Plesiosauridae is a family of marine reptiles that lived during the Mesozoic Era, primarily in the Late Jurassic to the Late Cretaceous periods. They are characterized by their long necks, small heads, and large, paddle-like limbs, which made them efficient swimmers. Plesiosaurids are often depicted as having a body shape similar to that of modern sea turtles. These creatures were carnivorous and likely fed on fish and other marine animals. Fossils of plesiosaurids have been found on every continent, indicating their widespread distribution in ancient oceans. Their unique anatomy and adaptations make them a fascinating subject of study in paleontology.