Come with me and take a journey through the Cretaceous! The Cretaceous period began 145 million years ago after the end of the Jurassic period and ended 66 million years ago. The Cretaceous period was the third and final period of the Mesozoic era. This was the age of the Dinosaurs. It was in the Cretaceous that saw the rise of Tyrannosaurus rex and Triceratops. In the sky, you would meet Quetzalcoatlus, the largest pterosaur that ever lived, with a wingspan the size of a small plane. In the seas, you would find mosasaurs and plesiosaurs. it was in the Late Cretaceous that saw the first of placental mammals. One of the current theories is that an asteroid impacted the Earth 66 million years ago and ushered in the end of the dinosaurs and with them the Cretaceous period.