Plesiosaurs are a group of marine reptiles which lived during the Mesozoic Era. They are commonly mistaken for dinosaurs by the general public. However, they are not dinosaurs. They are commonly sighted cryptids. Many Sea Monsters and Lake Monsters are thought to be plesiosaurs. These include the Loch Ness Monster, Cadborosaurus, Lizzie, the Loch Lomond Monster, Lake Tianchi Monster, Krussie, The Loch Arkaig Monster, the Zuiyo-maru Carcass, The Stronsay Beast, and Loch Quoich Monster.