Elasmosaurus is a member of a group of extinct reptiles known as the plesiosaurs. Known for its extremley long neck, its neck alone had more than 70 vertebrae. It had a rather small head in comparison to its body. It weighed around 2.2 tons, and was 14m (46 ft) long, making it longer than most modern day sharks, and making it the second longest plesiosaur ever.

Its small head and sharp, pointed teeth may indicate that this creature most likely ate very small fish, squid, or ammonite, perhaps prying out the soft bodies of the mollusks out of their hard shells with their small, slim heads, and using their sharp, pointed teeth like meat hooks. Elasmosaurs probably hunted using stealth, as they were rather slow reptiles unlike animals like the icthyosaurs. They were probably hunted by animals like pliosaurs, mosasaurs or prehistoric sharks.

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