Plesiosaurs were at one time the dominant, large aquatic animal on the planet. However, by the end of the Mesozoic era they had disappeared. Furthermore, they may not have left any direct descendant from their lineage. However, in the step-by-step process of creation of the world, the plesiosaurs played an important role in the food chains of their time, and helped prepare the environment for life today. Furthermore, they continue to live in the human imagination. They are used for illustrations in children's books and play a role in fiction and movies. Although extinct many millions of years ago, plesiousaurs have even been used as the explanation for sightings of the "Loch Ness Monster."