Edmontonia

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Edmontonia
Temporal range: Late Cretaceous, 76.5–66Ma
Edmontonia half.jpg
Mounted skeleton of E. rugosidens, specimen AMNH 5665
Scientific classification e
Kingdom: Animalia
Phylum: Chordata
Clade: Dinosauria
Order: Ornithischia
Family: Nodosauridae
Genus: Edmontonia
Sternberg, 1928
Species
  • E. longiceps Sternberg, 1928 (type)
  • E. rugosidens (Gilmore, 1930 [originally Palaeoscincus rugosidens])
  • E. schlessmani (Bakker, 1988 [originally Denversaurus schlessmani])
Synonyms
  • Denversaurus Bakker, 1988
  • Chassternbergia Bakker, 1988

Edmontonia was an armoured dinosaur, a part of the nodosaur family from the Late Cretaceous Period. It is named after the Edmonton Formation (now the Horseshoe Canyon Formation), the unit of rock it was found in.

Description[edit]

Size and general build[edit]

Restored skeleton without dermal armour

Edmontonia was bulky, broad and tank-like. Its length has been estimated at six to seven meters.[1] In 2010, Gregory S. Paul considered both main Edmontonia species, E. longiceps and E. rugosidens, to be equally long at six metres and weigh three tonnes.[2]

Edmontonia had small, oval ridged bony plates on its back and head and many sharp spikes along its sides. The four largest spikes jutted out from the shoulders on each side, two of which were split into subspines in some E. rugosidens specimens.[3] Its skull had a pear-like shape when viewed from above.[3] Its neck and shoulders were protected by three halfrings made of large keeled plates.

Distinguishing traits[edit]

In 1990, Kenneth Carpenter established some diagnostic traits for the genus as whole, mainly comparing it with its close relative Panoplosaurus. In top view, the snout has more parallel sides. The skull armour has a smooth surface. In the palate, the vomer is keeled. The neural arches and neural spines are shorter than those of Panoplosaurus. The sacrum proper consists of three sacral vertebrae. In the shoulder girdle, the scapula and coracoid are not fused.[4]

Carpenter also indicated in which way the main species differed from each other. The type species, Edmontonia longiceps, is distinguished from E. rugosidens in lacking sideways projecting osteoderms behind the eye sockets; having tooth rows that are less divergent; possessing a more narrow palate; having a sacrum that is wider than long and more robust; and in having shorter spikes at the sides. Also, an ossified cheek plate, known from E. rugosidens specimens, has not been found with Edmontonia longiceps.[4]

Skeleton[edit]

The skull of Edmontonia, up to half a metre long, is somewhat elongated with a protruding truncated snout. The snout carried a horny upper beak and the front snout bones, the premaxillae, were toothless. In the sides of the snout large depressions were present, "nasal vestibules", that each possessed two smaller openings. The top of these was a horizontal oval and represented the bony external nostril, the entrance to the nasal cavity, the normal air passage. The more rounded second opening below and obliquely in front, was the entrance to a "paranasal" tract, running along the outer side of the nasal cavity, in a somewhat lower position. A study by Matthew Vickaryous in 2006 proved for the first time the presence of multiple openings with a nodosaurid; such structures had already been well established in ankylosaurids. The air tracts are however, much simpler than in the typical ankylosaurid condition, and are not convoluted while lacking bony turbinate bones. The nasal cavity is separated into two halves along the midline by a bone wall. This septum is continued to below by the vomers, which are keeled, the keel featuring a pendulum-shaped appendage.[5] Another similarity with Ankylosauridae is the presence of a secondary bone palate, a possible case of parallel evolution. This has been shown too for Panoplosaurus.

Discovery and species[edit]

The AMNH 5381 specimen of E. rugosidens, 1915 (first referred to Palaeoscincus by Matthew in 1922), showing the position of the dermal armour

In 1915, the American Museum of Natural History obtained the nearly complete, articulated front half of an armoured dinosaur, found the same year by Barnum Brown in Alberta, Canada. In 1922, William Diller Matthew referred this specimen, AMNH 5381, to Palaeoscincus in a popular-science article, not indicating any particular species.[6] It had been intended to name a new Palaeoscincus species in cooperation with Brown but their article was never published.[4] Matthew also referred specimen AMNH 5665, the front of a skeleton found by Levi Sternberg in 1917. In 1930 Charles Whitney Gilmore referred both specimens to Palaeoscincus rugosidens.[7] This species was based on type specimen USNM 11868, a skeleton found by George Fryer Sternberg in June 1928. The specific name is derived from Latin rugosus, "rough", and dens, "tooth". In 1940, Lori Shano Russell referred all three specimens to Edmontonia, as an Edmontonia rugosidens.[8]

