Acheroraptor

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Acheroraptor
Temporal range: Late Cretaceous (Maastrichtian), 67.2–66  Ma
Acheroraptor NMNH.jpg
Casts of the holotype maxilla and referred dentary, National Museum of Natural History.
Scientific classification OOjs UI icon edit-ltr.svg
Kingdom: Animalia
Phylum: Chordata
Class: Reptilia
Clade: Dinosauria
Clade: Saurischia
Clade: Theropoda
Clade: Pennaraptora
Clade: Paraves
Family:† Dromaeosauridae
Genus:† Acheroraptor
Evans et al., 2013
Type species
†Acheroraptor temertyorum
Evans et al., 2013

Acheroraptor ("underworld thief") is an extinct genus of dromaeosaurid theropod dinosaur that lived in present-day Montana in the United States during the Maastrichtian stage of the Late Cretaceous period. It was described by Canadian paleontologists David Evans, Derek Larson, and Philip J. Currie in 2013. The genus contains a single species, A. temertyorum, named on an isolated maxilla with teeth. An incomplete dentary found nearby was also assigned to the species. These fossils were initially discovered by fossil poachers, though they were later sold to the Royal Ontario Museum, in layers belonging to the Hell Creek Formation. This indicates that these fossils date to the upper Maastrichtian stage, 67.2-66 million years ago. Acheroraptor is one of several dinosaurs known from the Hell Creek Formation, however it is the only named definitive dromaeosaurid.

Contents

Many gigantic dinosaurs are known from the Hell Creek Formation, including the tyrannosaurid theropod Tyrannosaurus , ceratopsids Torosaurus and Triceratops , ankylosaurians Ankylosaurus and Denversaurus , and hadrosaurid Edmontosaurus . Medium-sized herbivorous and omnivorous dinosaurs, such as the thescelosaurid Thescelosaurus , pachycephalosaurids Pachycephalosaurus and Sphaerotholus , and oviraptorosaur Anzu , are known, however few medium-sized carnivorous dinosaurs were known before Acheroraptor. Beyond the jaw material, Acheroraptor is possibly known from isolated teeth formerly assigned to Saurornitholestes and Dromaeosaurus . The formation had a warm, humid, and swampy environment, reflecting maritime to subtropical conditions. Western North America at the time was blanketed in ferns, conifers, angiosperms, ginkgoes, and cycads. Fish like gars, sturgeons, and paddlefish, chondrichthians like hybodonts and sharks, and crocodylomorphs like Borealosuchus and Thoracosaurus swam in the waterways, while lizards, amphibians, and mammals lived in the undergrowth.

Discovery and naming

Fossils of Acheroraptor were first collected on 28 August, 2009 by a group of fossil poachers in sediments of the Hell Creek Formation in a site 45 kilometres (28 mi) southwest of Jordan, Garfield County, Montana in the western United States. The remains found consisted of a complete right maxilla with several maxillary teeth, cataloged as ROM 63777 at the Royal Ontario Museum in Toronto, and an assigned dentary, ROM 63778. The two fossils were found in a layer of reddish sandstone made up of a bonebed including other small vertebrate and invertebrate shell fossils, though the dentary was found around 4 metres (13 ft) away in the same layer. Photographs of the fossils in situ and GPS data was provided the fossil poachers, one of whom collected the dentary several years after the maxilla was found. The ROM subsequently purchased the two fossils from a private collector. The strata where these fossils were unearthed derives from the upper part of the Hell Creek Formation, dating to the latest Maastrichtian stage of the Late Cretaceous, immediately prior to the Cretaceous–Paleogene extinction event. [1]

Size of Acheroraptor compared to a human AcheroraptorSize.svg
Size of Acheroraptor compared to a human

