creek Formation, Lance Formation and Scollard Formation represent different sections of the western shore of the shallow sea that divided western and eastern North America during the Cretaceous. Swampy lowlands were the habitat of various animals, including dinosaurs. A broad coastal plain extended westward from the seaway to the newly formed Rocky Mountains. These formations are composed largely of sandstone and mudstone which have been attributed to floodplain, fluvial, lacustrine, swamp, estuarine and coastal plain environments.[10][11][12] Hell Creek is the best studied of these ancient environments. At the time, this region had a subtropical, warm and moist climate. The climate was humid, with flowering plants, conifers, palmettos, and ferns in the swamps, and conifers, canopy, understory plants, ash trees, live oak and shrubs in the forests. In northwestern South Dakota, strips of black layers deposited in the wetland environment are rich in coal, and a bright band-like layer of sand and mud from the river floodplain accumulated. Many plant species were supported, primarily angiosperms, and less commonly conifers, bald cypress, ferns and cycads. An abundance of fossil leaves are found at dozens of different sites indicating that the area was largely forested by small trees.

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.

Fish

Cartilaginous fish

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

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

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

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

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

Fossil footprints of dinosaurs from the Hell Creek Formation are very rare. As of 2017, there is only one find of a possible Tyrannosaurus rex footprint, dating from 2007 and described a year later.[31]

Ornithischians

Pachycephalosaurs

An undescribed Pachycephalosaur is present in North Dakota.[35]

Ceratopsians

Indeterminate ceratopsid specimens are extremely common. 8.31% of all vertebrate remains from the Hell Creek Formation are unassigned ceratopsids.[16] 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.[38][39][40]

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.

Ornithopods and Parksosaurs

Indeterminate hadrosaurid remains are very common in the Hell Creek Formation.[13]

Theropods

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

Theropod tracks have been found in South Dakota.[33] An unnamed alvarezsaurid, closely related to the Asian genus Mononykus, is known from Montana.[49] 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.[50][51]

Ornithomimosaurs

Ornithomimid remains are not uncommon in the Hell Creek Formation.[13] Fifteen specimens from the Hell Creek Formation are undetermined ornithomimids[16]

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

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.[54]

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.

Eumaniraptorans

Historically, numerous teeth have been attributed to various dromaeosaurid and troodontid taxa with known body fossils from only older formations, including Dromaeosaurus, Saurornitholestes, and Troodon. However, in a 2013 study, Evans et al. concluded that there is little evidence for more than a single dromaeosaurid taxon, Acheroraptor, in the Hell Creek-Lance assemblages, which would render these taxa invalid for this formation. This was disproved in a 2015 study, DePalma et al., when they described the new genus Dakotaraptor, a large species of dromaeosaur.[56] Though it should be noted as mentioned earlier that fossilized teeth of various troodontids and coelurosaurs are common throughout the Hell Creek Formation; the best known examples include Paronychodon, Pectinodon and Richardoestesia, respectively.

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.

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.

Lizards and snakes

Color key
Taxon Reclassified taxon Taxon falsely reported as present Dubious taxon or junior synonym Ichnotaxon Ootaxon Morphotaxon
Notes
Uncertain or tentative taxa are in small text; crossed out taxa are discredited.

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.

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.

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.

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.

Flora

Conguillio llaima
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.[79][80] 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.

Spinifructus antiquus fruits 01
Fossil fruits from the Hell Creek Formation of Spinifructus antiquus of the palm family (Arecaceae), closely related to the genus Astrocaryum.

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

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

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

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

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

Ferns from Hell Creek

Cycads

Cycads are found in Hell Creek

Ginko bilboa 'King of Dongting' (Ginkgoaceae) leaves

Ginkgo (uncommon) are found in Hell Creek

Blossoms 2

Various angiosperms from Hell Creek

Araucaria araucana by Scott Zona - 002

Monkey-puzzle leaves are found in Hell Creek

MumbaiClimate

Fossil palm trees indicate a hotter paleoclimate

Esneux AR2JPG

Redwood seed cones are known from Hell Creek

Laurus novocanariensis01

Laurus are found in Hell Creek

Cercidiphyllum japonicum

Cercidiphyllum are found in Hell Creek

Magnolia liliiflora3

Magnolia is commonly found in Hell Creek

Plants of the Hell Creek Formation

Gymnosperms

Ginkgos

Angiosperms

Color key
Taxon Reclassified taxon Taxon falsely reported as present Dubious taxon or junior synonym Ichnotaxon Ootaxon Morphotaxon
Notes
Uncertain or tentative taxa are in small text; crossed out taxa are discredited.

