Some 252 million years ago, the largest extinction event occurred at the end of the Permian age. It wiped out almost 90 percent of all life in water. So far researchers had assumed that the ecosystems gradually recovered from this catastrophe over a long stretch of eight to nine million years and that large predators at the uppermost end of the food chain were the last to reappear. Palaeontologists now show that the food nets during the Early Triassic did not recover in stages. Large predators like, for instance, crocodile-like amphibians and later the precursors of the known plesiosaurs and ichthyosaurs went in search of prey in the oceans soon after the end of the mass extinction. 

Source: Amphibians and dinosaurs were the new large predators after the mass extinction