1-2"

Approximately 93 million to 70 million years old

Elasmosaurus was a plesiosaur which is a type of marine reptile. It was not actually a dinosaur as some would assume, though it coexisted with many dinosaurs. Funny enough, The Loch Ness Monster is believed by some to be an Elasmosaurus but you'll see why below that couldn't be the case (and for other fairly obvious reasons).

The first Elasmosaurus fossil was discovered in 1868, shortly after the end of the Civil War. A military doctor in western Kansas discovered a fossil of Elasmosaurus. It was actually named by an American paleontologist Edward Drinker Cope, who received the specimen shortly after its discovery. Kansas may seem like an odd place to find marine fossils, especially of this size but, during the late Cretaceous, the American West was covered by a shallow body of water called the Western Interior Sea. Today, paleontologists spend a good deal of time in the American Mid-West looking for aquatic fossils to help us better understand the earth's ancient past. 

Getting back to the Elasmosaurus, it was truly an impressive animal. It had as many as 76 vertebrae in its neck alone and could reach a length of about 43 feet from snout to tail. It used this long neck to snap up fish and other prey with lightning fast strikes. At such a length, it's believed to have maneuvered its head shockingly fast under water and its long dagger-like teeth made it an expert fisherman. While this comically long neck may have had its advantages under the water, scientists have concluded that it was incapable of raising its head out the water given the enormous size and weight of its neck. It was most likely incapable of holding anything more than its tiny head above the water (so much for the Loch Ness Monster theory...) which would have been necessary as it did need to breathe oxygen. One thing people often forget about Elasmosaurus, and other marine reptiles, is that these creatures had to surface occasionally for air. They weren't equipped with gills, like fish and sharks, and couldn't live constantly submerged beneath the waves. The question then becomes exactly how often Elasmosaurus had to surface for oxygen? We don't know for sure, but given its size and estimated lung size, it isn't out of the realm of possibility for a single gulp of air could fuel them for 10 to 20 minutes.