Elasmosauridae was the family of plesiosaurs. They had the longest necks of the plesiosaurs and survived from the Early Jurassic to the end of the Cretaceous. They had a diet of fish and shelless cephalopods.
The earliest elasmosaurids were small, about 3 m. At the end of the Cretaceous, elasmosaurids grew as large as 14 m., such as Elasmosaurus. Their necks were the longest of all the plesiosaurs, with anywhere between 32 to 71 cervical vertebrae They weighed up to several tons.