Dinosaurs were present on earth around 230 million years ago in the late Triassic period. They were vertebrate animals and were not the ancestors of Humans. They became extinct in the Cretaceous–Tertiary extinction event. During this period there were extreme changes in weather and climate and Dinosaurs despite being huge animals could not survive these changes and started dying. And eventually became extinct. For complete details see the link below:
en.wikipedia.org