Turtles are diapsids of the order Testudines (or Chelonii) characterized by a special bony or cartilaginous shell developed from their ribs and acting as a shield. “Turtle” may refer to the order as a whole (American English) or to fresh-water and sea-dwelling testudines (British English). The order Testudines includes both extant (living) and extinct species. The earliest known members of this group date from 220 million years ago, making turtles one of the oldest reptile groups and a more ancient group than snakes or crocodilians. Of the 356 known species alive today, some are highly endangered.
- Kingdom: Animalia
- Phylum: Chordata
- Class: Reptilia
- Clade: Testudinata
- Order: Testudines
- Subgroups: Cryptodira
With so many different types of turtle, there is no average size. The largest sea turtle species is the leatherback turtle. It weighs 600 to 1,500 lbs. (272 to 680 kilograms) and is about 4.5 to 5.25 feet (139 to 160 centimeters) long, according to the World Wildlife Federation (WWF). The Galápagos tortoise grows up to 6 feet (183 cm) long and 573 lbs. (260 kg), according to the San Diego Zoo. The largest freshwater turtle in North America is the alligator snapping turtle. It can grow to 2.5 feet (80 cm) long and weigh as much as 200 lbs. (91 kg). The Yangtze giant softshell turtle is the largest softshell turtle. It measures up to 3.6 feet (1 m) across, and weigh up to 309 lbs. (140 kg).
Turtles and tortoises are reptiles, the only ones to have a shell. Their bodies are protected by a shell on top and underneath. Their backbone, breastbone and ribs have become part of the shell, so they cannot remove their shells. The shell underneath is called a plastron, and the upper and under shells are joined by a piece called a bridge.
Most turtles that spend most of their lives on land have their eyes looking down at objects in front of them. Some aquatic turtles, such as snapping turtles and soft-shelled turtles, have eyes closer to the top of the head. These species of turtle can hide from predators in shallow water, where they lie entirely submerged except for their eyes and nostrils. Near their eyes, sea turtles possess glands that produce salty tears that rid their body of excess salt taken in from the water they drink.
Turtles are not social animals. Although members of the same species may be observed congregating along a stream or basking on a log, there is usually little interaction between individuals. Several species may inhabit the same river or lake, but each has different foods, feeding behaviours, and likely different activity periods. For example, a small lake in Georgia may be home to at least seven turtle species: snapping, red-eared sliders, eastern cooters, common mud turtles, loggerhead musk, stinkpots (common musk turtles), and spiny softshell turtles.
Sea turtles live in almost every ocean basin throughout the world, nesting on tropical and subtropical beaches. They migrate long distances to feed, often crossing entire oceans. Some loggerheads nest in Japan and migrate to Baja California Sur, Mexico to forage before returning home again. Leatherbacks are capable of withstanding the coldest water temperatures (often below 40˚F) and are found as far south as Chile and as far north as Alaska.
Turtles are thought to have exceptional night vision due to the unusually large number of rod cells in their retinas. Color vision with a wealth of cone subtypes with sensitivities ranging from the near ultraviolet (UVA) to red. Some land turtles have very poor pursuit movement abilities, which are normally found only in predators that hunt quick-moving prey, but carnivorous turtles are able to move their heads quickly to snap.
While typically thought of as mute, turtles make various sounds when communicating. Tortoises may be vocal when courting and mating. Various species of both freshwater and sea turtles emit numerous types of calls, often short and low frequency, from the time they are in the egg to when they are adults. These vocalizations may serve to create group cohesion when migrating.
- Sea turtle
- Asian box turtle
Also more: African Dwarf Frog