In 2013, Canadian paleontologists David Evans, Derek Larson, and Philip J. Currie scientifically described the remains and assigned them to a new genus and species of dromaeosaurid theropod, which they named Acheroraptor temertyorum. The generic name Acheroraptor is a combination of the Greek word Ἀχέρων, Acheron, "underworld", in reference to the provenance from the Hell Creek Formation, and the Latin word raptor, "thief", a common suffix in dromaeosaurid names. The specific name honors James and Louise Temerty, the chairman of Northland Power and the ROM Board of Governors and his wife, who have supported the museum for many years. The maxilla ROM 63777 was selected as the holotype specimen of A. temertyorum. [1]

The discovery of Acheroraptor was significant as it was the first diagnostic late Maastrichtian North American dromaeosaurid reported in literature, though the possibly chimeric Dakotaraptor [2] and the New Mexican Dineobellator are now known as well. [3] An abstract from the 2020 Canadian Society of Vertebrate Paleontology Meeting reported new findings on Acheroraptor and its holotype locality (abbreviated as AHL). Instead of belonging to the upper half of the Hell Creek Formation, the AHL actually comes from the lower-middle half based on palynological data. [4] Additionally, postcranial material consisting of three manual phalanges and a claw were assigned to Acheroraptor. [5]

Description

In its initial description, Acheroraptor was described as a "mid-sized" dromaeosaurid. The lead author of its description stated that it was similar in size to Deinonychus , [6] which was estimated to be around 3.3–3.4 meters (10 ft 10 in – 11 ft 2 in) long and 60–73 kg (132–161 lb) [7] [8] or even 100–73 kg (220–161 lb) in mass. [9]

A speculative life restoration Acheroraptor reconstruction.jpg
A speculative life restoration

The holotype includes a nearly complete right maxilla and several teeth, with minor crushing, cracks, and missing a small section of the jugal ramus . The anterior region of the antorbital fossa , which Evans, Larson and Currie (2013) defined as the zone between the anterior frontier of the antorbital fenestra and the antorbital fossa, is relatively small when compared to related genera. This zone measures only 20 millimetres (0.79 in) long and is around half the length of the lateral maxillary lamina , forming a ratio of 2.25. In contrast, other North American dromaeosaurids like Bambiraptor and Saurornitholestes have a much larger anterior region and lower ratio. In this area are the promaxillary and maxillary fenestrae as well, which are overall similar to those of dromaeosaurids like Atrociraptor and Saurornitholestes. The height between the maxillary fenestra and the tooth row is less than twice that of the height of the largest maxillary tooth in Acheroraptor and taxa such as Saurornitholestes, Deinonychus, Dromaeosaurus, and Bambiraptor. [1]

As for the referred dentary, its preserved section bears 15 alveoli, though it likely had 16 or 17 teeth per dentary. The presence of a vertically oriented Meckelian groove and fused interdental plates suggest that the dentary does not belong to Richardoestesia or a troodontid, which are also known from the Hell Creek Formation. At the apex of the dentary is a slight "chin", one much weaker than that observed in the related Velociraptor . [1]

Classification

Acheroraptor belonged to the family Dromaeosauridae, a group of theropods that existed during the Cretaceous in the Americas, Antarctica, Asia, and Oceania. This group includes several subfamilies as well in addition to Eudromaeosauria ("the true dromaeosaurids"), [10] which contains Acheroraptor. [11] [1] Outside of the node Eudromaeosauria is three subfamilies: Microraptorinae, Halszkaraptorinae, and Unenlagiinae. [12] Within Eudromaeosauria includes the subfamilies Dromaeosaurinae, Saurornitholestinae, and Velociraptorinae, however the classification of genera within these groups and their relationships to each other are unclear.

