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There are fourteen extant
families In human society A society is a Social group, group of individuals involved in persistent Social relation, social interaction, or a large social group sharing the same spatial or social territory, typically subject to the same Politi ...
of the
order Order, ORDER or Orders may refer to: * Orderliness Orderliness is a quality that is characterized by a person’s interest in keeping their surroundings and themselves well organized, and is associated with other qualities such as cleanliness a ...
Testudines, an order of
reptile Reptiles, as most commonly defined, are the animals in the class Class or The Class may refer to: Common uses not otherwise categorized * Class (biology), a taxonomic rank * Class (knowledge representation), a collection of individuals or ...

reptile
known as
turtle Turtles are an order Order, ORDER or Orders may refer to: * Orderliness Orderliness is a quality that is characterized by a person’s interest in keeping their surroundings and themselves well organized, and is associated with other qu ...

turtle
s. The testudines are some of the most ancient reptiles alive, with only the
tuatara Tuatara (''Sphenodon punctatus'') are reptiles Endemism, endemic to New Zealand. Although resembling most lizards, they are part of a distinct lineage, the order Rhynchocephalia. Their name derives from the Māori language, and means "peaks on ...

tuatara
s considered more primitive. There are approximately 300
extant species Neontology is a part of biology Biology is the natural science that studies life and living organisms, including their anatomy, physical structure, Biochemistry, chemical processes, Molecular biology, molecular interactions, Physiology, ph ...
and 97
genera Genus /ˈdʒiː.nəs/ (plural genera /ˈdʒen.ər.ə/) is a taxonomic rank In biological classification In biology, taxonomy () is the scientific study of naming, defining (Circumscription (taxonomy), circumscribing) and classifying gr ...
of testudines, split into two suborders: the
Cryptodira The Cryptodira ('' el, hidden neck'') are a suborder of Testudines that includes most living tortoises and turtles. Cryptodira differ from Pleurodira (side-necked turtles) in that they lower their necks and pull the heads straight back into the ...
ns and the
Pleurodira The Pleurodira are one of the two living suborder In biological classification, the order ( la, wikt:ordo#Latin, ordo) is # a taxonomic rank used in the classification of organisms and recognized by the nomenclature codes. The well-known rank ...
ns. The distinction between these two suborders is based on the mode in which they cover their head and neck. The Pleurodirans, also called the side-necked turtles, have long necks, and fold them sideways to align them with the shell. The
Pelomedusidae :''Alternatively, "Pelomedusidae" may refer to the Pelomedusoidea. See #Systematics and taxonomy, below for details.'' Pelomedusidae is a family (biology), family of freshwater turtles native to sub-Saharan Africa, with a single species, ''Pelom ...
and
Chelidae Chelidae is one of three living families of the turtle suborder Pleurodira, and are commonly called Austro-South American side-neck turtles. The family is distributed in Australia, New Guinea, parts of Indonesia, and throughout most of South Amer ...
are the only extant families of pleurodires. The Cryptodirans pull their neck straight back to conceal their head within the shell. The
Carettochelyidae The pig-nosed turtle (''Carettochelys insculpta''), also known as the pitted-shelled turtle or Fly River turtle, is a species of turtle native to northern Australia and southern New Guinea. It is the only living member of the family Carettochely ...
,
Cheloniidae Cheloniidae is a family of typically large marine turtles that are characterised by their common traits such as, having a flat streamlined wide and rounded shell and almost paddle-like flippers for their forelimbs. The six species that make up th ...
,
Chelydridae The Chelydridae is a Family (biology), family of turtles that has seven extinct and two extant genera. The extant genera are the snapping turtles, ''Chelydra'' and ''Macrochelys''. Both are Endemic (ecology), endemic to the Western Hemisphere. Th ...
,
Dermatemydidae
Dermatemydidae
,
Dermochelyidae Dermochelyidae is a family In human society, family (from la, familia) is a group of people related either by consanguinity (by recognized birth) or affinity (by marriage or other relationship). The purpose of families is to maintain the ...
,
Emydidae Emydidae (Latin ''emys'' (freshwater tortoise) + Ancient Greek εἶδος (''eîdos'', “appearance, resemblance”)) is a family (biology), family of testudines (turtles) that includes close to 50 species in 10 genera. Members of this family ...

Emydidae
,
Kinosternidae The Kinosternidae are a family (biology), family of mostly small turtles that includes the mud turtles and musk turtles. The family contains 25 species within four genus, genera, but Taxonomy (biology), taxonomic reclassification is an ongoing pro ...
, Testudinidae and
Trionychidae The Trionychidae are a taxonomic Taxonomy (general) is the practice and science of classification of things or concepts, including the principles that underlie such classification. The term may also refer to a specific classification scheme. O ...
are all cryptodires, although the ability to retract the head has been lost in the sea turtles (Cheloniidae and Dermochelyidae). A third order, the
Paracryptodira __NOTOC__ Paracryptodira is an extinct group of reptiles in the clade A clade (), also known as a monophyletic group or natural group, is a group of organism In biology, an organism () is any organic, life, living system that functi ...
ns, are extinct. Reptiles are classified according to the pattern of
fenestration Fenestration may refer to: * Fenestration (architecture), the design, construction, or presence of openings in a building * Used in relation to fenestra in anatomy, medicine and biology * Fenestration, holes in the rudder of a ship to reduce the wo ...
in the temporal region of the
skull The skull is a bone A bone is a rigid tissue Tissue may refer to: Biology * Tissue (biology), an ensemble of similar cells that together carry out a specific function * ''Triphosa haesitata'', a species of geometer moth found in North A ...