See also

References

  1. ^ "National Natural Landmarks - National Natural Landmarks (U.S. National Park Service)". www.nps.gov. Retrieved 22 March 2019. Year designated: 1966
  2. ^ "Hell Creek Project – Wilson Lab".
  3. ^ Husson, D.; Galbrun, B.; Laskar, J.; Hinnov, L. A.; Thibault, N.; Gardin, S.; Locklair, R. E. (2011). "Astronomical calibration of the Maastrichtian (late Cretaceous)". Earth and Planetary Science Letters. 305 (3): 328–340. Bibcode:2011E&PSL.305..328H. doi:10.1016/j.epsl.2011.03.008.
  4. ^ LeCain, Rebecca (2010). "Magnetostratigraphy of the Hell Creek and lowerFort Union formations in northeast Montana".
  5. ^ a b Pearson, D. A., Schaefer, T., Johnson, K. R., Nichols, D. J., & Hunter, J. P. (2002). Vertebrate biostratigraphy of the Hell Creek Formation in southwestern North Dakota and northwestern South Dakota. Hartman et al, 145–167.
  6. ^ Johnson, K. R., Nichols, D. J., & Hartman, J. H. (2002). Hell Creek Formation: A 2001 synthesis. The Hell Creek Formation and the Cretaceous-Tertiary Boundary in the northern Great Plains: Geological Society of America Special Paper, 361, 503–510.
  7. ^ DePalma RA, Smit J, Burnham DA, Kuiper K, Manning PL, Oleinik A, Larson P, Maurrasse FJ, Vellekoop J, Richards MA, Gurche L, Walter Alvarez W (April 2019). "A seismically induced onshore surge deposit at the KPg boundary, North Dakota". Proceedings of the National Academy of Sciences. 116 (17): 8190–8199. doi:10.1073/pnas.1817407116. PMID 30936306.
  8. ^ Broad, William J.; Chang, Kenneth (29 March 2019). "Fossil Site Reveals Day That Meteor Hit Earth and, Maybe, Wiped Out Dinosaurs". The New York Times. ISSN 0362-4331. Retrieved 1 April 2019.
  9. ^ Douglas Preston (28 March 2019). "The Day the Dinosaurs Died". The New Yorker.
  10. ^ Lofgren, D.F. (1997). "Hell Creek Formation". In: Currie, P.J. & Padian, K., eds. (1997). The Encyclopedia of Dinosaurs. San Diego: Academic Press. pp. 302–303. ISBN 978-0-122-26810-6.CS1 maint: Uses editors parameter (link)
  11. ^ Breithaupt, B.H. (1997). "Lance Formation". In: Currie, P.J. & Padian, K., eds. (1997). The Encyclopedia of Dinosaurs. San Diego: Academic Press. pp. 394–395. ISBN 978-0-122-26810-6.CS1 maint: Uses editors parameter (link)
  12. ^ Eberth, D.A. (1997). "Edmonton Group". In: Currie, P.J. & Padian, K., eds. (1997). The Encyclopedia of Dinosaurs. San Diego: Academic Press. pp. 199–204. ISBN 978-0-122-26810-6.CS1 maint: Uses editors parameter (link)
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  14. ^ a b c d e f g h i j k l m n o p q r s t u v w x y z aa ab ac ad ae af ag ah ai aj Pearson et al. (2002) pp. 145–167
  15. ^ a b c d e f g h i j k l m n o p q r Pearson et al. (2002) p. 155
  16. ^ a b c d e f g h i j k l m n o p q r s Pearson et al. (2002) pp. 156
  17. ^ Listed as "cf. Barbourula sp." in "Class Amphibia," Estes and Berberian, (1970). Page 4.
  18. ^ a b c d e f g h i j k l m n o p "Class Amphibia," in Estes and Berberian, (1970). Page 4.
  19. ^ a b c d e f g h i "Class Amphibia," in Estes and Berberian, (1970). Page 4. All taxa listed occur in Montana, see page 1.
  20. ^ Listed as "Eopelobates? sp." in "Class Amphibia," Estes and Berberian, (1970). Page 4.
  21. ^ a b c d David G. Demar Jr. (2013). "A new fossil salamander (Caudata, Proteidae) from the Upper Cretaceous (Maastrichtian) Hell Creek Formation, Montana, U.S.A". Journal of Vertebrate Paleontology. 33 (3): 588–598. doi:10.1080/02724634.2013.734887.
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  25. ^ a b c "Class Osteichthyes," in Estes and Berberian, (1970). Page 4. All taxa listed occur in Montana, see page 1.
  26. ^ a b Listed as "cf. Paralbula casei" in "Class Osteichthyes," Estes and Berberian, (1970). Page 4.
  27. ^ a b c d e f g h i j k l m n o p q r s Todd D. Cook; Michael G. Newbrey; Donald B. Brinkman; James I. Kirkland (2014). Euselachians from the freshwater deposits of the Hell Creek Formation of Montana. GSA Special Papers. Geological Society of America Special Papers. 503. pp. 229–246. doi:10.1130/2014.2503(08). ISBN 978-0-8137-2503-1.
  28. ^ a b Terry A. Gates; Eric Gorscak; Peter J. Makovicky (2019). "New sharks and other chondrichthyans from the latest Maastrichtian (Late Cretaceous) of North America". Journal of Paleontology. 93 (3): 512–530. doi:10.1017/jpa.2018.92.
  29. ^ a b "Class Chondrichthyes," in Estes and Berberian, (1970). Page 3.
  30. ^ "Class Chondrichthyes," in Estes and Berberian, (1970). Page 3. All taxa listed occur in Montana, see page 1.
  31. ^ Manning, P. L.; Ott, C.; Falkingham, P. L. (2008). "The first tyrannosaurid track from the Hell Creek Formation (Late Cretaceous), Montana, U.S.A". PALAIOS. 23 (10): 645–647. Bibcode:2008Palai..23..645M. doi:10.2110/palo.2008.p08-030r.
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  40. ^ O' Connell, Max. "Dinosaur skull found in Buffalo likely a new species". Rapid City Journal. Retrieved 27 August 2015.
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  42. ^ Scannella, J.; Horner, J.R. (2010). "Torosaurus Marsh, 1891, is Triceratops Marsh, 1889 (Ceratopsidae: Chasmosaurinae): synonymy through ontogeny". Journal of Vertebrate Paleontology. 30 (4): 1157–1168. doi:10.1080/02724634.2010.483632.
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  46. ^ a b Listed as "?Thescelosaurus garbanii" in "Dinosaur distribution (Late Cretaceous; North America; Montana)." Weishampel, et al. (2004). Page 584.
  47. ^ Noted as being present, although misspelled as "Thescelosaurus garbani, in " "Dinosaur distribution (Late Cretaceous; North America; South Dakota)." Weishampel, et al. (2004). Page 586.
  48. ^ Boyd, Brown, et al. (2009)
  49. ^ Hutchinson and Chiappe, 1998. The first known alvarezsaurid (Theropoda: Aves) from North America. Journal of Vertebrate Paleontology. 18(3), 447–450.
  50. ^ Dalman, S.G.; Lucas, S.G. "A new large Tyrannosaurid Alamotyrannus brinkmani, n. gen., n. sp. (Theropoda: Tyrannosauridae), from the Upper Cretaceous Ojo Alamo Formation (Naashoibito Member), San Juan Basin, New Mexico". New Mexico Museum of Natural History and Science Bulletin.
  51. ^ Molnar, R.E. (January 1980). "An Albertosaur from the Hell Creek Formation of Montana". Journal of Paleontology. 54 (1): 102–108. JSTOR 1304167.
  52. ^ Triebold, 1997. The Sandy Site: Small Dinosaurs from the Hell Creek Formation of South Dakota. in Wolberg, Stump and Rosenberg (eds). Dinofest International: Proceedings of a Symposium sponsored by Arizona
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  54. ^ Maltese, Anthony (17 December 2013). "Giant Oviraptor Tracks from the Hell Creek". RMDRC paleo lab. Retrieved 17 December 2013.
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  56. ^ a b c d e f g h i Evans, D. C.; Larson, D. W.; Currie, P. J. (2013). "A new dromaeosaurid (Dinosauria: Theropoda) with Asian affinities from the latest Cretaceous of North America". Naturwissenschaften. 100 (11): 1041–9. Bibcode:2013NW....100.1041E. doi:10.1007/s00114-013-1107-5. PMID 24248432.
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  68. ^ a b c d "Order Testudinata," in Estes and Berberian, (1970). Page 5. All taxa listed occur in Montana, see page 1.
  69. ^ Arbour, V.M.; Zanno, L.E.; Larson, D.W.; Evans, D.C.; Sues, H. (2015). "The furculae of the dromaeosaurid dinosaur Dakotaraptor steini are trionychid turtle entoplastra". PeerJ PrePrints. 3: e1957.
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Bibliography

