“This animal spared my life,” says Mexican marine biologist Mauricio Hoyos, who was bitten on the head by a giant Galapagos shark — and lived to tell the story.

With over 30 years of experience studying sharks, Hoyos was diving off the coast of Costa Rica when the 3-meter female attacked as he tried to tag her for research.The bite tore his mask and air hose, leaving him bleeding and nearly out of oxygen, but he managed to reach the surface and survive.Within weeks,…