Late Jurassic period (~156-147 mya)
There were two main body shapes for the plesiosaurs: the long-necked small-headed forms, and the short-necked large-headed forms like Pliosaurus. The pliosaurids were apex predators, feeding on fish, cephalopods, and other marine reptiles, with the largest genera reaching lengths of around 10-13m (~33-43ft). There’s no current evidence for any of them growing significantly bigger than that – the 25m (82ft) Liopleurodon depicted in Walking With Dinosaurs was a complete fabrication.
Color palette used: “Shiny Giratina”