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Atrociraptor

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Atrociraptor
Temporal range: Late Cretaceous (Maastrichtian), 68.5 Ma
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Holotype jaw remains at the Royal Tyrrell Museum
Scientific classification Edit this classification
Domain: Eukaryota
Kingdom: Animalia
Phylum: Chordata
Clade: Dinosauria
Clade: Saurischia
Clade: Theropoda
Family: †Dromaeosauridae
Clade: †Eudromaeosauria
Subfamily: †Saurornitholestinae
Genus: †Atrociraptor
Currie & Varricchio, 2004
Species:
†A. marshalli
Binomial name
†Atrociraptor marshalli
Currie & Varricchio, 2004

Atrociraptor (meaning "savage thief"[1]) is a genus of saurornitholestine dromaeosaurid theropod dinosaur from the Late Cretaceous (Maastrichtian stage) of Alberta, Canada.

Discovery[edit]

Skeletal diagram showing the position of the holotype jaw remains

In 1995, the fossil collector Wayne Marshall discovered a partial skull of a dromaeosaurid dinosaur in the Horseshoe Canyon Formation of Drumheller in Alberta, Canada, about 5 km (3.1 mi) west of the Royal Tyrrell Museum of Palaeontology. Marshall had previously worked in the museum's mounting shop, helping to construct exhibits until the museum opened in 1985, and reported fossils to museum staff as he found them over the years. Jaw fragments and teeth eroding from the hillside led to the discovery of the dromaeosaur specimen; Marshall collected the loose fossil fragments and delivered them to the palaeontologist Philip J. Currie at the museum, and the remaining parts were later collected. The specimen was in an isolated block of sandstone that was relatively hard, and preparation revealed the right maxilla (main bone of the upper jaw) exposed in outer side-view and the right dentary (tooth-bearing bone of the lower jaw) exposed in inner side view, and both of these bones were left in the block.[1][2][3]

In 2004, Currie and the palaeontologist David Varricchio made the specimen (catalogued as RTMP 95.166.1) the holotype of the new genus and species Atrociraptor marshalli. The generic name is derived from the Latin words atroci, which means "savage", and raptor, Latin for "robber". The specific name references Marshall, the discoverer. The full name means “Wayne Marshall’s savage robber”. Since then, Marshall led the museum staff to many important finds. In all, the holotype preserves both premaxillae (frontmost bone of the upper jaw, freed from the rock matrix), a right maxilla, both dentaries (the left one is incomplete), associated teeth, and numerous bone fragments from the skull.[1][2] A number of isolated teeth (previously referred to Saurornitholestes) have also been recovered from the Horseshoe Canyon Formation;[4] they can be recognized by their unusually large serrations.

Description[edit]

Size compared to a human

Atrociraptor was a relatively small dromaeosaurine, comparable to Velociraptor in size, and is estimated to have measured about 1.80–2 m (5.9–6.6 ft) in length and weighed 15 kg (33 lb). As a dromaeosaur, it would have had large arms, a long tail with ossified tendons, and a large sickle-claw on the robust, hyper-extendible second toe.[5][6] Fossils of other dromaeosaurs, such as Zhenyuanlong, show that even relatively large members of the group had pennaceous feathers, with large wings on the arms and long feathers on the tail.[7]

Hypothetical life restoration with body and plumage based on related dromaeosaurids

Atrociraptor differs from Bambiraptor and other Dromaeosaurids in its more isodont dentition—the teeth have different sizes but the same form—and short deep snout. A skull opening, the maxillary fenestra, is relatively large and positioned right above another opening, the premaxillary fenestra, a condition not known from other species. The skull appears to have been unusually short and tall. The teeth are relatively straight, but they emerge from the tooth sockets at an angle to the jaw line, resulting in a strongly raked row of teeth.