Meanwhile, the type species of Edmontonia, Edmontonia longiceps, had been named by Charles Mortram Sternberg in 1928. The generic name Edmontonia refers to Edmonton or the Edmonton Formation. The specific name longiceps means "long-headed" in Latin. Its holotype is specimen NMC 8531, consisting of a skull, right lower jaw and much of the postcranial skeleton, including the armour. It was discovered near Morrin in 1924 by George Paterson, the teamster of the expedition led by C.M. Sternberg.[9]

Edmontonia species include:

left side of E. rugosidens specimen AMNH 5665
  • E. rugosidens. This species has been given its own genus, Chassternbergia, first coined as a subgenus by Dr. Robert Thomas Bakker in 1988, as Edmontonia (Chassternbergia) rugosidens and is based on differences in skull proportion from E. longiceps and its earlier time period.[11][12] It was given its full generic name in 1991 by George Olshevsky.[13] The name Chassternbergia honours Charles, "Chas", M. Sternberg. This subgenus or genus name is rarely applied.[14][1] E. rugosidens is found in the Campanian lower Dinosaur Park Formation, dating from about 76.5-75 million years ago.[10] Many later finds have been referred to E. rugosidens, among them CMN 8879, the top of a skull found in 1937 by Harold D'acre Robinson Lowe; ROM 433, a forked spine found by Jack Horner in 1986 among Oohkotokia material; ROM 5340, paired medial plates; ROM 1215, a skeleton; RTMP 91.36.507, a skull; RTMP 98.74.1, a possible Edmontonia skull; RTMP 98.71.1, a skeleton;[15] RTMP 98.98.01, a skull and right lower jaw; and RTMP 2001.12.158, a skull.[16]
  • E. australis, the "southern one", named by Tracy Lee Ford in 2000 and known from cervical scutes only. Among them is the holotype NMMNH P-25063, a pair of medial keeled neck osteoderms from the Maastrichtian Kirtland Formation of New Mexico and the paratype NMMNH P-27450, a right middle neck plate.[12] It is often considered to be a dubious name[14] or a synonym of Glyptodontopelta mimus.[17]
  • E. schlessmani, a renaming in 1992 of Denversaurus schlessmani ("Schlessman's Denver lizard") by Adrian Hunt and Spencer Lucas.[18] This taxon was erected by Bakker in 1988 for a skull from the Late Maastrichtian Upper Cretaceous Lance Formation of South Dakota, specimen DMNH 468 found by Philip Reinheimer in 1922. This type specimen of Denversaurus is in the collections of the Denver Museum of Natural History (now the Denver Museum of Nature and Science), Denver, Colorado for which the genus was named. The specific name honours Lee E. Schlessman, whose Schlessman Family Foundation sponsored the museum. Bakker described the skull as being much wider at the rear than Edmontonia specimens.[11] However, later workers explained this by its being crushed,[4] and considered the taxon a junior synonym of Edmontonia longiceps.[1] The Black Hills Institute has referred a skeleton from the Lance Formation to Denversaurus, nicknamed "Tank". It has the inventory number BHI 127327.[19]

The naming history was further complicated in 1971, when Walter Preston Coombs Jr renamed both Edmontonia species, into Panoplosaurus longiceps and Panoplosaurus rugosidens respectively.[20] The latter species, which due to its much more complete material has determined the image of Edmontonia, until 1940 thus appeared under the name of Palaeoscincus, and during the 1970s and 1980s was shown as "Panoplosaurus" until newer research revived the name Edmontonia.

Paleobiology[edit]

Life restoration of two E. rugosidens from 1922, based on the 1915 AMNH specimen

The large spikes were probably used between males in contests of strength to defend territory or gain mates.[3] The spikes would also have been useful for intimidating predators or rival males, passive protection, or for active self-defense.[3] The large forward pointing shoulder spikes could have been used to run through attacking theropods. Carpenter suggested that the larger spikes of AMNH 5665 indicated this was a male specimen, a case of sexual dimorphism. However, he admitted the possibility of ontogeny, older individuals having longer spikes, as the specimen was relatively large.[4] Traditionally it had been assumed that to protect themselves from predators, nodosaurids like Edmontonia might have crouched down on the ground to minimize the possibility of attack to their defenseless underbelly.

