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==Description==
==Description==
[[File:ElasmosaurusDB15.jpg|thumb|left|Restoration with size comparison]]
[[File:ElasmosaurusDB15.jpg|thumb|left|Restoration with size comparison]]
At {{convert|10.3|m}} in length,<ref name="gorman2016">{{cite journal | first1 = J.P. | last1 = O'Gorman | title = A Small Body Sized Non-Aristonectine Elasmosaurid (Sauropterygia, Plesiosauria) from the Late Cretaceous of Patagonia with Comments on the Relationships of the Patagonian and Antarctic Elasmosaurids | journal = Ameghiniana | volume = 53 | issue = 3 | pages = 245-268 | url = http://www.bioone.org/doi/abs/10.5710/AMGH.29.11.2015.2928 | doi = 10.5710/AMGH.29.11.2015.2928 | year = 2016}}</ref> ''Elasmosaurus'' was among the largest plesiosaurs. It differs from all other plesiosaurs by having six teeth per [[premaxilla]] (the bones at the tip of the snout) and 72 [[cervical vertebrae|neck]] (cervical) [[vertebra]]e.<ref name=Sachs2005>{{cite journal|author=Sachs, S.|year=2005|title=Redescription of ''Elasmosaurus platyurus'', Cope 1868 (Plesiosauria: Elasmosauridae) from the Upper Cretaceous (lower Campanian) of Kansas, U.S.A|journal=Paludicola|volume=5|issue=3|pages=92-106|url=https://www.researchgate.net/publication/260421820_Redescription_of_Elasmosaurus_platyurus_Cope_1868_Plesiosauria_Elasmosauridae_from_the_Upper_Cretaceous_Lower_Campanian_of_Kansas_USA}}</ref> The skull was relatively flat, with a number of long pointed teeth. The lower jaws were joined at the tip to a point between the fourth and fifth teeth.<ref name=Sachs2005/> The neck vertebrae immediately following the skull were long and low, and had longitudinal lateral crests.<ref name=Brown1993>Brown, D. S. 1993. "A taxonomic reappraisal of the families Elasmosauridae and Cryptoclididae (Reptilia: Plesiosauroidea)". ''Révue de Paléobiologie'', Volume Spécial, 7, 9-16.</ref><ref name=Carpenter1999>{{cite journal|author=Carpenter, K.|year=1999|title=Revision of North American elasmosaurs from the Cretaceous of the western interior|journal=Paludicola|volume=2|issue=2|pages=148-173}}</ref> Like most elasmosaurids, ''Elasmosaurus'' had around three pectoral vertebrae. The tail included at least 18 vertebrae.<ref name=Brown1993/><ref name=Carpenter1999/>
At {{convert|10.3|m}} in length,<ref name="gorman2016">{{cite journal | first1 = J.P. | last1 = O'Gorman | title = A Small Body Sized Non-Aristonectine Elasmosaurid (Sauropterygia, Plesiosauria) from the Late Cretaceous of Patagonia with Comments on the Relationships of the Patagonian and Antarctic Elasmosaurids | journal = Ameghiniana | volume = 53 | issue = 3 | pages = 245-268 | url = http://www.bioone.org/doi/abs/10.5710/AMGH.29.11.2015.2928 | doi = 10.5710/AMGH.29.11.2015.2928 | year = 2016}}</ref> ''Elasmosaurus'' was among the largest plesiosaurs. It differs from all other plesiosaurs by having six teeth per [[premaxilla]] (the bones at the tip of the snout) and 72 [[cervical vertebrae|neck]] (cervical) [[vertebra]]e.<ref name=Sachs2005>{{cite journal|author=Sachs, S.|year=2005|title=Redescription of ''Elasmosaurus platyurus'', Cope 1868 (Plesiosauria: Elasmosauridae) from the Upper Cretaceous (lower Campanian) of Kansas, U.S.A|journal=Paludicola|volume=5|issue=3|pages=92-106|url=https://www.researchgate.net/publication/260421820_Redescription_of_Elasmosaurus_platyurus_Cope_1868_Plesiosauria_Elasmosauridae_from_the_Upper_Cretaceous_Lower_Campanian_of_Kansas_USA}}</ref> Only ''[[Albertonectes]]'', with its 75 vertebrate, is known to have had more. The two genera have the highest numbers of cervical vertebrae for vertebrates.<ref>{{cite journal|author=Sach, S.; Kear, B. P.; Everhart, M.|year=2013|title=Revised Vertebral Count in the "Longest-Necked Vertebrate" ''Elasmosaurus platyurus'' Cope 1868, and Clarification of the Cervical-Dorsal Transition in Plesiosauria|journal=PLoS ONE|volume=8|issue=8|page=e70877|doi=10.1371/journal.pone.0070877}}</ref> The skull was relatively flat, with a number of long pointed teeth. The lower jaws were joined at the tip to a point between the fourth and fifth teeth.<ref name=Sachs2005/> The neck vertebrae immediately following the skull were long and low, and had longitudinal lateral crests.<ref name=Brown1993>{{cite journal|author=Brown, D. S.|year=1993|title=A taxonomic reappraisal of the families Elasmosauridae and Cryptoclididae (Reptilia: Plesiosauroidea)|journal=Révue de Paléobiologie|volume=7|pages=9-16}}</ref><ref name=Carpenter1999>{{cite journal|author=Carpenter, K.|year=1999|title=Revision of North American elasmosaurs from the Cretaceous of the western interior|journal=Paludicola|volume=2|issue=2|pages=148-173}}</ref> Like most elasmosaurids, ''Elasmosaurus'' had around three pectoral vertebrae. The tail included at least 18 vertebrae.<ref name=Brown1993/><ref name=Carpenter1999/>


