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. Apex predators -- large predators at the uppermost end of the food chain -- are extremely important for the health and stability of an ecosystem. They eradicate sick and weak animals and exercise constantselection pressure on the species they prey on.

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