Classification[edit]

Reconstructed skeleton of the related Bambiraptor, which represents a juvenile saurornitholestine

When Atrociraptor was first described, it was assigned to the subfamily Velociraptorinae, a group known predominantly from the Late Cretaceous of Asia. This assignment was based on the difference in size between the anterior and posterior serrations on the maxillary teeth and the size of the second premaxillary tooth.[1] This assignment was contested by Nick Longrich and Phil Currie in a 2009 analysis, which grouped it as a close relative of Saurornitholestes as part of a new subfamily: Saurornitholestinae.[8]

The uncertainty around the classification of Atrociraptor would not be resolved for some time. In their description of Acheroraptor, David Evans and colleagues suggested that Atrociraptor was the sister taxon of the much older genus Deinonychus in a clade more derived than Saurornitholestinae but outside of both Velociraptorinae and Dromaeosaurinae. Notably, this analysis used the same phylogenetic data set as the earlier analysis by Longrich and Currie, but included more taxa which had been described in the interim. In this analysis, the taxon they were describing, Acheroraptor, was found to be a velociraptorine, although this would also be contested in the future.[9] The analysis that accompanied the description of Dakotaraptor by Robert DePalma and colleagues recovered Atrociraptor as a member of Dromaeosaurinae, alongside Deinonychus, although there is no explanation in the description for this recovered classification.[10]

Modern dromaeosaurid systematics is dominated by a few phylogenetic datasets which recover slightly different results. One of the most widespread is the so-called "TWiG matrix" (named for the Theropod Working Group), developed by Steven Brusatte, Andrea Cau, Mark Norell, and several other researchers, which contains data for a wide number of coelurosaur taxa and is updated regularly by new authors.[11] Other matrices include the matrix published by Mark Powers,[12] the matrix published by Scott Hartman and colleagues,[13] and one produced by Phil Currie and David Evans.[14] In many of the most updated analyses for each of these matrices, including data from recently described taxa, Atrociraptor has been consistently recovered as a member of Saurornitholestinae.[15][14][8][16][17][18] The results of these analyses, including one of the most recent iterations of the various data sets, are shown below.

Evans, Larson, & Currie 2013[9]
Eudromaeosauria
Czepiński 2022[15]
Eudromaeosauria

Palaeobiology[edit]

The paleontologist Gregory S. Paul suggested in 2016 that Atrociraptor was able to attack relatively large prey, and wounding it more than usual for its relatives with its strong head and teeth. As a dromaeosaur, it would have used its sickle claw to deal with its prey.[6]

Palaeoecology[edit]

Contemporary dinosaurs of the Horseshoe Canyon Formation

Paleoenvironment[edit]

The holotype remains of Atrociraptor were found at a locality about 5 kilometres (3.1 mi) West of the Royal Tyrrell Museum of Paleontology.[1][19] This locality is part of the Horsthief Member of the Horseshoe Canyon Formation, which is the second-oldest member of the formation. The Horsethief Member ranges from around 72.2—71.5 million years ago, a timespan of about 700,000 years.[20] Teeth from elsewhere in the Horseshoe Canyon Formation have been referred to Atrociraptor. If these referrals are valid, it would mean Atrociraptor had a much wider geographic and temporal distribution than initially suggested. These remains push the latest occurance of Atrociraptor to the Tolman Member of the formation (about 70.9-69.6 million years ago), suggesting the genus may have existed for over 2 million years.[21][22]

In the early Maastrichtian, the continent of Laramidia (today North America) was about 8 degrees further North than North America is today.[19] Despite this, the average temperature of the area was almost certainly much warmer than the region is today. The mean annual temperature in the Early Maastrichtian is estimated to have been around 10 °C (50 °F),[23] compared to 4.5 °C (40.1 °F) today.[24]

