What was the Cretaceous Period?
The Cretaceous period is the third of three periods of the Mesozoic Era, the “middle era” of complex multicellular life on the Earth. The Cretaceous period extended from the end of the Jurassic period, about 145 million years ago, to approximately 65 million years ago, when the Cretaceous–Tertiary extinction event wiped out most of the dinosaurs. The ancestors of modern-day birds are dinosaurs that survived. The Cretaceous period was an extremely important period for life on Earth. The diversity and size of dinosaurs was at its height. Insects began to diversify as well. The maniraptora clade evolved, a transition clade between dinosaurs and birds. Pterosaurs continued to rule the sky, specializing in an ecological niche similar to modern-day birds for over 150 million years. The Cretaceous oceans started off being dominated by plesiosaurs and pliosaurs, as they had for most of the Mesozoic era. But by the mid-Cretaceous period they started to decline, and modern-day sharks, rays, and