Rings in the petrified wood of trees contemporary with Edmontonia show evidence of strong seasonal changes in precipitation and temperature;[3] this may hold an explanation for why so many specimens have been found with their armor plating and spikes in the same position they were in life.[3] The Edmontonia could have died due to drought, dried up, and then rapidly became covered in sediment when the rainy season began.[3]

Paleoecology[edit]

Skeletons of E. schlessmani and the Tyrannosaurus nicknamed "Wyrex", Houston Museum of Natural Science

Edmontonia rugosidens existed in the upper section of the Dinosaur Park Formation, about 76.5–75 million years ago. It lived alongside numerous other giant herbivores, such as the hadrosaurids Gryposaurus, Corythosaurus and Parasaurolophus, the ceratopsids Centrosaurus and Chasmosaurus, and ankylosaurids Scolosaurus[10] and Dyoplosaurus[10] Studies of the jaw anatomy and mechanics of these dinosaurs suggests they probably all occupied slightly different ecological niches in order to avoid direct competition for food in such a crowded eco-space.[21] The only large predators known from the same levels of the formation as Edmontonia are the tyrannosaurids Gorgosaurus libratus and an unnamed species of Daspletosaurus.[10]

Edmontonia longiceps is known from the Horseshoe Canyon Formation, from the middle unit, which was dated to 71.5-71 million years ago in 2009.[10]The fauna of the Horseshoe Canyon Formation is well-known, as vertebrate fossils, including those of dinosaurs, are quite common. Sharks, rays, sturgeons, bowfins, gars and the gar-like Aspidorhynchus made up the fish fauna. Mammals included multituberculates and the marsupial Didelphodon. The saltwater plesiosaur Leurospondylus has been found in marine sediments in the Horseshoe Canyon, while freshwater environments were populated by turtles, Champsosaurus, and crocodilians like Leidyosuchus and Stangerochampsa. Dinosaurs dominate the fauna, especially hadrosaurs, which make up half of all dinosaurs known, including the genera Edmontosaurus, Saurolophus and Hypacrosaurus. Ceratopsians and ornithomimids were also very common, together making up another third of the known fauna. Along with much rarer ankylosaurians and pachycephalosaurs, all of these animals would have been prey for a diverse array of carnivorous theropods, including troodontids, dromaeosaurids, and caenagnathids.[22][23] Adult Albertosaurus was the apex predator in this environment, with intermediate niches possibly filled by juvenile albertosaurs.[22]

References[edit]

