Dinosaurs are a diverse group of reptiles of the clade Dinosauria. They first appeared during the Triassic period, between 243 and 233.23 million years ago, although the exact origin and timing of the evolution of dinosaurs is the subject of active research.
All continents during the Triassic Period were part of a single land mass called Pangaea. This meant that differences between animals or plants found in different areas were minor.
The climate was relatively hot and dry, and much of the land was covered with large deserts. Unlike today, there were no polar ice caps.
It was in this environment that the reptiles known as dinosaurs first evolved. Reptiles tend to flourish in hot climates because their skin is less porous than, for example, mammal skin, so it loses less water in the heat. Reptile kidneys are also better at conserving water.
Toward the end of the Triassic, a series of earthquakes and massive volcanic eruptions caused Pangaea to slowly begin to break into two. This was the birth of the North Atlantic Ocean.
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