Giant Galapagos Tortoise gulps water at his favorite drinking hole
The Galapagos Tortoises are famous for being enormous animals. Weighing as much as 225kg (500lbs) when full grown, they could completely fill the passenger compartment of a small car. They are so slow moving that we would expect them to be easy prey for almost any creature. But the truth is much more complex. They have evolved in a way that provides them with an ingenious defense against being eaten. They cannot outrun any other creatures. They don't have teeth or claws that could be used as weapons. They have almost no ability to fight. But what they do have is the ability to use time and outwait any other creature on earth.
The giant tortoises eat and drink in quantities that allow them to go without food and water for over a year. Their shells are an impenetrable armor, and their leathery arms and legs are also like armor. They retract their head into their shells, pull their limbs in tight against their bodies and rest their incredible weight flat on the ground. Most predators would realize after a few minutes, or possibly hours, that there is nothing they can do to eat such a well defended animal as the tortoise. Once they have become large enough that they cannot be flipped over easily, the giant tortoise merely has to remain in this position until the threat goes away.
Galapagos Tortoises could wait until a predator actually dies of starvation, or becomes threatened by another, larger predator, having to abandon its attempt to eat the tortoise. This thirsty giant demonstrates how much water they can take in at once as he gulps for several minutes without stopping. His throat moves rhythmically as the water is swallowed. It is obvious that this much water would last a tortoise for a long time. Tortoise have a tough, scaly skin that prevents water loss through evaporation. They can also limit their urine production in times of drought, further lessening their need to drink.
The Giant Tortoises of the Galapagos are descended from the African Giant Tortoises, believed to have made their way to these islands accidentally on large rafts of drifting vegetation. Few species would survive such a long journey without food and water, but the giant tortoises were able to do just that. They have adapted well to life on the Galapagos Islands and have even overcome the troubles created by long droughts and lack of green vegetation. Needing to reach the higher leaves, the tortoises with deeper indentations on their carapace (upper shell) were able to stretch their long necks higher. Survival of specific tortoises led to evolution of this trait and they became the Galapagos Tortoises that we know today. They all have different shell shapes, depending on which island they are from, but they all differ greatly from their ancestors on the African continent.