The position of Acheroraptor within Dromaeosauridae has been contentious; Evans, Larson, and Currie (2013) phylogenetic analyses used several data matrices. Both specimens of Acheroraptor were coded as a single taxon into Turner et al. (2012) data matrix, an extensive phylogenetic analysis of theropods that focuses on maniraptorans. Acheroraptor was recovered as a member of the clade containing Eudromaeosauria and Microraptorinae, confirming its referral to the Dromaeosauridae, and possibly to Eudromaeosauria. Within that clade, however, most taxa were recovered in a large polytomy, due to the limited codings available for Acheroraptor. [1]

Evans et al. (2013) also coded the specimens of Acheroraptor (together and separately) into an updated version of the smaller, dromaeosaur-specific dataset from Longrich and Currie (2009). Velociraptor osmolskae and Balaur bondoc were added, Itemirus was excluded (following its identification as a tyrannosauroid by Miyashita and Currie (2009)), and following Turner et al. (2012) the codings for Adasaurus mongoliensis were separated into these based on the holotype from the Nemegt Formation, and these based on IGM 100/23 from the Bayanshiree Formation. Several characters were also rescored and modified, and two maxillary characters were added to the matrix from Turner et al. (2012). This analysis yielded a more resolved topology, placing Acheroraptor in a relatively basal position within the Velociraptorinae, which was otherwise found to include only Asian dromaeosaurids. The cladogram below shows the phylogenetic position of Acheroraptor following this analysis. [1]

Dromaeosauridae

In studies since, Acheroraptor has been recovered in various positions in Dromaeosauridae. In two 2020 studies, Acheroraptor was classified as a basal member of the subfamily Velociraptorinae which, along with taxa like Dineobellator or even Deinonychus, would extend the known range of the group to North America. [13] [3] However, the 2015 description of Boreonykus recovered Acheroraptor in a polytomy in Velociraptorinae with little recognition of its affinities. [14] In contrast, a 2020 paper describing Hesperornithoides found Acheroraptor as a member of Microraptorinae, a clade of arboreal, gliding dromaeosaurids previously restricted to the Early Cretaceous period. However, the authors said it had little support and that the use of isolated jaws for classification was unreliable. [15] A 2022 study of eudromaeosauria reclassified Acheroraptor as a derived member of Saurornitholestinae, with Atrociraptor as its sister taxon, [11] a result replicated by other papers. [16] [17] The results of Jasinski and colleagues (2022) are below: [16]

Reconstruction of the skull of Acheroraptor as a saurornitholestine, known material highlighted in white. Acheroraptor skull reconstruction.png
Reconstruction of the skull of Acheroraptor as a saurornitholestine, known material highlighted in white.
Dromaeosauridae

Paleobiology

An examination of the bite force of Acheroraptor suggests that like members of the Velociraptorinae, it was equipped with relatively weak jaws for inflicting rapid, slashing bites on smaller prey. This likewise indicates that saurornitholestines were more diverse in predation habits and ecological roles than previously assumed. [18]

Paleoecology

Acheroraptor and other fauna from Hell Creek (Acheroraptor in light orange) Hell Creek Formation Fauna.png
Acheroraptor and other fauna from Hell Creek (Acheroraptor in light orange)

Acheroraptor was found in the Hell Creek Formation, which spans parts of modern-day Montana, South Dakota, North Dakota, and Wyoming. The depositional environment of this region was warm, humid, and swampy environment, reflecting maritime to subtropical conditions. [19] [20] The average temperatures ranged from 11.3–11.6 °C (52.3–52.9 °F). [20] The landscape featured lush, low-lying vegetation dominated by ferns, while the forest canopy consisted of a mixture of diverse conifers (redwoods, cypresses, and pine-like trees) and angiosperms (flowering plants including sycamores, members of the magnolia family, rosids, laurels, various palms, and more). Cycads and Ginkgo trees were also present. [21] The wetlands and waterways contained a diverse faunal assemblage. Small insects are known from what would have been the swampy forests, [22] while the rivers and lagoons hosted invertebrates (bivalves and ammonites), fish (sharks, hybodonts, gars, and sturgeons), amphibians (frogs and salamanders), and various reptiles (turtles, crocodilians, the choristodere Champsosaurus , and mosasaurs in the coastal, brackish, and freshwater zones). Small terrestrial mammals and lizards were diverse, living alongside early snakes. [23] [24] Pterosaurs are represented by the azhdarchid Infernodrakon [25] and an unnamed pteranodontian. [26]

