- For other uses, see Turtle (disambiguation).
Turtles are reptiles of the order Testudinata, most of whose body is
shielded by a special bony shell developed from their ribs. The term turtle is usually used for the aquatic species, aquatic
fresh-water turtles also being referred to as terrapins. The term is also used (esp. North America) to refer to all members of the order, including tortoises, which are predominantly land based. The order of Testudines includes both extant (living) and extinct varieties. About 300 species are alive today.
Sea turtles grow to large sizes and live in the oceans in the temperate and
tropical regions of the earth. Pond turtles (or terrapins) are generally of a much
smaller size, while land based terrapins (or tortoises) can be as big as the sea turtles. The measured sizes of turtles varies
from a few centimetres (forest/jungle species) to up to two meters (the leatherback and the galapagos tortoises). All turtles
have a protective shell around their bodies. The top part of their case is called the carapace, the underside is the plastron, and the two are connected
by the bridge. Turtles generally live a long time; some individuals are known to have lived longer than 150 years.
The first turtles already existed in the era of the dinosaurs, some 200 million
years ago. Turtles are the only surviving branch of the even more ancient clade Anapsida, which includes groups such as the procolophonoids, millerettids and pareiasaurs. All anapsid skulls lack a
temporal opening. All other extant amniotes have temporal openings (although in mammals the hole has become the zygoid arch). Most of the anapsids became extinct in the late Permian period, with the exception of the procolophonoids and the precursors
of the testudines (turtles).
However, it has recently been suggested that the anapsid condition of the turtle skull may not be a primitive character
reflecting anapsid descent, but rather a case of convergent evolution. More recent phylogenetic studies with this in mind have
placed turtles firmly within diapsids, slightly closer to Squamata than to Archosauria. All molecular studies have
strongly upheld this new phylogeny, though some place turtles closer to Archosauria. Re-analysis of prior phylogenies that affirmed an anapsid ancestry suggests that their inclusion
of turtles within Anapsida was due to both the starting assumption that they were anapsid (most prior phylogenies concerned what
sort of anapsid they were) and also due to insufficiently broad sampling of fossil and extant taxa for construction of the
cladogram. While the issue is far from resolved, most scientists now lean towards a Diapsid origin for turtles.
Even though they spend large amounts of their lives underwater, turtles are air-breathing reptiles, and must surface at
regular intervals to refill their lungs with fresh air. They also spend part of their lives on dry land. Sea turtles lay their
eggs on dry sandy beaches, and are highly endangered largely as a result of beach development and over hunting.
Aquatic respiration in Australian freshwater turtles is currently being studied. Some species have large cloacal cavities that
are lined with many finger-like projections. These projections, called "papillae", have a rich blood supply, and serve to
increase the surface area of the cloaca. The turtles can take up dissolved oxygen from the water using these papillae, in much
the same way that fish use gills to respire.
A sea turtle. Photo credit: NOAA
Order Testudines - Turtles
Suborder Cryptodira
Suborder Pleurodira
- Family Chelidae (Austro-American Sideneck Turtles)
- Superfamily Pelomedusoidea
- Family Pelomedusidae (Afro-American Sideneck Turtles)
- Family Podocnemididae (Madagascan Big-headed and American Sideneck
River Turtles)
Turtles in pop culture
Turtles are depicted in Western culture as, snapping turtles aside, an easygoing and patient creature.
The Teenage Mutant Ninja Turtles are
comic characters.
In the song Abcdefghijklmnopqrstuvwxyz, Sesame
Street character Big Bird ponders if Abcdefghijklmnopqrstuvwxyz is a "Or
strange, exotic turtle/You never see in a zoo".
Terry Pratchett's Discworld rests on the back of the gigantic star-turtle Great
A'Tuin.
The mascot of the University of Maryland, College Park is the diamondback terrapin; which is also the
state reptile of Maryland.
The Turtle (also known as Maturin) appears in a number of Stephen King's
novels, including It, and The Dark Tower series. It is a guardian of the beam, and a nursery rhyme from Roland's world
opens with "See the turtle of enourmous girth, on his shell he holds the Earth".
The Grateful Dead recorded a song entitled "Terrapin Station", which appears
on the album of the same name and was a steady inclusion in their live repertoire.
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