skull
. Testudines are placed in the subclass
Anapsida An anapsid is an amniote Amniotes (from Greek ἀμνίον ''amnion'', "membrane surrounding the fetus", earlier "bowl in which the blood of sacrificed animals was caught", from ἀμνός ''amnos'', "lamb") are a clade A clade (; fro ...
because they lack fenestration. There are suggestions that this lack of fenestration is a secondary characteristic and that turtles belong in
Diapsida Diapsids ("two arches") are a group of amniote Amniotes (from Greek ἀμνίον ''amnion'', "membrane surrounding the fetus", earlier "bowl in which the blood of sacrificed animals was caught", from ἀμνός ''amnos'', "lamb") are a cla ...
. Both sides cite strong evidence, and the conflict has yet to be resolved. The shell of testudines distinguishes them from other vertebrates. The shell is not an
exoskeleton An exoskeleton (from Greek έξω, ''éxō'' "outer" and σκελετός, ''skeletós'' "skeleton") is the external skeleton A skeleton is a structural frame that supports an animal Animals (also called Metazoa) are multicellular ...

exoskeleton
, but a modified
ribcage The rib cage is the arrangement of rib In vertebrate anatomy, ribs ( la, costae) are the long curved bones which form the rib cage, part of the axial skeleton. In most tetrapods, ribs surround the chest, enabling the lungs to expand and thus fa ...
and part of the
vertebral column The vertebral column, also known as the backbone or spine, is part of the axial skeleton Axial may refer to: * one of the describing relationships in an animal body * and submarine volcano off Oregon, USA * , a ghost town * In geometry: :* ...

vertebral column
. Because of the shell, the pectoral and pelvic girdles are located within the ribcage. The limb bones are also modified to accommodate to the shell. The earliest known turtles are from fossils in the
Upper Triassic The Late Triassic is the third and final epoch In chronology 222px, Joseph Scaliger's ''De emendatione temporum'' (1583) began the modern science of chronology Chronology (from Latin Latin (, or , ) is a classical language belonging to ...
. These fossils are nearly indistinguishable from modern turtles anatomically. In these early fossils (mostly of the genus
Proganochelys ''Proganochelys'' is an extinct, primitive stem-turtle that has been hypothesized to be the sister taxon In biology Biology is the natural science that studies life and living organisms, including their anatomy, physical structure, Bi ...
), the teeth have already been lost, and a
keratin Keratin () is one of a family of structural fibrous proteins also known as ''scleroproteins''. Alpha-keratin Alpha-keratin, or α-keratin, is a type of keratin Keratin () is one of a family of fibrous structural proteins known as Scleroprot ...

keratin
beak is suggested by the
mandible In anatomy Anatomy (Greek ''anatomē'', 'dissection') is the branch of biology concerned with the study of the structure of organisms and their parts. Anatomy is a branch of natural science which deals with the structural organization of li ...

mandible
s. Important differences between Proganochelys and modern turtles are the presence of the palatal teeth (lost in modern species), the inability to retract the head within the shell, and the lack of a trochlear pulley in the jaw closing anatomy.


Families

The following lists the family—the Latin name of the family, date in which the species was formally described and classified, and the binomial authority on the species; the number of genera belonging to the family; the name or names commonly used; an example species and an example image. , - ,
Emydidae Emydidae (Latin ''emys'' (freshwater tortoise) + Ancient Greek εἶδος (''eîdos'', “appearance, resemblance”)) is a family (biology), family of testudines (turtles) that includes close to 50 species in 10 genera. Members of this family ...

Emydidae

Rafinesque Constantine Samuel Rafinesque-Schmaltz (October 22, 1783September 18, 1840) was a French 19th-century polymath born near Constantinople in the Ottoman Empire and self-educated in France. He traveled as a young man in the United States, ultimately ...
, 1815
, , 12, , Pond turtles, terrapins, and sliders, ,
Red-eared slider The red-eared slider (''Trachemys scripta elegans'') is a subspecies of the pond slider The pond slider (''Trachemys scripta'') is a species of common, medium-sized, semiaquatic turtle. Three subspecies are described, the most recognizable o ...

Red-eared slider
(''Trachemys scripta elegans''), , , - ,
Geoemydidae The Geoemydidae (formerly known as Bataguridae) are one of the largest and most diverse Family (biology), families in the order Testudines (turtles), with about 70 species. The family includes the Eurasian pond and river turtles and Neotropical ...