The holotype locality of Acheroraptor comes from a non-marine site preserving a diverse array of macro and microvertebrate taxa, giving an insight into the paleobiology of the Hell Creek Formation. [5] Macrofossil taxa are represented by the dinosaurs Sphaerotholus buchholtzae and Pachycephalosaurus (pachycephalosaurid ornithischians), Anzu (a caenagnathid theropod), and Acheroraptor itself, and the crocodylian Borealosuchus . Isolated teeth from hadrosaurids, ceratopsids, tyrannosaurids, oviraptorosaurs, dromaeosaurids, and troodontids were found too, though their identities are indeterminate beyond the family level. As for microfossil taxa, a variety of freshwater fish including the guitarfish Myledaphus and indeterminate sturgeons, gars, holosteans and amiids are represented. Additionally, amphibians such as the salamander Scapherpeton and an indeterminate frog as well as the turtle Basilemys and indeterminate baenid, chelydrid, and adocid turtles are known. [5]

Acheroraptor is one of the geologically youngest dromaeosaurids known, along with taxa like Dineobellator and Dakotaraptor. [1] Evans, Larson, and Currie (2013) concluded that Acheroraptor was the only dromaeosaurid from the Hell Creek Formation, and that teeth previously referred to Dromaeosaurus and Saurornitholestes actually came from the taxon. Furthermore, the authors concluded that there was probably only one dromaeosaurid in the Hell Creek-Lance assemblage. [1] In 2015, this view was disproven, with the description of Dakotaraptor, a far larger second dromaeosaur from the formation. [2] However, the validity of this taxon is uncertain; its material is likely chimeric, including bones from turtles, oviraptorosaurs, and ornithomimids. [27] [28] [3]

The Hell Creek Formation is divided into two layers; upper and lower. Although initially thought to come from the former, [1] a 2020 abstract suggests Acheroraptor came from the latter. [5] The fauna and flora of these layers differ, with some species such as Triceratops horridus only coming from the lower layer whereas T. prorsus derives from the upper layer. Non-dromaeosaurid theropods known from the formation include the tyrannosauroids Tyrannosaurus and Nanotyrannus , [25] the alvarezsaurid Trierarchuncus , [29] the oviraptorosaurs Anzu, Leptorhynchos, Eoneophron, [30] and a large, undescribed Gigantoraptor -like ichnotaxon, [31] the ornithomimids Struthiomimus, "Orcomimus", and Ornithomimus , [32] the troodontids Paronychodon, Troodon, Pectinodon, and Richardoestesia, [33] and birds like Avisaurus, Magnusavis, [34] and Potamornis . [35]

In addition to theropod dinosaurs, ornithischians are represented by members of Ankylosauria, Ceratopsia, Pachycephalosauridae, and Ornithopoda. Fossils of the large, armored ankylosaurians Ankylosaurus [36] and Denversaurus in addition to those of horned ceratopsians like Leptoceratops, Triceratops, Torosaurus , and the potentially valid Tatankaceratops [37] [38] and Nedoceratops . [39] [40] Fossils of the thescelosaurid Thescelosaurus and hadrosaurid Edmontosaurus, members of Ornithopoda, are also known. [41] [42] The unique, "bone-headed" pachycephalosaurids are known by a menagerie of genera, such as Pachycephalosaurus, Platytholus, Sphaerotholus, and the possibly valid Stygimoloch . [43] [32] [44]

