The first dinosaurs evolved during the middle to late Triassic period—about 230 million years ago—in the part of the supercontinent of Pangea that now corresponds with South America. Before then, the dominant land reptiles were archosaurs (ruling lizards), therapsids (mammal-like reptiles), and pelycosaurs (typified by Dimetrodon). For 20 million or so years after dinosaurs evolved, the most fearsome reptiles on Earth were prehistoric crocodiles. It was only at the beginning of the Jurassic period, 200 million years ago, that dinosaurs truly began their rise to dominance.

With our 100-year-max life spans, humans aren't well adapted to understanding "deep time," as geologists call it. To put things in perspective: Modern humans have only existed for a few hundred thousand years, and human civilization only got started about 10,000 years ago, mere blinks of the eye by Jurassic time scales. Everyone talks about how dramatically (and irrevocably) the dinosaurs went extinct, but judging by the whopping 165 million years they managed to survive, they may have been the most successful vertebrate animals ever to colonize Earth.