Elasmosaurus platyurus was a large marine reptile from the Late Cretaceous, known for its extremely long neck, which comprised about half its total length. It inhabited the Western Interior Seaway of North America, preying on fish and other small marine organisms. Its streamlined body and paddles enabled efficient swimming.

Elasmosaurus platyurus, a genus of plesiosaur, lived during the Late Cretaceous period. Fossils have primarily been found in the Western Interior Seaway, a large inland sea that divided North America into eastern and western landmasses.

During the Late Cretaceous, the Western Interior Seaway was a warm, shallow sea with a subtropical climate. This environment was rich in marine life, providing ample food sources for Elasmosaurus.

Elasmosaurus platyurus was a marine reptile that likely occupied a niche as a top predator in the Western Interior Seaway. It is believed to have used its long neck to catch fish and other small marine animals, allowing it to hunt with precision in the open ocean.