Editing Elasmosaurus (section)

{{short description|Genus of reptiles (fossil)}}
{{Use mdy dates|date=April 2021}}
{{Speciesbox
| fossil_range     = [[Late Cretaceous]] ([[Campanian]]), {{fossilrange|80.64|77}}
| image            = Elasomosaurus Face Clean.png
| image_caption    = Reconstructed skeleton in the [[Rocky Mountain Dinosaur Resource Center]]
| image_alt        = Photo of a mounted skeleton on a transparent background
| genus            = Elasmosaurus
| display_parents  = 2
| species          = platyurus
| parent_authority = [[Edward Drinker Cope|Cope]], 1868
| authority        = Cope, 1868
| synonyms = * ''[[Discosaurus]] carinatus'' <small>Cope, 1868</small>
}}

'''''Elasmosaurus''''' ({{IPAc-en|ɪ|ˌ|l|æ|z|m|ə|ˈ|s|ɔːr|ə|s|,_|-|m|oʊ|-}}{{refn|{{Cite dictionary |url=http://www.lexico.com/definition/Elasmosaurus |archive-url=https://web.archive.org/web/20200728103919/https://www.lexico.com/definition/elasmosaur?s=t |url-status=dead |archive-date=2020-07-28 |title=Elasmosaurus |dictionary=[[Lexico]] UK English Dictionary |publisher=[[Oxford University Press]]}} }}) is a [[genus]] of [[plesiosaur]] that lived in North America during the [[Campanian]] stage of the [[Late Cretaceous]] period, at about 80.6 to 77{{nbsp}}million years ago. The first specimen was discovered in 1867 near [[Fort Wallace]], Kansas, US, and was sent to the American paleontologist [[Edward Drinker Cope]], who named it '''''E.{{nbsp}}platyurus''''' in 1868. The [[Generic name (biology)|generic name]] means "thin-plate reptile", and the [[specific name (zoology)|specific name]] means "flat-tailed". Cope originally reconstructed the skeleton of ''Elasmosaurus'' with the skull at the end of the tail, an error which was made light of by the paleontologist [[Othniel Charles Marsh]], and became part of their "[[Bone Wars]]" rivalry. Only one incomplete ''Elasmosaurus'' skeleton is definitely known, consisting of a fragmentary skull, the spine, and now lost [[pectoral girdle|pectoral]] and [[pelvic girdle]]s, and a single species is recognized today; other species are now considered invalid or have been moved to other genera. A fragmentary specimen from Germany may belong to this genus.

Measuring {{convert|10.3|m|sp=us}} in length, ''Elasmosaurus'' would have had a streamlined body with paddle-like limbs, a short tail, a small head, and an extremely long neck. The neck alone was around {{convert|7.1|m|sp=us}} long. Along with its relative ''[[Albertonectes]]'', it was one of the longest-necked animals to have lived, with the second largest number of neck [[vertebrae]] known, 72, 4 fewer than ''Albertonectes''. The skull would have been slender and triangular, with large, fang-like teeth at the front, and smaller teeth towards the back. It had six teeth in each [[premaxilla]] of the upper jaw, and may have had 14 teeth in the [[maxilla]] and 19 in the [[dentary]] of the lower jaw. Most of the neck vertebrae were compressed sideways, and bore a longitudinal crest or keel along the sides.

The family [[Elasmosauridae]] was based on the genus ''Elasmosaurus'', the first recognized member of this group of long-necked plesiosaurs. Elasmosaurids were well adapted for aquatic life, and used their flippers for swimming. Contrary to earlier depictions, their necks were not very flexible, and could not be held high above the water surface. It is unknown what their long necks were used for, but they may have had a function in feeding. Elasmosaurids probably ate small fish and marine [[invertebrates]], seizing them with their long teeth, and may have used [[gastroliths]] (stomach stones) to help digest their food. ''Elasmosaurus'' is known from the [[Pierre Shale]] formation, which represents marine deposits from the [[Western Interior Seaway]].