The largest sharks ever to have roamed the oceans parked their young in shallow, warm-water nurseries where food was abundant and predators scarce until they could assume their title as kings and queens of the sea.

But as sea levels declined in a cooling world, the brutal mega-predator, Otodus megalodons, may have found fewer and fewer safe-haven coastal zones where its young could safely reach adulthood, researchers reported Wednesday in The Royal Society journal Biology Letters.