Turtles are reptiles of the order Testudines or Chelonii and are characterised by a special bony shell which is developed from their ribs and acts as a shield against predators.
The turtle order, Testudines or Chelonia, splits into two suborders, Cryptodira and Pleurodira, and then further splits into 13 families, 75 genera and 327 species.
Turtles are residents of every continent except Antarctica and of all the world’s temperate and tropical oceans.
Turtles are a very old group of reptiles, going back about 220 million years. They are one of the oldest reptile groups, more ancient group than snakes or crocodilians.
The lifespan of a turtle varies greatly depending on the species of turtle. For example, a typical pet turtle can live between 10-80 years or so while larger species can easily live over 100 years. Adwaita, an Aldabra giant tortoise that died in 2006 in the Alipore Zoological Gardens of Kolkata, India, is believed to have lived to the age of 255 years.
The largest turtle is the leatherback sea turtle (Dermochelys coriacea). Mature leatherbacks reach about 1.2 to 1.9 meters (3.9-6.2 feet) and 200 to 506 kilograms (441 to 1,116 pounds). The largest leatherback recorded weighed 916 kilograms (2,019 pounds).
The Galapagos Islands are home to the largest terrestrial species, Galapagos tortoise (Chelonoidis nigra). It can grow to over 130 centimeters (51 inches) in length, and weigh about 300 kilograms (660 pounds).
The smallest turtle is the speckled tortoise (Homopus signatus) of South Africa. It measures no more than 8 centimeters (3.1 inches) in length and weighs about 140 grams (4.9 ounces).
Of all the animals with backbones, turtles are the only ones that also have a shell, made up of 59 to 61 bones covered by plates called scutes, which are made of keratin like our fingernails. The shell’s top is called the carapace, and the bottom is the plastron.
The skin of a turtle especially the land tortoises, may look leathery and tough, but it is actually very sensitive.
Turtles are cold-blooded reptiles – their internal temperature varies according to the ambient environment.
Turtles have good eyesight and an excellent sense of smell.
Turtles are thought to have exceptional night vision due to the unusually large number of rod cells in their retinas. Turtles have color vision with a wealth of cone subtypes with sensitivities ranging from the near ultraviolet (UVA) to red.
Turtles don’t have any “outer ear,” the part that sticks out from your head, but they have all the “inner ear”. They have thin flaps of skin covering internal ear bones. The skin flaps allow vibrations and low-frequency sounds in the ear canal — so the turtles can hear to some extent, but their hearing isn’t sensitive.
Turtles do not have teeth, instead they possess a sharp beak that enables them to tear their food.
What turtles eat depends greatly on the type of turtle and its natural habitat. Some turtles are carnivores, while others follow a strictly vegetarian diet. Most turtles, however, are omnivores, eating both animals and plants.
All turtles lay eggs, which they bury in soil, sand, or vegetation. Some species lay only a few oblong-shaped eggs, while others lay dozens to 100 or more round eggs.
For many species, the temperature in the nest determines the gender of the baby turtles: warmer nests result in more females, cooler ones result in more males.
Depending on the species, the eggs will typically take 70–120 days to hatch; any babies that hatch are on their own; the mother does not incubate or care for her eggs or for the hatchlings when they emerge.
Turtles are divided into two groups according to how they retract their necks into their shells. The Cryptodira retract their necks backwards while contracting it under their spine, whereas the Pleurodira contract their necks to the side.
The word chelonian is popular among veterinarians, scientists, and conservationists working with these animals as a catch-all name for any member of the superorder Chelonia, which includes all turtles living and extinct, as well as their immediate ancestors.
In February 2011, the Tortoise and Freshwater Turtle Specialist Group published a report about the top 25 species of turtles most likely to become extinct, with a further 40 species at very high risk of becoming extinct. This list excludes sea turtles, however both the leatherback and the Kemp’s ridley would make the top 25 list.
Turtles, particularly small terrestrial and freshwater turtles, are commonly kept as pets. Among the most popular are Russian tortoises, spur-thighed tortoises, and red-eared sliders.
The fastest turtle is the leatherback turtle—one was clocked swimming at 35 kilometers (22 miles) per hour.
Galápagos tortoises travel at about 0.26 kilometers (0.16 miles) per hour.
Sea turtles excrete salt absorbed in sea water from their eyes, which is why they seem to cry.
Some turtles can live for more than a year without food.
Some turtles clean each other. One turtle uses its jaws to pull algae and loose pieces of shell off the other, and then they switch places.
The flesh of turtles, calipash or calipee, was, and still is, considered a delicacy in a number of cultures.
A pair of Russian tortoises went into space. In 1968, the Soviet Union launched Zond 5, a space probe that was the first spacecraft to orbit the moon. It returned safely and the tortoises survived. They had lost about 10% of their body weight, but they remained active and showed no loss of appetite.