Turtle

Turtles belong to the order Testudines. They are a unique group of reptiles defined by a specialized shell. This shell provides both protection and shelter from the environment. There are 360 living and recently extinct species of turtles. These include land-dwelling tortoises and freshwater terrapins.

Modern turtles are divided into two major groups. These are the Pleurodira, or side-necked turtles, and the Cryptodira, or hidden-necked turtles. They are distinguished by how they retract their heads into their shells.

The turtle shell is a complex anatomical structure.

It consists of 50 to 60 bones. The upper, domed part is called the carapace. The flatter underside is the plastron, or belly-plate. These parts are connected by lateral extensions of the plastron. The carapace is fused with the vertebrae and the ribs. During development, the ribs grow sideways into a carapacial ridge. This ridge supports the carapace as it forms. Proteins called fibroblast growth factors, such as FGF10, signal this growth. The outer surface is covered in keratin scutes. Keratin is the same material found in hair and fingernails.

Different environments have shaped the variety of turtle shells. Land-dwelling turtles often have dome-shaped shells. This shape helps them resist being crushed by large animals. Aquatic turtles typically have flatter, smoother shells. This shape allows them to cut through water more easily. Sea turtles have streamlined shells to reduce drag in the open ocean. Some species have even evolved spikes or lumps for camouflage or protection.

Some turtles, like box turtles, have shells where the bones are fully fused. Others, known as softshell turtles, have rubbery edges because they lack certain bones. The leatherback sea turtle is unique because it has very little bone in its shell. Instead, it uses thick connective tissue and leathery skin.

Turtles have a long history of scientific study and naming. The name Testudines was coined by the German naturalist August Batsch in 1788. This name is based on the Latin word for tortoise. The order has also been called Chelonii and Chelonia. These names come from the Ancient Greek word for tortoise. The term chelonian is often used as a formal name for members of the group.

Naming conventions can vary by region. In Britain, "turtle" usually refers to sea turtles. In Australia, the term "turtle" is now often used for the entire group. In North America, the name may refer to the entire order.

Turtles exhibit an incredible range of sizes.

The leatherback turtle is the largest living species. It can reach over 2 meters in length and weigh over 600 kilograms. The largest known prehistoric turtle was Archelon ischyros. It lived during the Late Cretaceous and was up to 4 meters long. It is estimated to have weighed over 2,000 kilograms. Conversely, the smallest living turtle is Chersobius signatus from South Africa. It measures no more than 8 centimeters and weighs very little.

Locomotion and feeding habits vary greatly among species.

Turtles are ectotherms, meaning their internal temperature follows the environment. Most are opportunistic omnivores. They eat plants and animals with limited movement. Some species have very powerful bites. The durophagous Mesoclemmys nasuta has a bite force of 1,100 newtons. Because they lack teeth, they use keratin beaks to eat. Sea turtles are specialized swimmers. They use their front limbs like wings to create thrust. This makes them much faster and more efficient than freshwater turtles.

Despite their resilience, many turtles face significant threats.

Habitat destruction is a major problem for many species. Some turtles are hunted for their meat, shells, or for traditional medicine. Sea turtles are also frequently killed as bycatch in fishing nets. These pressures have caused many species to become extinct or threatened. Protecting their habitats is essential for their survival. Understanding their unique biology helps us better protect these ancient reptiles.