|Named By:||J. Leidy in 1851|
|Time Period:||Late Cretaceous, 80.5 Ma|
|Fossil(s):||Partial remains of two species|
|Classification:||| Chordata | Reptilia | Sauropterygia | Plesiosauria ||
Elasmosaurus (from Greek elasmos elasmos 'thin plate' (referring to thin plates in its pelvic girdle) + sauros 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.