Long-necked plesiosaurs were marine reptiles that lived during the Mesozoic Era, particularly in the Jurassic and Cretaceous periods. They are known for their distinctive long necks, which could have had up to 76 vertebrae, allowing them to reach and catch fish and other prey in the water. Plesiosaurs had a broad body, four flippers, and a small head, making them well-adapted for swimming. These creatures were not dinosaurs but belonged to a separate group of reptiles. Fossils of long-necked plesiosaurs have been found in various locations around the world, providing valuable insights into their size, diet, and habitat. Their unique body structure has fascinated paleontologists and the public alike.