The lower part of the Horseshoe Canyon Formation, where Atrociraptor was discovered, corresponds to "poorly-drained" sediments rich with organic material. The sediments of the Horsetheif Member are composed primarily of coal, shale which is high in organic material, sandstones, and a small number of mudstones. These are reflective of a highly saturated environment, likely a coastal plain or fluvial system which was on the margins of the Western Interior Seaway.[25] This suggests that the region was very humid and composed primarily of wetlands with a high water table. This is futher corroborated by the presence of a wider variety of turtles in the lower members of the formation than in the higher members.[23]

As the Maastrichtian stage progressed, the Western Interior Seaway began to shrink, which is reflected in the paleoclimatic reconstructions of the region. Later sediments are believed to have been further inland and less humid than those of the Late Campanian.[23] This may be responsible for the apparent change in fauna during this period.[26] How these climatic changed affected Atrociraptor is not clear, due to the rarity of its remains, but the discovery of teeth from the geologically younger Tolman Member suggests that the taxon may have survived through this period.[21] However, it is known that major flooding events continued throughout this period. A bonebed in Dry Island Buffalo Jump Provincial Park, dated to one of the upper members of the Horseshoe Canyon Formation, preserves several Albertosaurus individuals, which are believed to have been killed and buried during a major storm.[27]

Despite the regression of the Western Interior Seaway, Cretaceous Alberta became wetter and more humid in the uppermost part of the formation (around 68 million years ago). Atrociraptor remains are not known from these youngest sediments, which suggests that the change in climate forced the small theropod to either move elsewhere or else become extinct.[26]

Contemporary fauna[edit]

The Horsethief Member of the Horseshoe Canyon Formation constitutes the upper part of the so-called "Edmontosaurus regalis-Pachyrhinosaurus canadensis dinosaur zone". As the name suggests, two common terrestrial herbivores in these lower strata were Pachyrhinosaurus and Edmontosaurus. The lower part of Horseshoe Canyon has also preserves fossils of other ceratopsids including Anchiceratops, Arrhinoceratops, and several indeterminate specimens. Ankylosaurs are also well-represented in this member. The genera Edmontonia and Anodontosaurus have been found alongside indeterminate ankylosaur remains. Hadrosaurid remains are very common, but many of these are not confidently referred to any genera besides Edmontosaurus. Fragmentary remains of pachycephalosaurids have also been found.[20]

Theropod remains are also common in the Horsetheif Member. Ornithomimus and Struthiomimus are known from several specimens, and other coelurosaurs are known from a few remains. These included the troodontid Albertavenator and the caenagnathids Apatoraptor and Epichirostenotes. Although their remains are not known directly from the Horsetheif Member, Dromaeosaurus, Paronychodon, and the tooth-taxon Richardoestesia are known from both older and younger deposits, so they are inferred to have existed at this time as well. The largest theropod in the Horsethief Member (and the Horseshoe Canyon Formation generally) was the tyrannosaurid Albertosaurus.[20]

Remains of smaller animals are also common in the Horseshoe Canyon. Fish are common fossils and are represented by sclerorhynchoids, guitarfish, sturgeons, paddlefishes, aspidorhynchids, osteoglossomorphs, elopiformes, ellimmichthyiformes, esocids, and acanthomorphs. Frogs and salamanders are also known from teeth found in these deposits alongside polyglyphanodontian lizards.[26] Turtles were also very diverse in the warm and humid climate of the Early Maastrichtian. Fossils of macrobaenids, chelydrids, trionychids, adocids, and the giant genus Basilemys have been found from the parts of Horseshoe Canyon that correspond to wetlands.[23] The choristodere genus Champsosaurus was also a resident of Alberta during this time.[26]

The holotype of Atrociraptor is the only fossil discovered from its locality, so it is not known for certain if any of these animals directly coexisted with it, but many of them are known to have been contemporaneous.[19]

See also[edit]

References[edit]

