Turtles belong to the Chelonia or Testudines order of reptiles. They have a bony or cartilaginous shell or carapace that serves as a shield and is formed from their ribs. Extant (alive) and extinct species of testudines are included. Its earliest members were discovered in the Middle Jurassic. They are one of the earliest reptile families, predating snakes and crocodilians.

Turtles are ectotherms, or cold-blooded animals, which means their internal temperature fluctuates depending on their surroundings. Leatherback sea turtles, on the other hand, have a body temperature that is considerably greater than that of the surrounding water due to their high metabolic rate. Turtles, like other reptiles, birds, and mammals, are categorized as amniotes. Turtles, like other amniotes, breathe air and do not lay eggs underwater, despite the fact that many species live in or near water.

Turtles have been depicted in mythology and folklore from all across the world. Pets are kept for a variety of terrestrial and watery animals. Turtles have been killed for their flesh, as well as their carapaces, which have been used in traditional medicine. Marine turtles are frequently caught in fishing nets and killed bycatch. Turtle habitats are being destroyed all around the world. Many species are threatened with extinction by 2100 as a result of these forces.

A turtle’s shell is the only one of its kind among vertebrates, and it protects the animal from the environment. It is largely formed of bone and is divided into two sections: the carapace, which typically includes 50–60 bones and covers the animal’s back, and the plastron, which has 7–11 bones and covers the animal’s belly. They are linked by the plastron’s lateral extensions. The vertebrate and ribs merge to create the carapace, whereas the plastron is made up of bones from the shoulder girdle, sternum, and gastralium. The shoulder girdle was once assumed to be located inside the rib cage, but it is really located in front of the rib cage, with the shoulder blade orientated vertically, as it was in other reptiles.

Scutes, which are epidermal scales formed of keratin, the same material that makes up hair and fingernails, cover the shell’s exterior surface. A turtle’s carapace has 38 scutes and the plastron has 16, for a total of 54 scutes. “Marginals” are located along the margin, “vertebrals” are found across the vertebral column (the first one near the neck is termed the “cervical”), and “pleurals” are found between the marginals and vertebrals. The gulars (throat), humerals, and abdominals are all scutes of the plastron. Turtle scutes generally interlock like mosaic tiles, however the scutes on the carapace of some species, such as the hawksbill sea turtle, can overlap.

Turtles’ tails are shorter than those of other reptiles. They can, however, differ in length and thickness across species and sexes. Snapping turtles and the big-headed turtle, which utilizes its tail to support itself when climbing, have particularly enormous tails. The cloaca lies at the base of the turtle’s tail, and the tail itself houses the reproductive organs. As a result, males’ tails are longer to accommodate the penis. The tail of sea turtles is longer and prehensile, and it is used to grip the female during mating. The tails of some turtle species contain spines.

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