There have actually been more than 100 species of creatures on Earth before the dinosaurs. The time when dinosaurs roamed the earth it came after the order decided to annihilate the species that was currently in charge of planet Earth. They had become too ambitious and had plans to use Earth’s resources in a way that would completely destroy everything and create a world that was completely void of nature.
This was the moment when the order wiped out that species and decide to populate the planet with creatures that had no intelligence for anything but basic survival. Then the humans took the place of intelligent creatures, but so far they seem to be headed to the same fate of the last species that got eradicated. Hopefully the human race will start to evolve faster into a species that is worth keeping on Earth for much longer.