  • Pearson, D. A.; Schaefer, T.; Johnson, K. R.; Nichols, D. J.; Hunter, J. P. (2002). "Vertebrate Biostratigraphy of the Hell Creek Formation in Southwestern North Dakota and Northwestern South Dakota". In Hartman, John H.; Johnson, Kirk R.; Nichols, Douglas J. (eds.). The Hell Creek Formation and the Cretaceous-Tertiary boundary in the northern Great Plains: An integrated continental record of the end of the Cretaceous. Geological Society of America. pp. 145–167. ISBN 9780813723617. Special Paper 361.
  • Bakker, R. T., Sullivan, R. M., Porter, V., Larson, P. and Saulsbury, S. J. (2006). "Dracorex hogwartsia, n. gen., n. sp., a spiked, flat-headed pachycephalosaurid dinosaur from the Upper Cretaceous Hell Creek Formation of South Dakota". in Lucas, S. G. and Sullivan, R. M., eds., Late Cretaceous vertebrates from the Western Interior. New Mexico Museum of Natural History and Science Bulletin 35, pp. 331–345.
  • Boyd, Clint A.; Brown, Caleb M.; Scheetz, Rodney D.; Clarke; Julia A. (2009). "Taxonomic revision of the basal neornithischian taxa Thescelosaurus and Bugenasaura". Journal of Vertebrate Paleontology. 29 (3): 758–770. doi:10.1671/039.029.0328.
  • Estes, R.; Berberian, P. (1970). "Paleoecology of a late Cretaceous vertebrate community from Montana". Breviora. 343.
  • Henderson, M.D.; Peterson, J.E. (2006). "An azhdarchid pterosaur cervical vertebra from the Hell Creek Formation (Maastrichtian) of southeastern Montana". Journal of Vertebrate Paleontology. 26 (1): 192–195. doi:10.1671/0272-4634(2006)26[192:aapcvf]2.0.co;2.
  • Longrich, N. (2008). "A new, large ornithomimid from the Cretaceous Dinosaur Park Formation of Alberta, Canada: Implications for the study of dissociated dinosaur remains". Palaeontology. 54 (1): 983–996. doi:10.1111/j.1475-4983.2008.00791.x.
  • Varricchio, D. J. 2001. Late Cretaceous oviraptorosaur (Theropoda) dinosaurs from Montana. pp. 42–57 in D. H. Tanke and K. Carpenter (eds.), Mesozoic Vertebrate Life. Indiana University Press, Indianapolis, Indiana.
  • Weishampel, David B.; Dodson, Peter; and Osmólska, Halszka (eds.): The Dinosauria, 2nd, Berkeley: University of California Press. 861 pages. ISBN 0-520-24209-2.

External links

Acheroraptor

Acheroraptor is an extinct genus of dromaeosaurid theropod dinosaur known from the latest Maastrichtian Hell Creek Formation of Montana, United States. It contains a single species, Acheroraptor temertyorum. A. temertyorum is one of the two geologically youngest known species of dromaeosaurids, the other being Dakotaraptor, which is also known from Hell Creek.

Cedrobaena

Cedrobaena is an extinct genus of turtle which existed in the Tiffanian Cedar Point Quarry, Wyoming and in the latest Maastrichtian Hell Creek Formation, United States. It was first named by Tyler R. Lyson and Walter G. Joyce in 2009 and the type species is Cedrobaena putorius.

Chamops

Chamops is an extinct genus of polyglyphanodontian lizard from the Late Cretaceous of North America. Fossils have been found in the Hell Creek Formation of Montana. It is known from only one species, C. segnis.Chamops grew to approximately 0.5 meters (20 inches) long, and 2 kilograms (4 pounds) in weight. Unlike other polyglyphanodonts, Chamops had a more blunt snout. Chamops belonged to the Chamopsiid family of polyglyphanodonian lizards that lived in the Northern Hemisphere during the Late Cretatceous, although there are some possible Chamopsiid genera from South America and the Kem Kem Bone Beds in Morocco. It was originally thought Chamops and kin are related to whiptails, although it is now thought they are more closely related to iguanas.

Dakota (fossil)

Dakota is the nickname given to a fossil Edmontosaurus annectens found in the Hell Creek Formation in North Dakota. It is about 67 million years old, placing it in the Maastrichtian, the last stage of the Cretaceous period. It was about 11 m (35 ft) long and weighed about 3.5 tons.The fossil is unusual and scientifically valuable because soft tissue including skin and muscle have been fossilized, giving researchers the rare opportunity to study more than bones, as with most vertebrate fossils. Preliminary research results indicate that hadrosaurs had heavier tails and were able to run faster than was previously thought.

Dakotaraptor

Dakotaraptor is a genus of large carnivorous dromaeosaurid theropod from the Late Cretaceous of North America.

The first fossils of Dakotaraptor were found in South Dakota, United States, in 2005. In 2015, the genus Dakotaraptor received its name, meaning "plunderer of Dakota", when the type species Dakotaraptor steini was described. The fossils contain an incomplete skeleton without a skull and some individual bones. They have been found in the Maastrichtian-age Hell Creek Formation, dated to the very end of the Cretaceous period, making Dakotaraptor one of the last surviving dromaeosaurids.

Dakotaraptor was about 5.5 metres (18 ft) long, which makes it one of the largest dromaeosaurids known. It had long arms with one of the lower arm bones showing quill knobs, demonstrating that it was most likely feathered. It also had long rear legs with a very large sickle claw on the second toe; this claw could be used to kill relatively large plant-eating dinosaurs. It lived in the same time and area as many iconic late Cretaceous dinosaurs such as Ankylosaurus, Triceratops, and Tyrannosaurus.