See also

References

  1. 1 2 3 4 5 6 7 8 9 10 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. S2CID   14978813.
  2. 1 2 DePalma, R.A.; Burnham, D.A.; Martin, L.D.; Larson, P.L.; Bakker, R.T. (2015). "The First Giant Raptor (Theropoda: Dromaeosauridae) from the Hell Creek Formation". Paleontological Contributions (14): 1–16. doi: 10.17161/paleo.1808.18764 . hdl: 1808/18764 . S2CID   17099603.
  3. 1 2 3 Jasinski, Steven E.; Sullivan, Robert M.; Dodson, Peter (2020-03-26). "New Dromaeosaurid Dinosaur (Theropoda, Dromaeosauridae) from New Mexico and Biodiversity of Dromaeosaurids at the end of the Cretaceous". Scientific Reports. 10 (1): 5105. Bibcode:2020NatSR..10.5105J. doi:10.1038/s41598-020-61480-7. ISSN   2045-2322. PMC   7099077 . PMID   32218481.
  4. ↑ Woodruff, D. Cary; Schott, Ryan K.; Evans, David C. (November 2023). "Two new species of small‐bodied pachycephalosaurine (Dinosauria, Marginocephalia) from the uppermost Cretaceous of North America suggest hidden diversity in well‐sampled formations". Papers in Palaeontology. 9 (6). doi:10.1002/spp2.1535. ISSN   2056-2799.
  5. 1 2 3 4 Wilkinson, Ryan D.; Cullen, Thomas M.; Evans, David C. (2020). "The diverse faunal assemblage of the Acheroraptor temertyorum holotype locality from the Hell Creek Formation of Montana, USA". 8th Annual Meeting Canadian Society of Vertebrate Palaeontology. 8: 60.
  6. ↑ Evans, David (2013-12-16). "New Hell Creek Dromaeosaurid Described". David Evans Lab. Retrieved 2026-04-07.
  7. ↑ Paul, G. S. (2016). The Princeton Field Guide to Dinosaurs (2nd ed.). Princeton, New Jersey: Princeton University Press. p. 153. ISBN   978-0-691-16766-4.
  8. ↑ Paul, Gregory Scott (1988). Predatory Dinosaurs of the World. New York: Simon and Schuster. pp.  358, 366–369. ISBN   978-0-671-61946-6.
  9. ↑ Campione, Nicolas E.; Evans, David C.; Brown, Caleb M.; Carrano, Matthew T. (2014). "Body mass estimation in non-avian bipeds using a theoretical conversion to quadruped stylopodial proportions". Methods in Ecology and Evolution. 5 (9): 913–923. Bibcode:2014MEcEv...5..913C. doi: 10.1111/2041-210X.12226 . S2CID   84317234.
  10. ↑ Longrich, Nicholas R.; Currie, Philip J. (2009-03-31). "A microraptorine (Dinosauria–Dromaeosauridae) from the Late Cretaceous of North America". Proceedings of the National Academy of Sciences. 106 (13): 5002–5007. Bibcode:2009PNAS..106.5002L. doi: 10.1073/pnas.0811664106 . PMC   2664043 . PMID   19289829.
  11. 1 2 Powers, Mark J.; Fabbri, Matteo; Doschak, Michael R.; Bhullar, Bhart-Anjan S.; Evans, David C.; Norell, Mark A.; Currie, Philip J. (2022). "A new hypothesis of eudromaeosaurian evolution: CT scans assist in testing and constructing morphological characters" . Journal of Vertebrate Paleontology. 41 (5) e2010087. Bibcode:2021JVPal..41E0087P. doi:10.1080/02724634.2021.2010087. S2CID   247039404.
  12. ↑ Cau, Andrea; Beyrand, Vincent; Voeten, Dennis F. A. E.; Fernandez, Vincent; Tafforeau, Paul; Stein, Koen; Barsbold, Rinchen; Tsogtbaatar, Khishigjav; Currie, Philip J.; Godefroit, Pascal (December 2017). "Synchrotron scanning reveals amphibious ecomorphology in a new clade of bird-like dinosaurs". Nature. 552 (7685): 395–399. Bibcode:2017Natur.552..395C. doi:10.1038/nature24679. ISSN   1476-4687. PMID   29211712.