Theobald Theobald is a Germanic name, Germanic dithematic name, composed from the elements ''theodiscus, theod-'' "people" and ''bald'' "bold". The name arrived in England with the Norman Conquest, Normans. The name occurs in many spelling variations, incl ...
, 1868
, , 24, , Asian leaf turtles, roofed turtles, and Asian box turtles, , Amboina box turtle (''Cuora amboinensis''), , , - ,
Kinosternidae The Kinosternidae are a family (biology), family of mostly small turtles that includes the mud turtles and musk turtles. The family contains 25 species within four genus, genera, but Taxonomy (biology), taxonomic reclassification is an ongoing pro ...

Agassiz Jean Louis Rodolphe Agassiz (; ) FRS (For) FRSE (May 28, 1807 – December 14, 1873) was a Swiss-born American biologist and geologist who is recognized as an innovative and prodigious scholar of Earth's natural history. Spending his early lif ...

Agassiz
, 1857
, , 4, , Mud and musk turtles, , (''Sternotherus odoratus''), , , - , Platysternidae
Gray Grey or gray (American English American English (AmE, AE, AmEng, USEng, en-US), sometimes called United States English or U.S. English, is the set of varieties of the English language native to the United States. Currently, American En ...
, 1869
, , 1, , Big-headed turtle, ,
Big-headed turtle The big-headed turtle (''Platysternon megacephalum'') is a species of turtle Turtles are an of s known as Testudines, characterized by a developed mainly from their ribs. Modern turtles are divided into two major groups, the s and whi ...
(''Platysternon megacephalum''), , , - , Testudinidae
Batsch August Johann Georg Karl Batsch (28 October 1761 – 29 September 1802) was a German naturalist Natural history is a domain of inquiry involving organism In biology Biology is the natural science that studies life and livin ...

Batsch
, 1788
, , 12, ,
Tortoises Tortoises () are reptiles Reptiles, as most commonly defined, are the animals in the class Class or The Class may refer to: Common uses not otherwise categorized * Class (biology), a taxonomic rank * Class (knowledge representation), ...

Tortoises
, ,
Aldabra giant tortoise The Aldabra giant tortoise (''Aldabrachelys gigantea''), from the islands of the Aldabra Aldabra is the world's second-largest coral Corals are marine invertebrates Marine invertebrates are the invertebrates that live in marine habitats ...
(''Geochelone gigantea''), , , - ,
Trionychidae The Trionychidae are a taxonomic Taxonomy (general) is the practice and science of classification of things or concepts, including the principles that underlie such classification. The term may also refer to a specific classification scheme. O ...

Fitzinger, 1826, , 14, , Softshell turtles, , Spiny softshell turtle (''Apalone spinifera''), , , - , colspan="5" align="center" bgcolor="#BBBBFF",
Pleurodira The Pleurodira are one of the two living suborder In biological classification, the order ( la, wikt:ordo#Latin, ordo) is # a taxonomic rank used in the classification of organisms and recognized by the nomenclature codes. The well-known rank ...
– 3 families, 16 genera, over 60 species , - !Family!!Genera!!Common names!!Example species!!Example image , - ,
Chelidae Chelidae is one of three living families of the turtle suborder Pleurodira, and are commonly called Austro-South American side-neck turtles. The family is distributed in Australia, New Guinea, parts of Indonesia, and throughout most of South Amer ...

Gray Grey or gray (American English American English (AmE, AE, AmEng, USEng, en-US), sometimes called United States English or U.S. English, is the set of varieties of the English language native to the United States. Currently, American En ...
, 1831
, , 15, , Austro-American sideneck turtles, , Common snakeneck turtle (''Chelodina longicollis''), , , - ,
Pelomedusidae :''Alternatively, "Pelomedusidae" may refer to the Pelomedusoidea. See #Systematics and taxonomy, below for details.'' Pelomedusidae is a family (biology), family of freshwater turtles native to sub-Saharan Africa, with a single species, ''Pelom ...

Cope The cope (known in Latin as ''pluviale'' 'rain coat' or ''cappa'' 'cape') is a liturgical vestment, more precisely a long mantle or cloak, open in front and fastened at the breast with a band or clasp. It may be of any liturgical colours, litu ...
, 1868
, , 2, , Afro-American sideneck turtles, ,
African helmeted turtle The African helmeted turtle (''Pelomedusa subrufa''), also known commonly as the marsh terrapin, the crocodile turtle, or in the pet trade as the African side-necked turtle, is a species of omnivorous Pleurodira, side-necked terrapin in the Famil ...
(''Pelomedusa subrufa''), , , - ,
Podocnemididae Podocnemididae is a family (biology), family of Pleurodira, pleurodire (side-necked) turtles, once widely distributed. Most of its 20 genera and 30 species are now extinct. Seven of its eight surviving species are native to South America: the gen ...

Podocnemididae

Gray Grey or gray (American English American English (AmE, AE, AmEng, USEng, en-US), sometimes called United States English or U.S. English, is the set of varieties of the English language native to the United States. Currently, American En ...
, 1869
, , 3, , Madagascar big-headed, big-headed Amazon River turtle and South American sideneck river turtles, , Madagascar big-headed turtle (''Erymnochelys madagascariensis''), ,


References


Further reading

* *


External links

* {{Featured list Testudines, * Taxonomic lists (families), Testudines Lists of reptiles, Testudines families