  1. ^ a b c d e Currie, P. J. and D. J. Varricchio (2004). "A new dromaeosaurid from the Horseshoe Canyon Formation (Upper Cretaceous) of Alberta, Canada". Pp. 112–132 in P. J. Currie, E. B. Koppelhus, M. A. Shugar and J. L. Wright. (eds.), Feathered Dragons. Indianapolis: Indiana University Press. [1]
  2. ^ a b Majeski, Jared (3 August 2022). "Stories of discovery: the Savage Robber". RETROactive. Historic Resources Management Branch of Alberta Culture, Multiculturalism and Status of Women. Retrieved 17 July 2024.
  3. ^ Hutchison, Jim; Pfeiff, Margo (8 July 1990). "Dig This: Canada's Fertile Dinosaur Country Still Has Plenty of Well-Preserved Bones to Pick". Los Angeles Times. Retrieved 17 July 2024.
  4. ^ Ryan, M. J., P. J. Currie, et al. (1998). "Baby hadrosaurid material associated with an unusually high abundance of Troodon teeth from the Horseshoe Canyon Formation, Upper Cretaceous, Alberta, Canada". Gaia 16: 123–133
  5. ^ Holtz, T. R. Jr. (2012). Dinosaurs: The Most Complete, Up-to-date Encyclopedia for Dinosaur Lovers of All Ages. New York: Random House. p. 158, 384. ISBN 978-0-375-82419-7.
  6. ^ a b Paul, G.S. (2016). The Princeton Field Guide to Dinosaurs (2 ed.). Princeton: Princeton University Press. pp. 146, 151. ISBN 978-0-691-16766-4.
  7. ^ Lü, Junchang; Brusatte, Stephen L. (2015). "A large, short-armed, winged dromaeosaurid (Dinosauria: Theropoda) from the Early Cretaceous of China and its implications for feather evolution". Scientific Reports. 5 (1). doi:10.1038/srep11775.
  8. ^ a b Longrich, N.R.; Currie, P.J. (2009). "A microraptorine (Dinosauria–Dromaeosauridae) from the Late Cretaceous of North America". PNAS. 106 (13): 5002–7. Bibcode:2009PNAS..106.5002L. doi:10.1073/pnas.0811664106. PMC 2664043. PMID 19289829.
  9. ^ a b 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.
  10. ^ 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). doi:10.17161/paleo.1808.18764.
  11. ^ Napoli, J. G.; Ruebenstahl, A. A.; Bhullar, B.-A. S.; Turner, A. H.; Norell, M. A. (2021). "A New Dromaeosaurid (Dinosauria: Coelurosauria) from Khulsan, Central Mongolia" (PDF). American Museum Novitates (3982): 1–47. doi:10.1206/3982.1. hdl:2246/7286. ISSN 0003-0082. S2CID 243849373.
  12. ^ Powers, Mark J.; Fabbri, Matteo; Doschak, Michael R.; Bhullar, Bhart-Anjan S.; Evans, David C.; Norell, Mark A.; Currie, Philip J. (2021). "A new hypothesis of eudromaeosaurian evolution: CT scans assist in testing and constructing morphological characters". Journal of Vertebrate Paleontology. 41 (5). Bibcode:2021JVPal..41E0087P. doi:10.1080/02724634.2021.2010087.
  13. ^ Hartman, S.; Mortimer, M.; Wahl, W.R.; Lomax, D.R.; Lippincott, J.; Lovelace, D.M. (2019). "A new paravian dinosaur from the Late Jurassic of North America supports a late acquisition of avian flight". PeerJ. 7: e7247. doi:10.7717/peerj.7247. PMC 6626525. PMID 31333906.
  14. ^ a b 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: ar.25103. doi:10.1002/ar.25103. ISSN 1932-8486. PMID 36342817. S2CID 253382718.
  15. ^ a b 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. S2CID 259441055.