The [[pectoral girdle]] featured a long bar,<ref name=Brown1993/><ref name=Carpenter1999/> not present in juveniles. The [[scapula]] had margins of approximately equal length for the joint with the [[coracoid]] and the articular surface for the upper arm.<ref name=Sachs2005/> The [[anatomical terms of location|anterior]] edge of the pelvic girdle was made up of three almost straight edges directed to the front and sides of the animal. The [[ischium|ischia]], a pair of bones that formed the posterior part of the pelvis, were joined along their medial surfaces.<ref name=Sachs2005/> The limbs of ''Elasmosaurus'', like those of other plesiosaurs, were modified into approximately equally sized rigid paddles.<ref name="Everhart135">Everhart p. 135</ref>
The [[pectoral girdle]] featured a long bar,<ref name=Brown1993/><ref name=Carpenter1999/> not present in juveniles. The [[scapula]] had margins of approximately equal length for the joint with the [[coracoid]] and the articular surface for the upper arm.<ref name=Sachs2005/> The [[anatomical terms of location|anterior]] edge of the pelvic girdle was made up of three almost straight edges directed to the front and sides of the animal. The [[ischium|ischia]], a pair of bones that formed the posterior part of the pelvis, were joined along their medial surfaces.<ref name=Sachs2005/> The limbs of ''Elasmosaurus'', like those of other plesiosaurs, were modified into approximately equally sized rigid paddles.<ref name="Everhart135">Everhart p. 135</ref>

Revision as of 19:47, 18 July 2017

For the album by Matt Costa, see The Elasmosaurus EP.

Elasmosaurus
Temporal range: Late Cretaceous, 80.5 Ma
↓
Reconstructed skeleton in the Rocky Mountain Dinosaur Resource Center
Scientific classification Edit this classification
Domain: Eukaryota
Kingdom: Animalia
Phylum: Chordata
Class: Reptilia
Superorder: †Sauropterygia
Order: †Plesiosauria
Family: †Elasmosauridae
Genus: †Elasmosaurus
Cope, 1868
Species:
†E. platyurus
Binomial name
†Elasmosaurus platyurus
Cope, 1868

Elasmosaurus (/ɪˌlæzməˈsɔːrəs, -moʊ-/;[1] from Greek ελασμος elasmos 'thin plate' (referring to thin plates in its pelvic girdle) + σαυρος sauros 'lizard') is a genus of plesiosaur with an extremely long neck that lived in the Late Cretaceous period (Campanian stage), 80.5 million years ago.[2]

Description

Restoration with size comparison

At 10.3 metres (34 ft) in length,[3] Elasmosaurus was among the largest plesiosaurs. It differs from all other plesiosaurs by having six teeth per premaxilla (the bones at the tip of the snout) and 72 neck (cervical) vertebrae.[4] Only Albertonectes, with its 75 vertebrate, is known to have had more. The two genera have the highest numbers of cervical vertebrae for vertebrates.[5] The skull was relatively flat, with a number of long pointed teeth. The lower jaws were joined at the tip to a point between the fourth and fifth teeth.[4] The neck vertebrae immediately following the skull were long and low, and had longitudinal lateral crests.[6][7] Like most elasmosaurids, Elasmosaurus had around three pectoral vertebrae. The tail included at least 18 vertebrae.[6][7]

