Elasmosaurus was a prehistoric sea creature that lived during the late Cretaceous period, roughly 80 million years ago. It was a large marine reptile, measuring up to 45 feet in length, and was one of the largest known plesiosaurs
Elasmosaurus 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 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 now lost pectoral and pelvic girdles, 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.