The Galápagos Giant Tortoise (Geochelone elephantophus, tortuga gigante) is the namesake of the archipelago. The word “galápagos” refers to an old Spanish saddle very similar in shape to the shell of one of two major types of tortoises: saddleback tortoises and dome-shaped tortoises. The saddleback tortoises have long necks, are smaller in stature, and live in low areas with little vegetation. Dome-shaped tortoises live in the highlands of the larger islands. Males have longer tails and are bigger than the females. Within these two categories fall 11 subspecies (once 14) of Galápagos giant tortoise, each having evolved differently due to habitat isolation.
The Galápagos giant tortoise is most well-known for its immense size: it can grow to over 1.5 meters in length and up to 250 kg in weight. No one knows how long they can live, but growth ring approximations on their shells indicate a life span of at least 150 years. The rate of growth is controlled by the availability of food, their food of choice extending to over fifty species of plants, including poison apple, guava, and cactus pads, among others.
Female tortoises reach sexual maturity between 25 and 30 years of age, at which time they will migrate to the lowlands, locate a suitably earthy area, dig a shallow pit, and deposit between two and 16 ping-pong ball-sized eggs. They will cover the eggs with mud and urine and leave the eggs incubating for 120 to 140 days. The distance traveled by female tortoises to lay their eggs is the greatest distance any tortoise will travel in its lifetime; males only move 4-5 km/year and can often stay for days in their mud holes without moving.
The most famous Galápagos giant tortoise is Lonesome George, the last of the Pinto island subspecies and a charismatic (and not very sexually promiscuous) representative of the plight of the tortoises due to human activity. Because tortoise populations have been drastically reduced from predation by introduced species, the Charles Darwin Research Station has spearheaded a very successful captive breeding and reintroduction program.
The easiest places to see Galápagos giant tortoises (both types) are at the Charles Darwin Research Station and in the Santa Cruz highlands.