Skip to main content
- Turtles are reptiles of the order Testudines (or Chelonii) characterised 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.
- The order Testudines includes both extant (living) and extinct species.
- The earliest known members of this group date from 157 million years ago, making turtles one of the oldest reptile groups and a more ancient group than snakes or crocodilians.
- Turtles are ectotherms—their internal temperature varies according to the ambient environment, commonly called cold-blooded.
- However, because of their high metabolic rate, leatherback sea turtles have a body temperature that is noticeably higher than that of the surrounding water.
- 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 North America, all chelonians are commonly called turtles, including terrapins and tortoises.
- Most land-dwelling chelonians are in the Testudinidae family, only one of the 14 extant turtle families.
- Freshwater turtles are generally smaller, but with the largest species, the Asian softshell turtle Pelochelys cantorii, a few individuals have been reported up to 6.6 ft.
- Turtles are divided into two groups according to how they withdraw their necks into their shells.
- Although many turtles spend large amounts of their lives underwater, all turtles and tortoises breathe air, and must surface at regular intervals to refill their lungs.
- The first proto-turtles are believed to have existed in the late Triassic Period of the Mesozoic era, about 220 million years ago, and their shell, which has remained a remarkably stable body plan, is thought to have evolved from bony extensions of their backbones and broad ribs that expanded and grew together to form a complete shell that offered protection at every stage of its evolution, even when the bony component of the shell was not complete.
- More recent morphological phylogenetic studies with this in mind placed turtles firmly within diapsids, slightly closer to Squamata than to Archosauria.
- All molecular studies have strongly upheld the placement of turtles within diapsids; some place turtles within Archosauria, or, more commonly, as a sister group to extant archosaurs, though an analysis conducted by Lyson et al. (2012) recovered turtles as the sister group of lepidosaurs instead.
- A molecular analysis of 248 nuclear genes from 16 vertebrate taxa suggests that turtles are a sister group to birds and crocodiles.
- The Cryptodira is the larger of the two groups and includes all the marine turtles, the terrestrial tortoises, and many of the freshwater turtles.
Was this article helpful to you?