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Temporal range: Late Triassic – Late Cretaceous
Elasmosaurus sp by ashere-d5i4md1.jpg
Elasmosaurus platyurus
Scientific classification
Kingdom: Animalia
Phylum: Chordata
Class: Reptilia
Superorder: Sauropterygia
Order: Plesiosauria
Family: Elasmosauridae
Cope, 1869
Referred species
  • Cimoliasauridae Persson, 1960

Elasmosauridae was a family of plesiosaurs, with notably long necks. They had the longest necks of all plesiosaurs and survived from the Early Jurassic to the Late Cretaceous. Their diet consisted of fish and shelless cephalopods. They reached from three meters to fourteen meters in total body length. Their necks alone were usually a little over half the total body length of the animal.