The Cretaceous was the last of the geological periods in which dinosaurs lived. The continents were moving farther apart and so different species evolved on each continent, although many, such as T. rex and Tarbosaurus, were still quite similar.
But at the end of Cretaceous times there was a great catastrophe, perhaps caused by a comet smashing into the Earth. This caused climate change, plants to die, and it is likely that dinosaurs ran out of food. With dinosaurs out of the way, a new group of animals developed. These were the mammals and that includes us.