Gamerabaena

Gamerabaena is an extinct genus of baenid turtle which existed in North Dakota during the late Cretaceous period. It is known from a single fragmentary skull that was found in the Maastrichtian-age Hell Creek Formation. It contains the species Gamerabaena sonsalla. Gamerabaena is similar to the genus Palatobaena, but it differs in its lack of a posterior expansion of the triturating (or chewing) surface, a somewhat rectangular skull, and a wide angle between the maxillae. Gamerabaena also has a lingual ridge on the inner side of the jaw that is not seen in Palatobaena.Gamerabaena is considered the sister taxon of Palatobaena and shares features with both Palatobaena and Plesiobaena. These features, which include slightly upturned eye sockets, are seen as intermediate between the two other genera. While Gamerabaena is known only from the skull, it may belong to the same species as "Baena" hayi, which is known primarily from the shell.The genus is named after Gamera, a giant flying, fire-breathing turtle from a series of Japanese tokusatsu films.

Gilmoremys

Gilmoremys is an extinct genus of softshell turtle which lived during the late Cretaceous (Maastrichtian stage) of North Dakota, Montana and Wyoming, United States.

Lance Formation

The Lance (Creek) Formation is a division of Late Cretaceous (dating to about 69 - 66 Ma) rocks in the western United States. Named after Lance Creek, Wyoming, the microvertebrate fossils and dinosaurs represent important components of the latest Mesozoic vertebrate faunas. The Lance Formation is Late Maastrichtian in age (Lancian land mammal age), and shares much fauna with the Hell Creek Formation of Montana and North Dakota, the Frenchman Formation of southwest Saskatchewan, and the lower part of the Scollard Formation of Alberta.

The Lance Formation occurs above the Baculites clinolobatus ammonite marine zone in Wyoming, the top of which has been dated to about 69 million years ago, and extends to the K-Pg boundary, 66 million years ago. However, the characteristic land vertebrate fauna of the Lancian age (which take its name from this formation) is only found in the upper strata of the Lance, roughly corresponding to the thinner equivalent formations such as the Hell Creek Formation, the base of which has been estimated at 66.8 million years old.

List of fossiliferous stratigraphic units in Montana

This article contains a list of fossil-bearing stratigraphic units in the state of Montana, U.S.

List of vertebrate fauna of the Maastrichtian stage

This is an incomplete list that briefly describes vertebrates that were extant during the Maastrichtian, a stage of the Late Cretaceous Period which extended from 72.1 to 66 million years before present. This was the last time period in which non-avian dinosaurs, pterosaurs, plesiosaurs, and mosasaurs existed.

Palatobaena

Palatobaena is an extinct genus of baenid turtle. It was first named by Gaffney in 1972 and the type species is Palatobaena bairdi. It based on a fragmentary skull from the Fort Union Formation of the Bighorn Basin of Wyoming. The two other species are P. gaffneyi (a complete skull from Eocene (Wasatchian North American Land Mammal Age)) and P. cohen which existed in Hell Creek Formation, North Dakota during the late Cretaceous period (Maastrichtian age).

Paralbula

Paralbula is an extinct genus of prehistoric bony fish. They can be found in the Hell Creek Formation, in Montana, United States.

Peckemys

Peckemys is an extinct genus of turtle which existed in the Hell Creek Formation, United States during the late Cretaceous period (Maastrichtian age). It was first named by Tyler R. Lyson and Walter G. Joyce in 2009 and the type species is Peckemys brinkman.

Pectinodon

Pectinodon is a genus of dinosaurs from the Late Cretaceous period (66 mya). It currently contains a single valid species, Pectinodon bakkeri (sometimes classified as Troodon bakkeri), known only from teeth.In 1982, Kenneth Carpenter named a number of theropod teeth from the late Maastrichtian Lance Formation of Wyoming as the type species Pectinodon bakkeri. The generic name is derived from Latin pecten, "comb", and Greek ὀδών, odon, "tooth", in reference to the comb-like serrations on the rear edge of the teeth. The specific name honours Robert Thomas Bakker.The holotype, UCM 38445, consists of a 6.2 mm long adult tooth. The paratypes are three juvenile teeth.In 1985 Lev Nesov named a second species, Pectinodon asiamericanus, based on specimen CCMGE 49/12176, a tooth from the Khodzhakul Formation of Uzbekistan dating from the Cenomanian. This is today often considered a nomen dubium.While historically considered synonymous with Troodon or more specifically the species Troodon formosus, Philip Currie and colleagues (1990) noted that the P. bakkeri fossils from the Hell Creek Formation and Lance Formation might belong to different species. In 1991, George Olshevsky assigned the Lance formation fossils to the species Troodon bakkeri. In 2011, Zanno and colleagues reviewed the convoluted history of troodontid classification in Late Cretaceous North America. They followed Longrich (2008) in treating Pectinodon bakkeri as a valid genus, and noted that it is likely the numerous Late Cretaceous specimens currently assigned to Troodon formosus almost certainly represent numerous new species, but that a more thorough review of the specimens is required.In 2013 Currie and Derek Larson concluded that Pectinodon bakkeri was valid and its teeth could be found both in the Lance Formation and the coeval Hell Creek Formation. Some teeth from the older Campanian Dinosaur Park Formation could not be statistically differentiated from them, likely due to an insufficiently large sample, and were referred to a cf. Pectinodon.

Scapherpeton

Scapherpeton is an extinct genus of prehistoric amphibian. Fossils of it have been found in the Hell Creek Formation.

Sphaerium beckmani

Sphaerium beckmani is an extinct species of fossil freshwater pea clams from the Late Cretaceous deposits of North America. This species was first described by the American paleontologist Loris Shano Russell in 1976. The specimens were collected by the American paleontologist Karl M. Waage from 1961 to 1962 from the Hell Creek Formation of eastern Montana. The locality is dated to the late Maastrichtian Age (around 66.0 to 72.1 million years ago).

Stygimoloch

Stygimoloch ("devil from hell," from Styx, Greek mythological underworld river, and moloch, Hebrew for an evil-connoted angel, such as the Angel of Death) is a genus of pachycephalosaurid dinosaur from the end of the Cretaceous period, roughly 66 million years ago. Its taxonomical status is in dispute, as the failure to discover adult specimens strongly implies that collected holotypes merely represent juvenile pachycephalosaurs. This hypothesis has been supported by numerous modern studies, the most recent of which agrees that Stygimoloch is synonymous with Pachycephalosaurus. The genus was discovered in the Hell Creek Formation, Ferris Formation, and Lance Formation of the Western Interior (United States), where it lived alongside such genera as Tyrannosaurus, Triceratops, and Edmontosaurus.

