Tortoise

This article is about the reptile. For other uses, see Tortoise (disambiguation).

Tortoises are reptiles in the family Testudinidae, part of the group Testudines. The name of the group comes from the Latin word for "tortoise." Like other turtles and their relatives, tortoises have a shell that protects them from predation and other dangers. Their shells are usually hard. Like other members of the suborder Cryptodira, they pull their necks and heads straight back into the shell to keep them safe.

Tortoises come in many sizes. Some, such as the Galápagos giant tortoise, grow to more than 1.2 metres (3.9 feet) long. Others, like the speckled Cape tortoise, have shells that are only 6.8 centimetres (2.7 inches) long. Some of the largest kinds, including the Galápagos giant tortoise and the Aldabra giant tortoise, can weigh over 100 kilograms (220 pounds). Tortoises are usually active during the day. They may be more active at dawn and dusk, depending on the temperature. They are generally shy animals that like to keep to themselves.

Tortoises are some of the longest-living land animals in the world, though scientists do not agree on which species lives the longest. Galápagos tortoises are known to live over 150 years. An Aldabra giant tortoise named Adwaita may have lived about 255 years. Most tortoise species can live 80 to 150 years.

Tortoises are usually slow-moving, calm, and gentle.

Terminology

The words turtle, tortoise, and terrapin are used in different ways depending on where people speak English. People do not always use them the same way. These are common names, not exact scientific labels.

The American Society of Ichthyologists and Herpetologists uses "turtle" for all members of the group Testudines. It uses "tortoise" for turtles that move slowly on land. In America, "terrapin" can mean small turtles that live in fresh or salty water, such as the diamondback terrapin. Some land turtles in the genus Terrapene are called box turtles instead of tortoises. In Britain and in International English, "tortoise" is used for all turtles that live on land. "Terrapin" refers to a larger group of turtles that spend much of their time in water. In Australia, freshwater turtles have long been called "tortoises." Some experts prefer the name "freshwater turtle" to avoid confusion.

Biology

Most tortoise species lay small clutch sizes. They usually lay no more than 20 eggs, and many lay only 1 or 2. Eggs are often laid at night. The mother covers them with sand, soil, and plant material. In most species, the eggs take a long time to develop, usually between 100 and 160 days. During this time, they are left alone. The size of an egg depends on the size of the mother. It can be estimated from the width of the cloacal opening between the carapace and plastron. Females often have a V-shaped notch below the tail that helps the eggs pass. When a baby is fully formed, it uses an egg tooth to break out of its shell. Then it digs up to the surface of the nest and survives on its own. For its first three to seven days, it gets food from a small egg sac. Young tortoises often need different nutrients than adults. A young herbivorous species may eat worms or insect larvae to get extra protein. The rings on the carapace are a bit like the rings in a tree. They can sometimes show how old an animal is. Growth depends on food and water. A tortoise with plenty of forage and no seasonal changes may have no visible rings. Tortoises generally live longer than almost any other animal, and some have lived more than 150 years. Because of this, they are a symbol of long life in some cultures, such as Chinese culture.

The oldest tortoise ever recorded was Tu'i Malila. The British explorer James Cook gave it to the Tongan royal family shortly after it was born in 1777. It lived until it died of natural causes on May 19, 1965, at the age of 188. The Alipore Zoo in India was home to Adwaita, an Aldabra giant tortoise. Zoo officials claimed it was the oldest living animal until it died on March 23, 2006. Records suggested it was at least 150 years old, while other evidence pointed to 250. Harriet lived at the Australia Zoo in Queensland from 1987 until her death in 2006. She is believed to have been brought to England by Charles Darwin aboard the Beagle. Timothy, a female spur-thighed tortoise, lived to be about 165 years old. She was a mascot on ships in the Royal Navy for 38 years. Then she retired to the grounds of Powderham Castle in Devon. Scientists studied the genomes of Lonesome George, the last member of Chelonoidis abingdonii, and an Aldabra giant tortoise. They found changes in DNA repair genes that might help explain why these animals live so long. Many tortoise species are sexually dimorphic, which means males and females look different. The differences vary by species. The easiest way to tell a tortoise's sex is to look at its tail. Females usually have shorter tails that droop down. Males have longer tails that are held up to the side. A tortoise's brain is extremely small. Red-footed tortoises, from Central and South America, do not have a hippocampus. This part of the brain relates to emotion, learning, memory, and finding your way around.