  13. ↑ Currie, Philip J.; Evans, David C. (April 2020). "Cranial Anatomy of New Specimens of Saurornitholestes langstoni (Dinosauria, Theropoda, Dromaeosauridae) from the Dinosaur Park Formation (Campanian) of Alberta". The Anatomical Record. 303 (4): 691–715. doi:10.1002/ar.24241. ISSN   1932-8486. PMID   31497925.
  14. ↑ Bell, Phil R.; Currie, Philip J. (2016-01-02). "A high-latitude dromaeosaurid, Boreonykus certekorum, gen. et sp. nov. (Theropoda), from the upper Campanian Wapiti Formation, west-central Alberta". Journal of Vertebrate Paleontology. 36 (1) e1034359. Bibcode:2016JVPal..36E4359B. doi:10.1080/02724634.2015.1034359. ISSN   0272-4634.
  15. ↑ Hartman, Scott; Mortimer, Mickey; Wahl, William R.; Lomax, Dean R.; Lippincott, Jessica; Lovelace, David M. (2019-07-10). "A new paravian dinosaur from the Late Jurassic of North America supports a late acquisition of avian flight". PeerJ. 7 e7247. Bibcode:2019PeerJ...7e7247H. doi: 10.7717/peerj.7247 . ISSN   2167-8359. PMC   6626525 . PMID   31333906.
  16. 1 2 Jasinski, Steven E.; Sullivan, Robert M.; Carter, Aja M.; Johnson, Erynn H.; Dalman, Sebastian G.; Zariwala, Juned; Currie, Philip J. (2022-11-07). "Osteology and reassessment of Dineobellator notohesperus, a southern eudromaeosaur (Theropoda: Dromaeosauridae: Eudromaeosauria) from the latest Cretaceous of New Mexico" . The Anatomical Record. 306 (7): 1712–1756. doi:10.1002/ar.25103. ISSN   1932-8486. PMID   36342817. S2CID   253382718.
  17. ↑ Czepiński, Łukasz (2023). "Skull of a dromaeosaurid Shri devi from the Upper Cretaceous of the Gobi Desert suggests convergence to the North American forms". Acta Palaeontologica Polonica. 68. doi:10.4202/app.01065.2023. ISSN   0567-7920.
  18. ↑ Yun, Chan-Gyu (2024-12-23). "Mandibular biomechanics of Acheroraptor temertyorum (Theropoda: Dromaeosauridae) with implications for the feeding ecology and behaviour" . Mesozoic. 1 (4): 459–468. doi: 10.11646/mesozoic.1.4.3 . ISSN   3021-1867.
  19. ↑ Fowler, Denver (2020-11-05). "The Hell Creek Formation, Montana: A Stratigraphic Review and Revision Based on a Sequence Stratigraphic Approach". Geosciences. 10 (11): 435. Bibcode:2020Geosc..10..435F. doi: 10.3390/geosciences10110435 . ISSN   2076-3263.
  20. 1 2 Arens, Nan Crystal; Allen, Sarah E. (2014), "A florule from the base of the Hell Creek Formation in the type area of eastern Montana: Implications for vegetation and climate" , Through the End of the Cretaceous in the Type Locality of the Hell Creek Formation in Montana and Adjacent Areas, Geological Society of America, doi:10.1130/2014.2503(06), ISBN   978-0-8137-2503-1 , retrieved 2025-11-08{{citation}}: CS1 maint: work parameter with ISBN (link)
  21. ↑ Johnson, Kirk R. (2002), "Megaflora of the Hell Creek and lower Fort Union Formations in the western Dakotas: Vegetational response to climate change, the Cretaceous-Tertiary boundary event, and rapid marine transgression" , 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, doi:10.1130/0-8137-2361-2.329, ISBN   978-0-8137-2361-7 , retrieved 2025-11-01{{citation}}: CS1 maint: work parameter with ISBN (link)
  22. ↑ DePalma, Robert; Cichocki, Frederich; Dierick, Manuel; Feeney, Robert (2010). "Preliminary Notes on the First Recorded Amber Insects from the Hell Creek Formation" (PDF). The Journal of Paleontological Sciences.