Tatankaceratops

Tatankaceratops (meaning "Bison horn face") is a controversial genus of herbivorous ceratopsian dinosaur. It is a small chasmosaurine ceratopsian which lived during the Late Cretaceous period (latest Maastrichtian stage) in what is now South Dakota. It is known from a single partial skull which was collected from the Hell Creek Formation, dating to 66 million years ago. Tatankaceratops was described by Christopher J. Ott and Peter L. Larson in 2010 and the type species is Tatankaceratops sacrisonorum. Tatankaceratops is known from one specimen housed at the Black Hills Institute, BHI 6226.

In 2011, Nick Longrich published a paper containing a brief re-evaluation of Tatankaceratops. Longrich suggested that Tatankaceratops appeared to possess a bizarre mix of characteristics from adult and juvenile Triceratops specimens. Longrich noted that this animal could represent a dwarf Triceratops species or simply a Triceratops specimen with a developmental disorder which caused it to stop growing prematurely. Other paleontologists, including Thomas R. Holtz, Jr., have written that they "strongly suspect" Tatankaceratops is merely a juvenile specimen of Triceratops.

Triceratops

Triceratops is a genus of herbivorous ceratopsid dinosaur that first appeared during the late Maastrichtian stage of the late Cretaceous period, about 68 million years ago (mya) in what is now North America. It is one of the last known non-avian dinosaur genera, and became extinct in the Cretaceous–Paleogene extinction event 66 million years ago. The name Triceratops, which literally means "three-horned face", is derived from the Ancient Greek words τρί- (tri-) meaning "three", κέρας (kéras) meaning "horn", and ὤψ (ōps) meaning "face".

Triceratops has been documented by numerous remains collected since the genus was first described in 1889 by Othniel Charles Marsh. Specimens representing life stages from hatchling to adult have been found. As the archetypal ceratopsid, Triceratops is one of the most popular dinosaurs, and has been featured in film, postal stamps, and many other types of media.

Bearing a large bony frill and three horns on the skull, and its large four-legged body possessing similarities with the modern rhinoceros, Triceratops is one of the most recognizable of all dinosaurs and the best known ceratopsid. It was also one of the largest, up to nine metres long and twelve tonnes in weight. It shared the landscape with and was probably preyed upon by Tyrannosaurus, though it is less certain that the two did battle in the manner often depicted in museum displays and popular images. The functions of the frills and three distinctive facial horns on its head have long inspired debate. Traditionally, these have been viewed as defensive weapons against predators. More recent interpretations find it probable that these features were primarily used in species identification, courtship and dominance display, much like the antlers and horns of modern species.

Triceratops was traditionally placed within the "short-frilled" ceratopsids but modern cladistic studies show it to be a member of the Chasmosaurinae which usually have long frills. Two species, T. horridus and T. prorsus, are considered valid today, from the seventeen species that have ever been named. Research published in 2010 concluded that the contemporaneous Torosaurus, a ceratopsid long regarded as a separate genus, represents Triceratops in its mature form. This view was immediately disputed with examination of more fossil evidence needed to settle the debate.

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

Plesielliptio

P. postbiplicatus

Fresh water Pelecypod.

P. gibbosoides

P. whitfieldi

Rhabdotophorus

R. aldrichi

Pleurobema

P. cryptorhynchus

Plethobasus

P. aesopiformis

P. biesopoides

Quadrula

Q. cylindricoides

Proparreysia

P. verrucosiformis

P. holmesiana

P. barnumi

P. percorrugata

P. pyramidatoides

P. letsoni

P. retusoides

P. corbiculoides

P. paucinodosa

Obovaria?

O?. pyramidella

Corbicula

C. cf. subelliptica

C. sp

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

Sphaerium

S. beckmani

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

Freshwater Fingernail Clam

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

Anura (frog)[13]

indeterminate[13]

Middle to upper Hell Creek Formation[15]

3 unassigned specimens[16]

Anura indet. consists of material not currently assigned to any genus of frog.[13]

Barbourula[17]

Indeterminate[18]

Caudata (salamander)[13]

indeterminate[13]

Lower to uppermost Hell Creek Formation[15]

149 unassigned specimens[16]

Material of Caudata indet. is not currently assigned to any genus.[13]

Eopelobates[20]

Indeterminate[18]

Habrosaurus[13][18]

H. dilatus[13][18]

Middle to upper Hell Creek Formation[15]

6 specimens[16]

Habrosaurus is a sirenid amphibian.[13]

Lisserpeton[18]

L. bairdi[18]

Opisthotriton[13][18]

O. kayi[13][18]

Lower to upper Hell Creek Formation[15]

22 specimens[16]

Opisthotriton is classified as a Batrachosauroididae.[13]

Paranecturus[21]

P. garbanii[21]

A member of Proteidae.[21]

Proamphiuma[18]

P. cretacica[18]

Prodesmodon[18]

P. copei[18]

Scapherpeton[13][18]

S. tectum[13][18]

Lower to upper Hell Creek Formation[15]

144 specimens[16]

Scapherpeton is a scapherpetonid that is very common in the Hell Creek Formation.[13]

Scotiophryne[18]

S. pustulosa[18]

A small frog

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

Acipenser[13][22]

A. eruciferus[22]

A sturgeon

cf. A. sp.[13]

Lower to upper Hell Creek Formation[15]

18 specimens are tentatively assigned to Acipenser sp.[16]

Acipenser sp. is tentatively referred to the genus.[13]

Amia[22]

A. fragosa[22]

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

Amia calva 1908

Belonostomus[13][22]

B. longirostris[13][22]

Lower to upper Hell Creek Formation[15]

28 specimens[16]

A long-snouted slender fish classified as an aspidorhynchid.[13]

Coriops[24]

C. amnicolus[24]

Kindleia[13]

K. fragosa[13]

Lower to uppermost Hell Creek Formation[15]

2610 specimens have been assigned to Kindleia, making it an extremely common genus.[16]

Kindleia is a genus assigned to Amiidae, along with Melvius and Amia.[13]

Lepisosteus[13][22]

L. occidentalis[13][22]

Lower to uppermost Hell Creek Formation[15]

938 specimens are assigned to Lepidosteus[16]

A lepidosteid that is very common in the Hell Creek Formation.[13]

Lepisosteus oculatus1

Melvius[13]

M. thomasi[13]

Lower to upper Hell Creek Formation[15]

6 specimens are assigned to Melvius[16]

A large amiid fish.[13]

Phyllodus

P. paulkatoi

fish with columnar teeth

Palaeolabrus[22]

P. montanensis[22]

Paleopsephurus[22]

