Rise of the dinosaurs.
The Triassic period.
The very first dinosaurs lived during the last part of the late Triassic period, This time frame is estimated to be about 225 to 204 million years ago. During this time the climate was not as it is today. Near the seas and rivers, it was warm and damp. But away from the coasts, far inland, it was much drier. The plants then mostly consisted of ferns, cycads and bamboo like plants called horsetails. All of these plants are very interesting to behold and seem to belong in tropical environments, although ferns are found all over the world. Cycads particularly look like stumpy palm trees. Dinosaurs were not alone during this time and they shared this ancient landscape with many other kinds of animals. They include the earliest turtles, crocodiles and pterosaurs. Pterosaurs are the earliest vertebrates known to have evolved powered flight.
The Earth at this time, all the continents and all the land, were fused together. There was one single landmass surrounded by the rest of the worlds ocean. There is no evidence that either of the planets two poles, the north pole and south pole, were glaciated. Which means that at this time in history the arctic and antarctic regions were warm and temperate.
Life in the Triassic period: The oceans had been massively depopulated by the Permian Extinction when as many as 95 percent of extant marine genera were wiped out by high carbon dioxide levels (252.5 million years ago approximately 27 million years before we enter the Triassic period). Fossil fish from the Triassic Period are very uniform, which indicates that few families survived the extinction. The mid- to late Triassic Period shows the first development of modern stony corals and a time of modest reef building activity in the shallower waters of the Tethys near the coasts of Pangaea (This massive single landmass).
Plants and insects did not go through any extensive evolutionary advances during the Triassic. Due to the dry climate, the interior of Pangaea was mostly desert. In higher latitudes, gymnosperms survived and conifer forests began to recover from the Permian Extinction. Mosses and ferns survived in coastal regions. Spiders, scorpions, millipedes and centipedes survived, as well as the newer groups of beetles. The only new insect group of the Triassic was the grasshopper. During the late Triassic period 220 million years ago, the first true mammals appeared. Some scientists believe that mammals evolved from a group of extinct mammal like reptiles. These primitive early mammals were tiny and are thought to have been nocturnal (active at night).
From 204 to 184 million years ago the world started to change. As the continents started to split apart, the climate altered. It rained more and the world became a lot greener. This time period is the early Jurassic period. This is the age when dinosaurs really began to rule the Earth!