Giant tortoises originally made their way to islands from the mainland via oceanic dispersal – for example, the Aldabra Atoll and Mascarenes giant tortoises are related to Madagascan tortoises while the Galapagos giant tortoises are related to South American mainland tortoises. Tortoises are aided in such dispersal by their ability to float with their heads up, and to survive up to six months without food or fresh water.
There are many subspecies of giant tortoises that are found on different islands and have different appearances.
Two things in particular stand out about giant tortoises: their size and their longevity.
They are among the world’s longest-living animals, with an average lifespan of 100 years or more.
The oldest living land animal is believed to be Jonathan, a Seychelles giant tortoise, originally from the Seychelles but now a long-time resident of the remote South Atlantic island of St Helena. He is believed to have been born c. 1832, thus making him 187 years old in 2019. His age has been reliably estimated from the fact that he was said to be “fully mature” (and hence at least 50 years old) when he arrived on the island in 1882.
They can be aged by studying growth rings on their shells, which is how we know they are the longest lived vertebrate on record.
Giant tortoises can weigh more than 400 kg (880 lb) and can grow to be more than 1.3 m (4 ft 3 in) long.
Goliath was the biggest tortoise ever weighed. He was 135.8 cm (4 ft 5 in) long, 102 cm (3 ft 4 in) wide and 68.5 cm (2 ft 3 in) high, and he weighed in at 417 kg (919 lb). Probably, there where and are bigger tortoises but how many people have successfully manoeuvred a slow-moving, 400-kg+ creature on to a set of giant scales?
All tortoises are shielded by the protective covering of their shells. The top shell of of a tortoise like from other is called the carapace – the bottom shell that covers a tortoise’s belly is called the plastron.
Giant tortoises live out their lives dozing off in the sun for up to 16 hours a day. They will spend the other portions of their lives munching away on grass, leaves and cactus.
Giant tortoises lay eggs. Females lay their eggs in nest holes, which they cover and leave. Babies hatch in four to eight months. They are on their own from the beginning.
The Galápagos tortoise, from which the name Galapagos derives, have come to symbolize the islands, their unique fauna, and the threats to it.
Remains have been found in the Canary Islands of two extinct species of large tortoises: the Tenerife giant tortoise and the Gran Canaria giant tortoise. These species are believed to have died out due to volcanic eruptions.
Tortoises arrived on the Galápagos Islands about 3 million years ago.
When Spanish navigator Tomás de Bertanga and his fellow explorers discovered the Galápagos Islands in 1535, they found so many giant tortoises there that they named the islands Galápagos, Spanish for “tortoise.” Biologists estimate that 250,000 tortoises inhabited the islands when Bertanga and his men arrived.
Giant tortoises were highly prized by the pirates and whalers who frequented the islands from the 17th through 19th century since they could be kept alive on ships for months, thus providing fresh meat and supplementing what must have been a very dull diet.
Darwin reported that “the breast-plate roasted, with the flesh on it, is very good – and the young tortoises make excellent soup – but otherwise the meat to my taste is indifferent.”
The Galápagos tortoise numbers declined from over 250,000 in the 16th century to a low of around 3,000 in the 1970s. This decline was caused by overexploitation of the species.
Giant tortoises are not known for their speed. However, when in the Galápagos in 1835, Charles Darwin found that they moved faster than he’d imagined.
Charles Darwin took 3 giant tortoises from the Galápagos in 1836. He called Galápagos tortoises “inhabitants of some other planet.”
The closest living relative of the Galapagos giant tortoise is the small Chaco tortoise from South America, although it is not a direct ancestor.
Aldabra is the world’s second-largest coral atoll. Due to difficulties of access and the atoll’s isolation, Aldabra has been protected from human influence and thus retains some 152,000 giant
tortoises, the world’s largest population of this reptile. Aldabra atoll was designated a UNESCO World Heritage Site in 1982.