P. wilsoni[22]

A paddlefish

Palaeolabrus

P. montanensis

fish (incertae sedis)

Paralbula[26]

P. casei[26]

Platacodon[24]

P. nanus[24]

small teleost fish

Protamia[22]

Indeterminate[22]

Pachyrhizodontoidei

Indeterminate

Fish

Protoscaphirhynchus[22]

P. squamosus[22]

a sturgeon

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

Chiloscyllium[27]

C. sp.[27]

A member of Hemiscylliidae.[27]

Chiloscyllium griseum Oceanopolis

Galagadon[28]

G. nordquistae

  • South Dakota

Isolated teeth

A carpet shark

Lonchidion[29]

L. selachos[29]

Lower to upper Hell Creek Formation[15]

40 specimens[16]

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.[13]

Myledaphus[27]

M. pustulosus[27]

Lower to upper Hell Creek Formation.[15]

1677 specimens[16] previously assigned to M. bipartitus.[27]

Is an anacoracid batoid[13] rajiform related to guitarfishes.[27] Described on the basis of teeth formerly assigned to the species M. bipartitus.[27] The material assigned to Myledaphus bipartitus and makes up 16.5% of the vertebrate remains.[13]

Protoginglymostoma[27]

P. estesi[27]

A member of Ginglymostomatidae.[27] Formerly assigned to the genus Brachaelurus.

Restesia[27]

R. americana[27]

Middle Hell Creek Formation[15]

5 specimens previously assigned to Squatirhina[16]

A wobbegong-like shark.[27] Formerly assigned to Squatirhina. The remains consist of 0.05% of the vertebrates.[16] Also known from the Lance Formation.[27]

Carcharhinidae indet.[28]

Indeterminate

  • South Dakota

An isolated tooth.

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

Ankylosaurus[32]

A. magniventris[32]

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

Ankylosaurus magniventris reconstruction

Denversaurus[32]

D. schlessmani[32]

A nodosaurid ankylosaur.

Dinosaur exhibit - Houston Museum of Natural Science - DSC01881

Edmontonia

E. sp.[34]

  • Montana

isolated teeth

A nodosaurid ankylosaur

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

Dracorex[36]

D. hogwartsia[36]

A pachycephalosaur, possibly synonymous with Pachycephalosaurus.

Dracorex BW

Pachycephalosaurus[32]

P. wyomingensis[32]

A pachycephalosaur. Also found in the Lance Formation.

Pachycephalosaurus Reconstruction

Sphaerotholus[32]

S. buchholtzae[32]

"Skull material."[37]

Sphaerotholus

Stygimoloch[32]

S. spinifer[32]

  • Montana[32]
  • South Dakota
  • North Dakota

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

Stygimoloch NT small

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

Leptoceratops[32]

Leptoceratops c.f. gracilis[32]

A small primitive-looking ceratopsian.

Leptoceratops BW

Tatankaceratops

T. sacrisonorum

  • South Dakota

A ceratopsian possibly synonymous with Triceratops[41]

Tatankaceratops NT

Torosaurus[13][32]

T. latus[13][32]

Upper Hell Creek Formation[15]

A ceratopsian possibly synonymous with Triceratops.[42] A rare ceratopsid.[15]

Torosaurus life restoration

Triceratops[13][32]

T. horridus[13][32]

Lowermost to the middle Hell Creek Formation[44]

4 specimens are assigned to Triceratops horridus from the Hell Creek Formation.[16] Very common

A ceratopsian.[13] Also found in the Evanston, Frenchman, Lance, Laramie, and Scollard Formations.

Triceratops Specimen at the Houston Museum of Natural Science v01

T. prorsus[32]

  • Montana[32]
  • South Dakota
Upper 1/3 of the Hell Creek Formation[44]

Very common.

Also found in the Frenchman and Lance Formations.

Triceratops mount

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

Edmontosaurus

E. annectens

  • Anatosaurus annectens[45]
  • Anatotitan copei[45]
  • Montana[32]
  • South Dakota[33]
  • North Dakota(Mummy Fossil)

Very common.

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

Anatotitan BW

Thescelosaurus[33]

T. garbanii[46]

  • Bugenasaura garbanii

T. neglectus[13][33]

Lower to upper Hell Creek Formation[15]

50 specimens[16]

A small thescelosaurine. Also found in the Frenchman, Lance, Laramie, and Scollard Formations.[48]

Thescelosaurus filamented

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

Tyrannosaurus[13][32]

T. rex[13][32]

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.

Tyrannosaurus-rex-Profile-steveoc86

Nanotyrannus?[13][32]

N.lancensis[13][32]

  • Stygivenator?
  • Deinodon lancensis
  • Albertosaurus lancensis[32]
  • Tyrannosaurus lancensis?
  • Montana
  • Wyoming

A few specimens are known

Lower to upper Hell Creek Formation.

Genus is possibly invalid, its possibly a juvenile T. rex.

Nanotyrannus NT

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

"Orcomimus"

unnamed

One partial skeleton.

An ornithomimid. Numem nudum

Struthiomimus[33]

S. sedens[53]

  • 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.[53]

Struthiomimus BW

Ornithomimus

O. velox[53]

  • Montana
  • South Dakota
  • North Dakota

Fragmentary specimens

A ornithomimid which was also found in the Denver Formation.

"Ornithomimus" sp. by Tom Parker

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

Anzu[32][55]

A. wyliei[55]

Lower to upper Hell Creek Formation[16]

12 well-preserved specimens[15]

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.[55]

Anzu wyliei

Leptorhynchos

L. elegans

  • Montana

An extinct genus of caenagnathid.