  23. ↑ Hartman, Joseph Herbert; Johnson, Kirk R.; Nichols, Douglas J. (2002). The Hell Creek formation and the Cretaceous-Tertiary boundary in the northern Great Plains: an integrated continental record of the end of the Cretaceous. GSA Special papers. Boulder (Colo.): Geological society of America. ISBN   978-0-8137-2361-7.
  24. ↑ Wilson, G.P. (2013). "Mammals across the K/Pg boundary in northeastern Montana, U.S.A.: Dental morphology and body-size patterns reveal extinction selectivity and immigrant-fueled ecospace filling" . Paleobiology. 39 (3): 429–469. Bibcode:2013Pbio...39..429W. doi:10.1666/12041. S2CID   36025237.
  25. 1 2 Zanno, Lindsay E.; Napoli, James G. (2025). "Nanotyrannus and Tyrannosaurus coexisted at the close of the Cretaceous". Nature. 648 (8093): 357–367. Bibcode:2025Natur.648..357Z. doi:10.1038/s41586-025-09801-6. ISSN   1476-4687. PMID   41167514.
  26. ↑ Longrich, Nicholas R.; Martill, David M.; Andres, Brian (2018-03-13). "Late Maastrichtian pterosaurs from North Africa and mass extinction of Pterosauria at the Cretaceous-Paleogene boundary". PLOS Biology. 16 (3) e2001663. doi: 10.1371/journal.pbio.2001663 . ISSN   1545-7885. PMC   5849296 . PMID   29534059.
  27. ↑ 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. 3 e1691: e1957. doi: 10.7717/peerj.1691 . PMC   4756751 . PMID   26893972.
  28. ↑ Cau, A. (2024). "A Unified Framework for Predatory Dinosaur Macroevolution". Bollettino della Società Paleontologica Italiana. 63 (1). doi:10.4435/BSPI.2024.08 (inactive 8 April 2026).{{cite journal}}: CS1 maint: DOI inactive as of April 2026 (link)
  29. ↑ Fowler, Denver W.; Wilson, John P.; Freedman Fowler, Elizabeth A.; Noto, Christopher R.; Anduza, Daniel; Horner, John R. (2020-12-01). "Trierarchuncus prairiensis gen. et sp. nov., the last alvarezsaurid: Hell Creek Formation (uppermost Maastrichtian), Montana". Cretaceous Research. 116 104560. Bibcode:2020CrRes.11604560F. doi:10.1016/j.cretres.2020.104560. ISSN   0195-6671.
  30. ↑ Atkins-Weltman, Kyle L.; Simon, D. Jade; Woodward, Holly N.; Funston, Gregory F.; Snively, Eric (2024-01-24). "A new oviraptorosaur (Dinosauria: Theropoda) from the end-Maastrichtian Hell Creek Formation of North America". PLOS ONE. 19 (1) e0294901. Bibcode:2024PLoSO..1994901A. doi: 10.1371/journal.pone.0294901 . ISSN   1932-6203. PMC   10807829 . PMID   38266012.
  31. ↑ Maltese, A. (17 December 2013). "Giant Oviraptor Tracks from the Hell Creek". RMDRC paleo lab. Blogspot. Retrieved 17 December 2013.
  32. 1 2 Weishampel, D.B.; Dodson, P.; Osmólska, H. (2004). The Dinosauria (2nd ed.). Berkeley, California: University of California Press. pp.  861. ISBN   0-520-24209-2.
  33. ↑ Gates, Terry A.; Zanno, Lindsay E.; Makovicky, Peter J. (2015-03-01). "Theropod teeth from the upper maastrichtian hell creek formation "sue" quarry: New morphotypes and faunal comparisons". Acta Palaeontologica Polonica. 60 (1): 131–139. Bibcode:2015AcPaP..60..131G. doi:10.4202/app.2012.0145. ISSN   0567-7920.
  34. ↑ Clark, Alexander D.; Atterholt, Jessie; Scannella, John B.; Carroll, Nathan; O'Connor, Jingmai K. (2024). "New enantiornithine diversity in the Hell Creek Formation and the functional morphology of the avisaurid tarsometatarsus". PLOS ONE. 19 (10) e0310686. Bibcode:2024PLoSO..1910686C. doi: 10.1371/journal.pone.0310686 . ISSN   1932-6203. PMC   11463745 . PMID   39383133.
