But scientists recently found members of one of those species, the Floreana tortoise, living around a volcano in the Galápagos Islands.
Ironically, the populations were saved, in part, by the human explorers who used to eat them.
Typically, each tortoise species in the Galápagos is native to a specific island and doesn't usually move around to others.
But when mariners showed up, they carried them from island to island.
The tortoises who survived then settled in their new homes.
Scientists recognised the Floreanas by their saddle-shaped shells, which differ from most of the dome-shaped shell species living near the volcano.
And this might just be the tip of the iceberg.
Scientists only looked at a quarter of the land that tortoises occupy around the volcano, so other species thought to be extinct, like relatives of a late Pinta tortoise called Lonesome George, may still be in the same area.