Life cycle , South Africa Most species of tortoises lay small clutch sizes, seldom exceeding 20 eggs, and many species have clutch sizes of only 1–2 eggs. Incubation is characteristically long in most species, the average incubation period are between 100 and 160.0 days. Egg-laying typically occurs at night, after which the mother tortoise covers her
clutch with sand, soil, and organic material. The eggs are left unattended, and depending on the species, take from 60 to 120 days to incubate. The size of the egg depends on the size of the mother and can be estimated by examining the width of the
cloacal opening between the
carapace and
plastron. The plastron of a female tortoise often has a noticeable V-shaped notch below the tail which facilitates passing the eggs. Upon completion of the incubation period, a fully formed
hatchling uses an
egg tooth to break out of its shell. It digs to the surface of the nest and begins a life of survival on its own. They are hatched with an embryonic egg sac which serves as a source of nutrition for the first three to seven days until they have the strength and mobility to find food. Juvenile tortoises often require a different balance of nutrients than adults, so they may eat foods which a more mature tortoise would not. For example, the young of a strictly
herbivorous species commonly will consume
worms or insect
larvae for additional protein. The number of concentric rings on the carapace, much like the cross-section of a
tree, can sometimes give a clue to how old the animal is, but, since the growth depends highly on the accessibility of food and water, a tortoise that has access to plenty of
forage (or is regularly fed by its owner) with no seasonal variation will have no noticeable rings. Moreover, some tortoises grow more than one ring per season, and in some others, due to wear, some rings are no longer visible. Tortoises generally have one of the longest lifespans of any animal, and some individuals are known to have lived longer than 150 years. Because of this, they symbolize longevity in some cultures, such as
Chinese culture. The oldest tortoise ever recorded, and one of the oldest individual animals ever recorded, was
Tu'i Malila, which was presented to the
Tongan royal family by the British explorer
James Cook shortly after its birth in 1777. Tu'i Malila remained in the care of the Tongan royal family until its death by natural causes on May 19, 1965, at the age of 188. The
Alipore Zoo in India was the home to
Adwaita, which zoo officials claimed was the oldest living animal until its death on March 23, 2006. Adwaita (also spelled Addwaita) was an
Aldabra giant tortoise brought to India by Lord Wellesley, who handed it over to the Alipur Zoological Gardens in 1875 when the zoo was set up. West Bengal officials said records showed Adwaita was at least 150 years old, but other evidence pointed to 250. Adwaita was said to be the pet of
Robert Clive.
Harriet was a resident at the
Australia Zoo in Queensland from 1987 to her death in 2006; she was believed to have been brought to England by
Charles Darwin aboard the
Beagle and then on to Australia by
John Clements Wickham. Harriet died on June 23, 2006, just shy of her 176th birthday.
Timothy, a female
spur-thighed tortoise, lived to be about 165 years old. For 38 years, she was carried as a
mascot aboard various ships in Britain's
Royal Navy. Then in 1892, at age 53, she retired to the grounds of
Powderham Castle in
Devon. Up to the time of her death in 2004, she was believed to be the United Kingdom's oldest resident.
Jonathan, a
Seychelles giant tortoise living on the island of
St Helena, may be as old as years. DNA analysis of the
genomes of the long-lived tortoises,
Lonesome George, the iconic last member of
Chelonoidis abingdonii, and the
Aldabra giant tortoise Aldabrachelys gigantea led to the detection of lineage-specific variants affecting
DNA repair genes that might contribute to their long lifespan.
Dimorphism Many species of tortoises are
sexually dimorphic, though the differences between males and females vary from species to species. In some species, males have a longer, more protruding neck plate than their female counterparts, while in others, the claws are longer on the females. The male plastron is curved inwards to aid reproduction. The easiest way to determine the sex of a tortoise is to look at the tail. The females, as a general rule, have smaller tails, dropped down, whereas the males have much longer tails which are usually pulled up and to the side of the rear shell.
Brain The brain of a tortoise is extremely small. Red-footed tortoises, from Central and South America, do not have an area in the brain called the
hippocampus, which relates to emotion, learning, memory and spatial navigation. Studies have shown that red-footed tortoises may rely on an area of the brain called the medial cortex for emotional actions, an area that humans use for actions such as decision making. ==Distribution==