This section is taken from the Dinosaur Field Guide.
Elasmosaurus, like many plesiosaurs, had a small head at the end of a long neck and a mouth full of needle-like teeth. It could swim into schools of fish, moving its head back and forth to catch them. At up to 40 feet (12 m) long, Elasmosaurus was among the largest of the long-necked plesiosaurs.
So far, Elasmosaurus hasn't appeared in any of the films or the novels although a skull of a plesiosaur is in Jurassic Park: The Game and it possibly belongs to Elasmosaurus possibly proving it is in the film canon.
Elasmosaurus is number 119 of the Carnivore Threes that can be created in Jurassic Park III: Park Builder.
In Jurassic Park: Builder, Elasmosaurus can be created in the Aquatic section as a limited edition crustaceavore, even though in reality, it was a piscivore.