  35. ↑ Longrich, N.R.; Tokaryk, T.; Field, D.J. (2011). "Mass extinction of birds at the Cretaceous-Paleogene (K-Pg) boundary". Proceedings of the National Academy of Sciences. 108 (37): 15253–15257. Bibcode:2011PNAS..10815253L. doi: 10.1073/pnas.1110395108 . PMC   3174646 . PMID   21914849.
  36. ↑ Arbour, Victoria M.; Mallon, Jordan C. (2017). "Unusual cranial and postcranial anatomy in the archetypal ankylosaur Ankylosaurus magniventris". FACETS. 2 (2): 764–794. Bibcode:2017Facet...2..764A. doi:10.1139/facets-2017-0063.
  37. ↑ Longrich, Nicholas R. (2011-06-01). "Titanoceratops ouranos, a giant horned dinosaur from the late Campanian of New Mexico". Cretaceous Research. 32 (3): 264–276. Bibcode:2011CrRes..32..264L. doi:10.1016/j.cretres.2010.12.007. ISSN   0195-6671.
  38. ↑ Ott, C.J.; Larson, P.L. (2010). "A New, Small Ceratopsian Dinosaur from the Latest Cretaceous Hell Creek Formation, Northwest South Dakota, United States: A Preliminary Description". In Ryan, M.J.; Chinnery-Allgeier, B.J.; Eberth, D.A. (eds.). New Perspectives on Horned Dinosaurs: The Royal Tyrrell Museum Ceratopsian Symposium. Bloomington: Indiana University Press. p. 656.
  39. ↑ Maiorino, Leonardo; Farke, Andrew A.; Kotsakis, Tassos; Piras, Paolo (2013-11-26). "Is Torosaurus Triceratops? Geometric Morphometric Evidence of Late Maastrichtian Ceratopsid Dinosaurs". PLOS ONE. 8 (11) e81608. Bibcode:2013PLoSO...881608M. doi: 10.1371/journal.pone.0081608 . ISSN   1932-6203. PMC   3841114 . PMID   24303058.
  40. ↑ Farke, Andrew A. (2011-01-20). "Anatomy and Taxonomic Status of the Chasmosaurine Ceratopsid Nedoceratops hatcheri from the Upper Cretaceous Lance Formation of Wyoming, U.S.A". PLOS ONE. 6 (1) e16196. Bibcode:2011PLoSO...616196F. doi: 10.1371/journal.pone.0016196 . ISSN   1932-6203. PMC   3024410 . PMID   21283763.
  41. ↑ Lyson, Tyler R.; Longrich, Nicholas R. (2011-04-22). "Spatial niche partitioning in dinosaurs from the latest cretaceous (Maastrichtian) of North America". Proceedings of the Royal Society B: Biological Sciences. 278 (1709): 1158–1164. Bibcode:2011PBioS.278.1158L. doi:10.1098/rspb.2010.1444. ISSN   0962-8452. PMC   3049066 . PMID   20943689.
  42. ↑ Brown, Caleb Marshall; Boyd, Clint A.; Russell, Anthony P. (2011). "A new basal ornithopod dinosaur (Frenchman Formation, Saskatchewan, Canada), and implications for late Maastrichtian ornithischian diversity in North America: A NEW THESCELOSAUR". Zoological Journal of the Linnean Society. 163 (4): 1157–1198. doi:10.1111/j.1096-3642.2011.00735.x.
  43. ↑ Bakker, R.T.; Sullivan, R.M.; Porter, V.; Larson, P.; 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.; Sullivan, R.M. (eds.). Late Cretaceous vertebrates from the Western Interior. New Mexico Museum of Natural History and Science Bulletin. Vol. 35. pp. 331–345.
  44. ↑ Wroblewski, Anton F.-J. (2025-01-31). "Southernmost record of the pachycephalosaurine Stygimoloch spinifer and palaeobiogeography of latest Cretaceous North American dinosaurs". Lethaia. 57 (4): 1–10. doi:10.18261/let.57.4.7. ISSN   0024-1164.
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