  16. ^ 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. doi:10.1080/02724634.2021.2010087. S2CID 247039404.
  17. ^ Chiarenza, Alfio Alessandro; Fiorillo, Anthony R.; Tykoski, Ronald S.; McCarthy, Paul J.; Flaig, Peter P.; Contreras, Dori L. (2020). "The first juvenile dromaeosaurid (Dinosauria: Theropoda) from Arctic Alaska". PLOS ONE. 15 (7): e0235078. Bibcode:2020PLoSO..1535078C. doi:10.1371/journal.pone.0235078. PMC 7343144. PMID 32639990.
  18. ^ Pittman, Michael; Xu, Xing (2020). "Pennaraptoran Theropod Dinosaurs Past Progress and New Frontiers". Bulletin of the American Museum of Natural History. 440 (1): 1. doi:10.1206/0003-0090.440.1.1.
  19. ^ a b c Carrano, Matthew (2009). "5 km west of Royal Tyrrell Museum (Cretaceous of Canada)". The Paleobiology Database. Where: Alberta, Canada (51.5° N, 112.8° W: paleocoordinates 59.2° N, 84.6° W)
  20. ^ a b c Eberth, David A.; Kamo, Sandra (2019). "High-precision U-Pb CA-ID-TIMS dating and chronostratigraphy of the dinosaur-rich Horseshoe Canyon Formation (Upper Cretaceous, Campanian–Maastrichtian), Red Deer River valley, Alberta, Canada". Canadian Journal of Earth Sciences. 57 (10): 1220–1237. Bibcode:2020CaJES..57.1220E. doi:10.1139/cjes-2019-0019. S2CID 210299227.
  21. ^ a b Larson, Derek W.; Currie, Philip J. (2013). "Multivariate Analyses of Small Theropod Dinosaur Teeth and Implications for Paleoecological Turnover through Time". PLOS ONE. 8 (1): e54329. Bibcode:2013PLoSO...854329L. doi:10.1371/journal.pone.0054329. PMC 3553132. PMID 23372708.
  22. ^ Tanke, Darren H.; Currie, Philip J. (2010). "A history of Albertosaurus discoveries in Alberta, Canada". Canadian Journal of Earth Sciences. 47 (9): 1197–1211.
  23. ^ a b c d Quinney, Annie; Therrien, François; Zelenitsky, Darla K.; Eberth, David A. (2013). "Palaeoenvironmental and palaeoclimatic reconstruction of the Upper Cretaceous (late Campanian–early Maastrichtian) Horseshoe Canyon Formation, Alberta, Canada". Palaeogeography, Palaeoclimatology, Palaeoecology. 371: 26–44. Bibcode:2013PPP...371...26Q. doi:10.1016/j.palaeo.2012.12.009.
  24. ^ "Drumheller Climate (Canada)". Climate Data. 2024. The average annual temperature is 4.5 °C.
  25. ^ Eberth, David A.; Braman, Dennis R. (September 2012). "A revised stratigraphy and depositional history for the Horseshoe Canyon Formation (Upper Cretaceous), southern Alberta plains". Canadian Journal of Earth Sciences. 49 (9): 1053–1086. Bibcode:2012CaJES..49.1053E. doi:10.1139/e2012-035. ISSN 0008-4077.
  26. ^ a b c d Larson, Derek W.; Brinkman, Donald B.; Bell, Phil R. (2010). "Faunal assemblages from the upper Horseshoe Canyon Formation, an early Maastrichtian cool-climate assemblage from Alberta, with special reference to the Albertosaurus sarcophagus bonebed". Canadian Journal of Earth Sciences. 47 (9): 1159–1181. Bibcode:2010CaJES..47.1159L. doi:10.1139/E10-005.
  27. ^ Eberth, David A.; Currie, Philip J. (2010). "Stratigraphy, sedimentology, and taphonomy of the Albertosaurus bonebed (Upper Horseshoe Canyon Formation; Maastrichtian), southern Alberta, Canada". Canadian Journal of Earth Sciences. 47 (9): 1119–1143. doi:10.1139/E10-045.
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