Elasmosaurus was a large species of plesiosaur that lived during the Late Cretaceous period of North America. In that time, North America was split by a large open sea, called the Western Interior Seaway, in which many marine reptiles lived. The neck of Elasmosaurus was very long; possible the longest neck in the animal kingdom, consisting of 72 vertebrae! As falsely depicted on many paintings and illustrations, Elasmosaurus wasn’t capable of lifting its head far above the water level. Most likely, Elasmosaurus used its neck for hunting fish around rocky reefs or for lunging at large schools of fish.
The genus of Elasmosaurus only exists of a single species. Many species have been put within this genus but all were placed under other genuses of plesiosaurs. Fossils of E. platyurus were found in 1867 during the construction of a railway in Kansas (USA). When Cope tried to depict the specimen, he put the skull on the wrong end of the body, which made the specimen having a short neck and a very long tail. This mistake was probably made due to the fact that the skull was found near the tail instead of the neck vertebrae.
Sachs, S. (2005). Redescription of Elasmosaurus platyurus Cope 1868 (Plesiosauria: Elasmosauridae) from the Upper Cretaceous (lower Campanian) of Kansas, USA. Paludicola, 5(3), 92-106.