The pectoral girdle featured a long bar,[6][7] not present in juveniles. The scapula had margins of approximately equal length for the joint with the coracoid and the articular surface for the upper arm.[4] The anterior edge of the pelvic girdle was made up of three almost straight edges directed to the front and sides of the animal. The ischia, a pair of bones that formed the posterior part of the pelvis, were joined along their medial surfaces.[4] The limbs of Elasmosaurus, like those of other plesiosaurs, were modified into approximately equally sized rigid paddles.[8]

Reconstructed skull and neck, North American Museum of Ancient Life

Certain aspects of the anatomy of Elasmosaurus were fairly derived among elasmosaurids, and plesiosaurs in general.[4] As noted, Elasmosaurus can be distinguished by its six premaxillary teeth and 71 cervical vertebrae.[4] Primitively, plesiosaurs and most elasmosaurids had five teeth per premaxilla. Some elasmosaurids had more: Terminonatator had nine[9] and Aristonectes had 10 to 13.[10] In addition, most plesiosaurs had fewer than 60 cervical vertebrae.[4] Aside from Elasmosaurus, plesiosaurs that exceeded 60 cervicals include Styxosaurus, Hydralmosaurus, Thalassomedon, and Albertonectes.[11]

Elasmosaurus and Albertonectes are the only known plesiosaurs with more than 70 cervicals. However, Elasmosaurus had roughly the same neck length as Thalassomedon[12] because the latter has proportionally longer vertebrae.[13] The presence of the pectoral bar is also considered an advanced feature.[4] The long, low axis centrum differs from the condition seen in most other plesiosaurs, which have centra that are either shorter in length than height, or about equidimensional.[4] Styxosaurus and Hydralmosaurus also have the condition present in Elasmosaurus.[12][14] Another unusual feature of Elasmosaurus is the relatively equal lengths of the margins of the scapula, as mentioned above. Most plesiosaurs had longer margins for articulation with the coracoid than for articulation with the upper arm.[14]

History of discovery

1869 "head-on-the-wrong-end" reconstruction; Cope did not include the "hind" (actually front) paddles in this figure in part due to his erroneous belief that Elasmosaurus was propelled by its extremely long “tail” (neck)

Elasmosaurus platyurus was described in March, 1868 by Edward Drinker Cope[15] from a fossil discovered and collected by Dr. Theophilus Turner, a military doctor, in western Kansas, United States. Although other specimens of elasmosaurs have been found in various locations in North America, Carpenter (1999) determined that Elasmosaurus platyurus was the only representative of the genus.[7]

Outdated restoration of Dryptosaurus confronting two Elasmosaurus, with Hadrosaurus in the background. By Cope, 1869.

When E. D. Cope received the specimen in early March, 1868, he had a pre-conceived idea of what it should look like, and mistakenly placed the head on the wrong end (i.e. the tail). In his defense, at the time he was an expert on lizards, which have a short neck and a long tail, and no one had ever seen a plesiosaur the size of Elasmosaurus. Although popular legend notes that it was Othniel Charles Marsh who pointed out the error, there is no factual justification for this account (see below). However, this event is often cited as one of the causes of their long-lasting and acrimonious rivalry, known as the Bone Wars. In fact, although Marsh personally collected at least one plesiosaur from Kansas, and had several more from Kansas in the Yale Peabody collection, he never published a single paper on them.[16] Other elasmosaurus fossils have been discovered in Montana and Alaska's Talkeetna Mountains, north of Anchorage.[17]

Although Cope verbally announced the discovery of Elasmosaurus platyurus in March 1868, he did not publish the "preprint" of his erroneous reconstruction of Elasmosaurus until August 1869.[18] While much smaller, long-necked plesiosaurs from the Jurassic of England were well known at the time, this was the first time anyone had ever seen a Cretaceous elasmosaur. Cope's reconstruction showed it to have a long sinuous tail like a lizard or a mosasaur. Note that while O.C. Marsh claimed to have pointed out Cope's error "20 years after the fact" in an 1890 newspaper article, it was actually Joseph Leidy who pointed out the problem in his Remarks on Elasmosaurus platyurus address at the Academy of Natural Sciences of Philadelphia meeting on March 8, 1870.

