It is interesting to note that at the beginning of the Mesozoic, there were no true dinosaurs; other reptiles dominated the landscape. But by the end of the Triassic period, the dinosaurs became dominant, and they stayed that way for around 160 million years. Dinosaurs were not the only form of life that existed during this time. For example, there were smaller, lizard-like reptiles, small early mammals, insects, amphibians, invertebrates, and a wide variety of plants. In fact, these organisms helped the dinosaurs to stay in charge because many of the dinosaurs used this abundance of life for their sustenance and growth.