  1. ^ a b c Vickaryous, M.K., Maryańska, T., and Weishampel, D.B., (2004). "Ankylosauria". In Weishampel, D. B., Dodson, P., and Osmólska, H. (eds.). The Dinosauria (Second Edition). University of California Press. pp. 363–392. ISBN 0-520-24209-2. 
  2. ^ Paul, G.S., 2010, The Princeton Field Guide to Dinosaurs, Princeton University Press p. 238
  3. ^ a b c d e f g "Edmontonia." In: Dodson, Peter & Britt, Brooks & Carpenter, Kenneth & Forster, Catherine A. & Gillette, David D. & Norell, Mark A. & Olshevsky, George & Parrish, J. Michael & Weishampel, David B. The Age of Dinosaurs. Publications International, LTD. p. 141. ISBN 0-7853-0443-6.
  4. ^ a b c d e Carpenter, K. 1990. "Ankylosaur systematics: example using Panoplosaurus and Edmontonia (Ankylosauria: Nodosauridae)", In: Carpenter, K. & Currie, P.J. (eds) Dinosaur Systematics: Approaches and Perspectives, Cambridge University Press, Cambridge, pp. 281-298
  5. ^ Matthew K. Vickaryous, 2006, "New information on the cranial anatomy of Edmontonia rugosidens Gilmore, a Late Cretaceous nodosaurid dinosaur from Dinosaur Provincial Park, Alberta", Journal of Vertebrate Paleontology, 26(4): 1011-1013
  6. ^ Matthew, W. D. 1922. A superdreadnaught of the animal world—the armoured dinosaur Palaeoscincus. Natural History 22: 333-342.
  7. ^ C.W. Gilmore, 1930, "On dinosaurian reptiles from the Two Medicine Formation of Montana", Proceedings of the United States National Museum 77(16): 1-39
  8. ^ Russell, L.S. 1940. Edmontonia rugosidens (Gilmore), an armored dinosaur from the Belly River Series of Alberta. University of Toronto Studies, Geology Series 43: 3-2.
  9. ^ C.M. Sternberg, 1928, "A new armored dinosaur from the Edmonton Formation of Alberta", Transactions of the Royal Society of Canada, series 3 22: 93-106
  10. ^ a b c d e f Arbour, V. M.; Burns, M. E.; Sissons, R. L. (2009). "A redescription of the ankylosaurid dinosaur Dyoplosaurus acutosquameus Parks, 1924 (Ornithischia: Ankylosauria) and a revision of the genus". Journal of Vertebrate Paleontology 29 (4): 1117–1135. doi:10.1671/039.029.0405. 
  11. ^ a b Bakker, R.T. (1988). Review of the Late Cretaceous nodosauroid Dinosauria: Denversaurus schlessmani, a new armor-plated dinosaur from the Latest Cretaceous of South Dakota, the last survivor of the nodosaurians, with comments on Stegosaur-Nodosaur relationships. Hunteria 1(3):1-23.(1988).
  12. ^ a b Ford, T.L. (2000). A review of ankylosaur osteoderms from New Mexico and a preliminary review of ankylosaur armor. In: Lucas, S.G., and Heckert, A.B. (eds.). Dinosaurs of New Mexico. New Mexico Museum of Natural History and Science Bulletin 17:157-176.
  13. ^ G. Olshevsky, 1991, A revision of the parainfraclass Archosauria Cope, 1869, excluding the advanced Crocodylia, Mesozoic Meanderings 2, 268 pp
  14. ^ a b Carpenter K (2001). "Phylogenetic analysis of the Ankylosauria". In Carpenter, Kenneth(ed). The Armored Dinosaurs. Indiana University Press. pp. 455–484. ISBN 0-253-33964-2. 
  15. ^ Currie P.J., Russell D.A., 2005, "The geographic and stratigraphic distribution of articulated and associated dinosaur remains", In: Currie P.J., Koppelhus E.B., (editors). Dinosaur Provincial Park: A spectacular ancient ecosystem revealed. Bloomington: Indiana University Press. pp 537–569
  16. ^ Matthew K. Vickaryous, 2006, "New information on the cranial anatomy of Edmontonia rugosidens Gilmore, a Late Cretaceous nodosaurid dinosaur from Dinosaur Provincial Park, Alberta", Journal of Vertebrate Paleontology, 26(4): 1011-1013
  17. ^ Burns, Michael E. (2008). "Taxonomic utility of ankylosaur (Dinosauria, Ornithischia) osteoderms: Glyptodontopelta mimus Ford, 2000: a test case". Journal of Vertebrate Paleontology 28 (4): 1102–1109. doi:10.1671/0272-4634-28.4.1102. 
  18. ^ Hunt, A.P. and Lucas, S.G., 1992, "Stratigraphy, Paleontology and age of the Fruitland and Kirkland Formations (Upper Cretaceous), San Juan Basin, New Mexico", New Mexico Geological Society Guidebook, 43rd Field Conference, San Juan Basin, volume 4, p. 217-240
  19. ^ Carpenter K., DiCroce T., Kinneer B., Simon R., 2013, "Pelvis of Gargoyleosaurus (Dinosauria: Ankylosauria) and the Origin and Evolution of the Ankylosaur Pelvis", PLoS ONE 8(11): e79887. doi:10.1371/journal.pone.0079887
  20. ^ Coombs, W.P. Jr., 1971, The Ankylosauria, Dissertaton Columbia University, New York, 487 pp
  21. ^ Mallon, J. C., Evans, D. C., Ryan, M. J., & Anderson, J. S. (2012). Megaherbivorous dinosaur turnover in the Dinosaur Park Formation (upper Campanian) of Alberta, Canada. Palaeogeography, Palaeoclimatology, Palaeoecology.
  22. ^ a b Eberth, D.A., 1997, "Edmonton group". In: Currie, P.J., Padian, K. (Eds.), Encyclopedia of Dinosaurs. Academic Press, New York, pp. 199–204
  23. ^ 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: 1159–1181.