page_title: Elasmosaurus
section_title: Paleobiology
hierarchical_section_title: Elasmosaurus / Paleobiology
caption_attribution_description: English: Elasmosaurus platyurus swimming with straight necks
context_page_description: Elasmosaurus is a genus of plesiosaur that lived in North America during the Campanian stage of the Late Cretaceous period, about 80.5 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. platyurus in 1868. The generic name means "thin-plate reptile", and the 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 the pectoral and pelvic girdles, and a single species is recognized today; other species are now considered invalid or have been moved to other genera.
  Measuring 10.3 meters long, 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 7.1 meters long.
context_section_description: Elasmosaurids were fully adapted to life in the ocean, with streamlined bodies and long paddles that indicate they were active swimmers. The unusual body structure of elasmosaurids would have limited the speed at which they could swim, and their paddles may have moved in a manner similar to the movement of oars rowing, and due to this, could not twist and were thus held rigidly. Plesiosaurs were even believed to have been able to maintain a constant and high body temperature (homeothermy), allowing for sustained swimming.
  A 2015 study concluded that locomotion was mostly done by the fore-flippers while the hind-flippers functioned in maneuverability and stability; a 2017 study concluded that the hind-flippers of plesiosaurs produced 60% more thrust and had 40% more efficiency when moving in harmony with the fore-flippers. The paddles of plesiosaurs were so rigid and specialized for swimming that they could not have come on land to lay eggs like sea turtles. Therefore, they probably gave live-birth (viviparity) to their young like sea snakes. Evidence for live-birth in plesiosaurs is provided by the fossil of an adult Polycotylus with a single fetus inside.
caption: Restoration showing two individuals swimming with straight necks
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