At the time, the super-sized reptiles were common, but the introduction of wild goats, which ate the vegetation that formed their diet, and the hunting habits of passing sailors -- left them on the brink of extinction.

CNN: Lonesome George, last of the Pinta Island tortoises, dies

Humans have introduced dozens of species into Australia - including wild horses, pigs, goats, dogs, cats, rabbits and foxes - and these have now become a major problem for the ecosystem.

BBC: Australia, home to the world's largest camel herd

GARCIA-NAVARRO: Galapagos is named after these reptiles, but their populations have been hurt in the wild by rats, pigs and goats.

NPR: Common Intruders Threaten Galapagos Species