Classification

While numerous species of Elasmosaurus have been named since its discovery, a 1999 review by Ken Carpenter showed that only one, the type species Elasmosaurus platyurus, could be considered valid. Various other species assigned to the genus are either dubious or have been classified in other genera. For example, E. serpentinus has been reclassified as Hydralmosaurus, E. morgani as Libonectes, and E. snowii as Styxosaurus.[7]

By the early part of the Late Cretaceous, these were two distinct groups of plesiosaurs left.[19] Elasmosaurus is the type genus for one of these groups, the elasmosaurids which had extremely long necks with relatively short heads, in contrast to the polycotylids which had shorter necks and relatively larger heads. Late Cretaceous elasmosaurids from the Western Interior of North America have few features that separate them and are morphologically primitive.[7] However, as noted above, Elasmosaurus and some others have some derived features. It has been suggested that Elasmosaurus was closely related to Hydralmosaurus and Styxosaurus due to these advanced features.[4]

Reconstructed skeleton, Canadian Museum of Nature

The following cladogram follows an analysis by Benson & Druckenmiller (2014).[20]

Plesiosauroidea

Paleobiology

Restoration of two Elasmosaurus with inaccurate, snake-like necks, by Charles R. Knight, 1897

Like most plesiosaurs, Elasmosaurus was incapable of raising anything more than its head above the water as it is commonly depicted in art and media. The weight of its long neck placed the center of gravity behind the front flippers. Thus Elasmosaurus could only have raised its head and neck above the water if in shallow water, where it could rest its body on the bottom. The weight of the neck, the limited musculature, and the limited movement between the vertebrae would have prevented Elasmosaurus from raising its head and neck very high as well. The head and shoulders of the Elasmosaurus most likely acted as a rudder. If the animal moved the anterior part of the body in a certain direction, it would cause the rest of the body to move in that direction. Thus, Elasmosaurus could not have swum in one direction while moving its head and neck either horizontally or vertically in a different direction.[21]

Modern restoration showing two individuals with straight necks

Nevertheless, one study found that the necks of elasmosaurs were capable of 75–177˚ of ventral movement, 87–155° of dorsal movement, and 94–176° of lateral movement, depending on the amount of tissue between the vertebrae, which likely increased in rigidness towards the back of the neck. "Swan-like" S-shape neck postures which required more than 360° of vertical flexion were not possible. These flexion range would have allowed elasmosaurs to employ a number of hunting methods including "benthic grazing" and ambush. Elasmosaurs may also have been active hunters in the pelagic zone and used their head and necks to stun prey (similar to modern sea snakes and sea turtles) or used side-swip motions to stun or kill prey with their laterally projected teeth (like sawsharks).[22]

It has been proposed that that as elasmosaurs were likely slow swimmers, they stalked schools of fish, concealing themselves below and moved the head slowly slowly up as they approached. The eyes of the animal could have had stereoscopic vision, which would help it find small prey. Hunting from below would also have helped by silhouetting the prey in the sunlight while concealing Elasmosaurus in the dark waters below. Elasmosaurs probably ate small bony fish and marine invertebrates, as their small, non-kinetic skull would have limited the prey they could eat. The teeth were adapted for seizing prey and not tearing, and hence it was swallowed whole.[23]

It swallowed small stones to aid its digestion.[24] Elasmosaurus is believed to have lived mostly in open ocean. The paddles of Elasmosaurus and other plesiosaurs are so rigid and specialized for swimming that they could not have come on land to lay eggs like sea turtles. Thus it most likely gave live birth to its young like sea snakes.[25] While direct evidence of reproduction in Elasmosaurus is not yet known, the contemporaneous plesiosaur Polycotylus is known to have given birth to live young.[26]

Paleoecology

Elasmosaurus fossils have been found in the Campanian-age Upper Cretaceous Pierre Shale of western Kansas. The Pierre Shale represents a period of marine deposition from the Western Interior Seaway, a shallow continental sea that submerged much of central North America during the Cretaceous.[27]