Leptorhynchos elegans

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

Acheroraptor[56]

A. temertyorum [56]

Lower? to upper Hell Creek Formation[13]

  • ROM 63777, a maxilla and tooth[56]
  • ROM 63778, a partial dentary[56]
  • isolated teeth[56]

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.[56]

Acheroraptor reconstruction

Avisaurus[13]

A. archibaldi[13][32]

Middle Hell Creek Formation[15]

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

An avisaurid.[13]

Avisaurus and Brachychampsa by tomozsaurus

cf. A. archibaldi[57]

Uppermost Hell Creek Formation[57]

  • YPM 57235, a coracoid

An avisaurid tentatively referred to A. archibaldi based on its size.[57]

A. sp.[58]

  • distal tarsals, metatarsus (juvenile)[58]

Brodavis[59]

B. baileyi[59]

  • UNSM 50665, a left tarsometatarsus missing proximal end, trochleae II and III.[59]

A primitive hesperornithiform.[59]

Dakotaraptor[60]

D. steini [60]

Upper Hell Creek Formation[60]

  • PBMNH.P.10.113.T, a partial skeleton.[60]
  • PBMNH.P.10.115.T, a tibia.[60]
  • PBMNH.P.10.118.T, an astragalocalcaneum.[60]
  • isolated teeth.[60]

A dromaeosaurid. Second-largest dromaeosaurid known.[56]

Dakotaraptor wiki

Potamornis[59]

P. skutchi [61]

  • UCMP 117605, a tarsometatarsus

A hesperornithiform also found in the Lance Formation.[61]

"Unnamed enantiornithine B"[57]

Unnamed

  • YPM 57823, a partial coracoid[57]

An unnamed enantiornithean.[57]

"Unnamed hesperornithiform A"[57]

Unnamed

  • Montana
  • UCMP 13355, a tarsometatarsus

A primitive hesperornithiform.[59] The Hell Creek specimen was referred to the same unnamed taxon as RSM P 2315.1 from the Canadian Frenchman Formation.[57] RSM P 2315.1 was later made the holotype of Brodavis americanus.[59] May be a synonym of Potamornis.[57]

"Unnamed ornithurine B"[57]

Unnamed[62]

  • UCMP 129143, a partial coracoid[57]

An ornithurine possibly similar to Cimolopteryx[57][62]

"Unnamed ornithurine C"[57]

Unnamed

  • SDSM 64281A, a partial coracoid[57]
  • SDSM 64281B, a partial coracoid[57]
  • UCMP 175251, a partial coracoid[57]
  • MOR 2918, a partial coracoid[57]

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[57]

"Unnamed ornithurine D"[57]

Unnamed

  • UCMP 187207, a partial coracoid[57]

An ichthyornithean also present in the Frenchman Formation[57]

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

Azhdarchidae spp.

Indeterminate

  • Montana[64]
  • 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.[64]

Pterosaur spp.[65]

Indeterminate

  • South Dakota
Crocodylomorphs reported from the Hell Creek Formation
Genus Species State Stratigraphic position Material Notes Images

Borealosuchus[66]

  • Montana
  • North Dakota
  • South Dakota

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

Borealosuchus species Borealosuchus wilsoni 1

Brachychampsa[66]

  • Montana
  • South Dakota
  • North Dakota

Extinct genus of alligatoroid.

Brachychampsa sp. - Natural History Museum of Utah - DSC07244 Brachychampsa NT small

Thoracosaurus[66]

  • T. neocesariensis[66]
  • Montana

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

Thoracosaurus macrorhynchus - Maastricht Thoracosaurus

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

Adocus[67]

Indeterminate[67]

Extinct genus of aquatic turtles belonging to the family Adocidae.

Adocidae - Adocus punctatus

Axestemys[69]

A. splendida

  • North Dakota
  • South Dakota

Trionychidae turtle.

Compsemys[67]

C. victa[67]

A relative of Dermatemydidae.

Peckemys

P. brinkman

  • Montana
  • North Dakota

A relative of Baenidae.

Emarginachelys

E. cretacea

  • Montana

A relative of chelydrids.[70]

Eubaena[67]

E. cephalica[67]

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[70]

H. clark[70]

A kinosternoid related to the Central American river turtle.[70]

Plastomenus

P. sp

Trionychidae turtle.

Basilemys

B. sinuosa

Largest dermatemydid land tortoise.

Trionyx[67]

Indeterminate[67]

A genus of softshell turtles belonging to the family Trionychidae.

Trionychidae - Trionyx messelianus

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.

Baena arenosa AMNH 1112

Thescelus

T. insiliens

Baenid turtle.

Chelydridae

Indeterminate

Chelydrids-like turtle.

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

Cemeterius[71][72]

C. monstrosus[71][72]

A platynotan lizard of uncertain phylogenetic placement, also known from the Lance Formation.[71]

Cerberophis[71][72]

C. robustus[71][72]

An alethinophidian snake of uncertain phylogenetic placement.[71]

Obamadon[71][72]

O. gracilis[71][72]

A polyglyphanodontian lizard of uncertain phylogenetic placement. Also known from the Lance Formation.[71]

Peneteius[71]

P. aquilonius[71]

A chamopsiid polyglyphanodontian lizard.[71]

Haptosphenus

H. placodon

Teiidae lizard.

Goldteju Tupinambis teguixin

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.

Chin-krokodilschwanzechse-01

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.

Boa constrictor (2)

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

Champsosaurus[66]

C. sp.[66]

  • Montana

champsosaur.

Champsosaurus BW
Large williston champsosaurus

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

Cimexomys[73]

C. minor[73]

A multituberculate of uncertain phylogenetic placement.

Cimexomys minor

Cimolodon[73]

C. nitidus

  • Montana
  • North Dakota[73]

A cimolodontid multituberculate.

C. cf. nitidus[73]

A cimolodontid multituberculate.

C. sp.[73]

A cimolodontid multituberculate.

Cimolomys[73]

C. gracilis

A cimolodontid multituberculate.

Ptilodus

A cimolomyid multituberculate.

Essonodon[73]

E. browni[73]

A cimolomyid multituberculate.

Meniscoessus[73]

M. conquistus

A cimolomyid multituberculate.

Meniscoessus skull

M. robustus

  • Montana
  • North Dakota
  • South Dakota[73]

A cimolomyid multituberculate.

Meniscoessus robustus

M. cf. robustus

A cimolomyid multituberculate.

M. sp.

A cimolomyid multituberculate.

?M. sp.[73]

A cimolomyid multituberculate.

Mesodma[73]

M. formosa

  • Montana
  • South Dakota[73]

A neoplagiaulacid multituberculate.

M. cf. formosa

A neoplagiaulacid multituberculate.

M. hensleighi

  • Montana
  • South Dakota[73]

A neoplagiaulacid multituberculate.

M. cf. hensleighi

A neoplagiaulacid multituberculate.

M. thompsoni

  • Montana
  • North Dakota
  • South Dakota[73]

A neoplagiaulacid multituberculate.

M. cf. thompsoni

A neoplagiaulacid multituberculate.

M sp.[73]

A neoplagiaulacid multituberculate.

?M sp.[73]

A neoplagiaulacid multituberculate.

?Neoplagiaulax[73]

?N. burgessi[73]

A neoplagiaulacid multituberculate.

Paracimexomys[73]

P. priscus[73]

A multituberculate of uncertain phylogenetic placement.