Distribution

Tortoises live in many parts of the world. They are found from southern North America to southern South America, around the Mediterranean Sea, across Eurasia to Southeast Asia, in sub-Saharan Africa, on Madagascar, and on some Pacific islands. They are not found in Australasia. Tortoises live in many kinds of places, such as deserts, dry grasslands, scrub, and wet evergreen forests. They live from sea level up to the mountains. Most kinds live in dry, semiarid places.

Long ago, many large islands had giant tortoises. Tortoises are good at oceanic dispersal, which means they can travel across the ocean. They cannot swim, but they can go for months without food or fresh water. Because of this, some have traveled more than 740 km while floating at sea. On islands with few predators or competitors, giant tortoises grew very large. In many places, they became the main large herbivores, which are animals that eat plants.

Today, only two kinds of giant tortoise are still alive. One is the Aldabra giant tortoise, which lives on Aldabra Atoll. The other is the Galapagos giant tortoise, which has about a dozen subspecies on the Galapagos Islands. Until recently, giant tortoises lived on almost every major group of islands. These included the Bahamas, the Greater Antilles (including Cuba and Hispaniola), the Lesser Antilles, the Canary Islands, Malta, the Seychelles, the Mascarene Islands (including Mauritius and Reunion), and Madagascar. Most of these tortoises disappeared after people arrived on the islands. Many giant tortoises belong to different groups, called genera, such as Megalochelys, Chelonoidis, Centrochelys, Aldabrachelys, Cylindraspis, and Hesperotestudo. Scientists think these tortoises became large separately, on their own, through convergent evolution. Giant tortoises are not found in Australasia or on many southern Pacific islands. On those islands, the meiolaniid stem turtles are thought to have filled the same role. These turtles were not closely related to tortoises. Giant tortoises also lived on the mainland of North America, South America, Europe, Asia, and Africa between the Oligocene and Pliocene periods. All of them are now extinct, and human activity is also thought to have played a part in this.

Diet

Tortoises are usually strict herbivores, which means they eat only plants. They eat grasses, weeds, leafy greens, flowers, and some fruits. Sometimes, though, tortoises have been seen hunting and eating birds. Pet tortoises usually need diets based on wild grasses, weeds, leafy greens, and certain flowers. Some species eat worms or insects and dead animals in their natural homes. Too much protein is harmful for plant-eating tortoises. It has been linked to shell problems and other health issues. Different tortoise species have very different food needs.

Behavior

Tortoises talk to each other in a different way from many other reptiles. Their shells and short legs make it hard to move around, so visual communication is not a strong way for them to send messages.

Instead, tortoises use olfactory cues, or smells, to tell whether another tortoise is male or female. This helps them find a possible mate. Tactile communication, or touch, is important when tortoises meet each other. They use ramming, or bumping into each other, to send messages.

Taxonomy

This species list mostly follows the Turtle Taxonomy Working Group (2021) and the Turtle Extinctions Working Group (2015).

Phylogeny

A molecular phylogeny of tortoises, based on Le et al. (2006), is shown below:

A different family tree, based on mtDNA analysis, was found by Kehlmaier et al. (2021):

In 2023, Kehlmaier again found a family tree that looked very similar to the 2021 one. This supported the idea that the extinct Cylindraspis is evolutionarily distinct from the others. However, Gopherus and Manouria swapped positions, so Gopherus became the earliest-branching genus.

In human culture

Further information: Cultural depictions of turtles

See also: World Turtle

In Hinduism, Kurma (Sanskrit: कुर्म) was the second Avatar of Vishnu. Like the Matsya Avatara, Kurma also belongs to the Satya Yuga. Vishnu took the form of a creature that was half-man and half-tortoise. He is usually shown with four arms. After the Great Flood, he rested at the bottom of the ocean. The other gods placed a mountain on his back so they could stir the sea and find ancient treasures of the Vedic peoples.

In Judaism, tortoises are seen as unclean animals. Early Christians also thought of tortoises as unclean. In Chinese and Japanese folk religion, tortoises are seen as oracular animals. Long ago, people in China used tortoise shells as oracle bones to try to predict the future. In Ancient Greek mythology, Hermes made the first lyre from a tortoise. In September 1968, two Russian tortoises became the first animals to fly around the Moon. Their Zond 5 mission brought them safely back to Earth.