See also

References

  1. ^ "Elasmosaurus". Oxford Dictionaries UK English Dictionary. Oxford University Press. n.d. Retrieved 2016-01-21.
  2. ^ Carpenter, K. 2003. "Vertebrate Biostratigraphy of the Smoky Hill Chalk (Niobrara Formation) and the Sharon Springs Member (Pierre Shale)." High-Resolution Approaches in Stratigraphic Paleontology, 21: 421-437. doi:10.1007/978-1-4020-9053-0
  3. ^ O'Gorman, J.P. (2016). "A Small Body Sized Non-Aristonectine Elasmosaurid (Sauropterygia, Plesiosauria) from the Late Cretaceous of Patagonia with Comments on the Relationships of the Patagonian and Antarctic Elasmosaurids". Ameghiniana. 53 (3): 245–268. doi:10.5710/AMGH.29.11.2015.2928.
  4. ^ a b c d e f g h i j Sachs, S. (2005). "Redescription of Elasmosaurus platyurus, Cope 1868 (Plesiosauria: Elasmosauridae) from the Upper Cretaceous (lower Campanian) of Kansas, U.S.A". Paludicola. 5 (3): 92–106.
  5. ^ Sach, S.; Kear, B. P.; Everhart, M. (2013). "Revised Vertebral Count in the "Longest-Necked Vertebrate" Elasmosaurus platyurus Cope 1868, and Clarification of the Cervical-Dorsal Transition in Plesiosauria". PLoS ONE. 8 (8): e70877. doi:10.1371/journal.pone.0070877.{{cite journal}}: CS1 maint: multiple names: authors list (link) CS1 maint: unflagged free DOI (link)
  6. ^ a b c Brown, D. S. (1993). "A taxonomic reappraisal of the families Elasmosauridae and Cryptoclididae (Reptilia: Plesiosauroidea)". Révue de Paléobiologie. 7: 9–16.
  7. ^ a b c d e f Carpenter, K. (1999). "Revision of North American elasmosaurs from the Cretaceous of the western interior". Paludicola. 2 (2): 148–173.
  8. ^ Everhart p. 135
  9. ^ Sato, T. (2003). "Terminonatator ponteixensis, a new elasmosaur (Reptilia:Sauropterygia) from the Upper Cretaceous of Saskatchewan"". Journal of Vertebrate Paleontology. 23 (1): 89–103.
  10. ^ Gasparini, Z., Bardet, N., Martin, J.E. and Fernandez, M.S. (2003). "The elasmosaurid plesiosaur Aristonectes Cabreta from the Latest Cretaceous of South America and Antarctica". Journal of Vertebrate Paleontology. 23 (1): 104–115. doi:10.1671/0272-4634(2003)23[104:TEPACF]2.0.CO;2.{{cite journal}}: CS1 maint: multiple names: authors list (link)
  11. ^ Kubo, T.; Mitchell, M. T.; Henderson, D. M. (2012). "Albertonectes vanderveldei, a new elasmosaur (Reptilia, Sauropterygia) from the Upper Cretaceous of Alberta". Journal of Vertebrate Paleontology. 32 (3): 557–572. doi:10.1080/02724634.2012.658124.
  12. ^ a b Welles, S. P. (1943). "Elasmosaurid plesiosaurs with descriptions of new material from California and Colorado". Memoirs of the University of California. 13: 125–254..
  13. ^ Everhart p. 130
  14. ^ a b Sachs, S. (2004). "Redescription of Woolungasaurus glendowerensis (Plesiosauria: Elasmosauridae) from the Lower Cretaceous of Northeast Queensland". Memoirs of the Quennsland Museum. 49: 215–233.
  15. ^ Cope, E. D. (1868). "Remarks on a new enaliosaurian, Elasmosaurus platyurus". Proceedings of the Academy of Natural Sciences of Philadelphia. 20: 92–93.
  16. ^ Everhart pp. 122–123
  17. ^ Newly discovered 'Loch Ness Monster; fossil gets life-size diorama in Anchorage, Alaska Dispatch News, July 25, 2015, Mike Dunham. Retrieved 26 July 2015.
  18. ^ Cope, E. D. 1869. "Synopsis of the Extinct Batrachia and Reptilia of North America, Part I". Transactions American Philadelphia Society New Series, 14:1-235, 51 figs., 11 pls. (pre-print dated August, 1869)
  19. ^ Everhart, p. 129
  20. ^ Benson, R. B. J.; Druckenmiller, P. S. (2013). "Faunal turnover of marine tetrapods during the Jurassic-Cretaceous transition". Biological Reviews. 89: 1–23. doi:10.1111/brv.12038. PMID 23581455.
  21. ^ Everhart, pp. 132-133
  22. ^ Zammit M., Daniels, C. B. and Kear, B. P. (2008). "Elasmosaur (Reptilia: Sauropterygia) neck flexibility: Implications for feeding strategies". Comparative Biochemistry and Physiology - Part A: Molecular & Integrative Physiology. 150 (2): 124–130. doi:10.1016/j.cbpa.2007.09.004. PMID 17933571.{{cite journal}}: CS1 maint: multiple names: authors list (link)
  23. ^ Everhart 133–135
  24. ^ Everhart, pp. 136-137
  25. ^ Everhart, pp. 140
  26. ^ O'Keefe, F. R. and Chiappe, L. M. (2011). "Viviparity and K-selected life history in a Mesozoic marine plesiosaur (Reptilia, Sauropterygia)". Science. 333 (6044): 870–873. doi:10.1126/science.1205689.{{cite journal}}: CS1 maint: multiple names: authors list (link)
  27. ^ Everhart, p. 6

General sources

  • Everhart, M. J. (2005). Oceans of Kansas - A Natural History of the Western Interior Sea. Indiana University. ISBN 0-253-34547-2.

External links

Retrieved from "https://en.wikipedia.org/w/index.php?title=Elasmosaurus&oldid=791202763"