Paressonodon[74]

P. nelsoni[74]

A cimolomyid multituberculate.

Stygimys

S. kuszmauli

  • Montana

It was a member of the extinct order Multituberculata.

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

Aletridelphys[75][76]

A. florencae

  • Montana
  • North Dakota
  • South Dakota[73]

A pediomyid.

A. hatcheri[75]

  • Montana
  • South Dakota[73]

A pediomyid.

Alphadon[73]

A. marshi

  • Montana
  • North Dakota[73]

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[73]

An alphadontid.

A. wilsoni

An alphadontid.

A. cf. wilsoni

An alphadontid.

A. sp.[73]

  • North Dakota
  • South Dakota[73]

An alphadontid.

Alphadon sp. - MUSE

Didelphodon[73]

D. padanicus

A stagodontid.

D. vorax

  • Montana
  • North Dakota[73]

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

The Childrens Museum of Indianapolis - Didelphodon mandible
Didelphodon Clean

D. cf. vorax

A stagodontid.

Didelphodon Skull Clean

D. sp.

A stagodontid.

cf. D. sp.[73]

  • North Dakota
  • South Dakota[73]

A stagodontid.

Glasbius[73]

G. twitchelli

A glasbiid.

G. cf. twitchelli[73]

A glasbiid.

Leptalestes[75]

L. cooki

A pediomyid.

L. krejcii[75]

  • Montana
  • South Dakota[73]

A pediomyid.

Nanocuris[74]

N. improvida[74]

A deltatheridiid.

Nortedelphys

N. jasoni (= N. intermedius)[74][77]

  • Montana
  • South Dakota

A herpetotheriid.

Pediomys[73]

P. elegans[73]

  • Montana
  • South Dakota[73]

A pediomyid.

Protalphadon[73]

P. foxi

An alphadontid.

P. lulli[73]

An alphadontid.

Turgidodon[73]

T. rhaister[73]

An alphadontid.

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

Altacreodus

A. magnus

  • Montana
  • North Dakota

a possibe creodont, formally a species of Cimolestes[78]

Alostera[73]

A. saskatchewanensis[73]

A eutherian of uncertain phylogenetic placement.

Ambilestes

A. cerberoides

  • Montana

A eutherian of uncertain classification, formally a species of Cimolestes

Batodon[73]

B. tenuis[73]

A cimolestid eutherian.

Cimolestes[73]

C. incisus

A cimolestid eutherian.

C. stirtoni[73]

A cimolestid eutherian.

Gypsonictops[73]

G. hypoconus

  • Montana
  • South Dakota[73]

A gypsonictopsid eutherian.

G. illuminatus

  • Montana
  • North Dakota[73]

A gypsonictopsid eutherian.

G. cf. illuminatus

A gypsonictopsid eutherian.

G. sp.[73]

A gypsonictopsid eutherian.

cf. Paranyctoides[73]

cf. Paranyctoides sp.[73]

A nyctitheriid eutherian.

Protungulatum[75]

P. coombsi[75]

A stem-placental.

Protungulatum donnae

Purgatorius

P. ceratops

  • Montana

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

Purgatorius BW

Scollardius

S. propalaeoryctes

  • Montana

A eutherian of uncertain classification, formally a species of Cimolestes

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

Aquilapollenites Attenuatus Funkhouser(1961)

Alnipollenites

"Ficus"

"Ficus" planicostata

Sycomoros old

"Ficus" artocarpoides

"Ficus" trinervis

Ilexpollenites

Ilexpollenites compactus

Interpollis

Interpollis cf. I. supplingensis

Balmeisporites

Balmeisporites sp.

Marmarthia

Marmarthia pearsonii

"Myrica"

"Myrica" torreyi

Myrica faya

Platanites

Platanites marginata

Sabalites

Sabalites sp.

Tricolpites

Tricolpites interangulus

Metasequoia

M. sp

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

MetaseqLeaves

"Grewiopsis"

"G" saportana

Another generic Hamamelididae.

Annona?

A?. robusta

Abundant at Brownie Butte, Montana.

Annona muricata Blanco1.196

Cobbania

C. corrugata

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

Pistia stratiotes0

Araucaria

A. araucana

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

Araucaria araucana cones

Artocarpus

A. lessigiana

Abundant at Brownie Butte, Montana.

Starr 031209-0044 Artocarpus altilis

Celastrus

C. taurenensis

Some may be Eucommiacaea.

Celastrus scandens

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.

CinnamonLeaves

Cissu

C. marginata

Also spelled "marginatus".

Juglans

J. leconteana

Juglans major Morton

Liriodendrites

L. bradacci

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

Liriodendron

L. laramiense

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

Liriodendron tulipifera

Leepiesceia

L. presrtocarpoides

another laurel.

Marmarthia

M. pearsonii

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

Lauraceae sp Blanco2.360

M. trivialis

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

Platanites

P. marginata

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

London plane flower

Quercus

Q. viburnifolia

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

Dombeyopsis

D. trivialis

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

D. obtusa

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

Rhamnus

R. cleburnii

A buckthorn look-alike.

Rhamnus frangula - Köhler–s Medizinal-Pflanzen-120

Vitis

V. stantonii

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

Abhar-iran

Ziziphus

Z. fibrillosus

Zizyphus zizyphus Ypey54

Androvettia

A. catenulata

Araliaephyllum

A. polevoi

Bisonia

B. niemii

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

Cannabaceae

C. sp

Cannabis 01 bgiu

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

Ginkgo adiantoides - G. cranii

Glyptostrobus

G. nordenskioldii

Glyptostrobus 01

G. sp

Glyptostrobus pensilis 2007.06.28 10.10.35-p6280031

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.

M.macrophylla var. ashei 200706

Marchantia

M. pealii

MarchantiaPolymorpha

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

Rhamnus frangula

Sabalites

S. sp

Palm tree.

Puka beach

Sapindopsis

S. powelliana

Sequoites

S. artus

Sequoia tree.

Del Norte Titan 230

Taxodium

T. olrikii

Related to today's bald cypress.

Taxodium distichum NRCSMS01010

Trochodendroides

T. arctica

T. nebrascensis

Zingiberopsis

Z. attenuata

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

Zingiber officinale Blanco1.131

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

Populus tremula 002

Cocculus

cf. C. flabella

Cocculus orbiculatus HRM

Cissites

cf. C. acerifolia

Pistia

cf. P. corrugata

Floating aquatic herb.

Pistia stratiotes 2

Palaeoaster

P. inquirenda

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

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