For the organisms that experience them, cataclysmic events bring death and devastation, but mass extinctions have their positive side, too. Indeed, if it wasn't for mass extinction, we would not be here. Mass extinctions wipe the biological slate clean and leave the door open to organisms that have been kept in the shade. If we travel back in time, the Permian-Triassic mass extinction created an opportunity for the dinosaurs to rise to dominance, following the demise of the large synapsids, i.e., Edaphosaurus, Dimetrodon, and so on. This is known as the Triassic takeover, and as the dinosaurs diversified and grew larger, the surviving synapsids were forced into the shadows as nocturnal, insectivorous animals, and they gradually evolved the characteristics that we know as mammalian. For 160 million years, these animals and their true mammal descendents lived in the shadows of the dinosaurs, scurrying around the feet of the reptilian giants. Then, 65 million years ago, the K-T event ended the dominance of these reptiles and the door was wide open. For a short while after the disappearance of the dinosaurs, the mammals, birds, and crocodiles all vied with each other to take the place of the extinct reptiles. Eventually, the mammals were successful, and they evolved remarkably quickly to fill the niches in the post dinosaur world.
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