turtle

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leatherback sea turtle (Dermochelys coriacea)

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turtle summary

Classification

in turtle

Also known as: Chelonia, Testudines

Written by George R. Zug

Fact-checked by The Editors of Encyclopaedia Britannica

Last Updated: Jun 8, 2025 • Article History

Related Topics:: snake-necked turtle; side-necked turtle; pond turtle; What Are Turtle Shells Made Of?; Cryptodira

On the Web:: PetMD - Aquatic Turtle Care Sheet (June 07, 2025)

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Satellite tracking of 12,000 marine animals reveals ocean giants are in trouble • June 7, 2025, 7:50 PM ET (ScienceDaily)

Blanding's turtle (Emydoidea blandingii) — Blanding's turtle (*Emydoidea blandingii*)Blanding's turtle (*Emydoidea blandingii*), a species native to the Great Lakes region and adjacent river systems in North America, has been classified as an endangered species by the International Union for Conservation of Nature since 2013.

The title of the turtle order was formerly Testudinata, although the term Chelonia was also regularly used. In the 1950s, priority was given to the Linnaean name Testudines as the formal name for the turtle order. The manner in which the neck folds is the most obvious feature separating the two modern turtle suborders. Lower levels of taxonomy are defined mainly by differences in the skeleton, primarily the skull and shell. The following classification of living families derives mainly from Turtles of the World, 8th ed. (2017), by the Turtle Taxonomy Working Group of the IUCN.

Order Testudines (turtles)
356 species found on all continents except Antarctica and in tropical and subtropical oceans and seas.
- Suborder Cryptodira (vertical-necked, or S-necked, turtles)
  263 species in 11 families.
  - Superfamily Testudinoidea
    190 species in 4 families.
    - Family Emydidae (pond, box, Blanding’s, painted, spotted, and chicken turtles)
      53 species in 12 genera of Europe and the Americas.
    - Family Platysternidae (big-headed turtles)
      1 species of Southeast Asia.
    - Family Testudinidae (tortoises)
      65 species in 18 genera, mainly of Africa and Asia but also of Europe and the Americas.
    - Family Geoemydidae (Asian river turtles, leaf and roofed turtles, Asian box turtles)
      71 species in 18 genera of southern Europe to East Asia and Japan, Central America, and northern South America.
  - Superfamily Kinosternoidea
    28 species in 2 families.
    - Family Kinosternidae (mud and musk turtles, including the stinkpot)
      27 species in 5 genera of North and South America.
    - Family Dermatemydidae (Mesoamerican river turtle)
      1 species of Central America.
  - Superfamily Trionychoidea
    33 species in 2 families.
    - Family Trionychidae (softshell turtles)
      32 species in 13 genera of North America, Africa, and South Asia to New Guinea.
    - Family Carettochelyidae (pignose turtle)
      1 species of Southern New Guinea and northern Australia.
  - Superfamily Chelonioidea
    7 species in 2 families.
    - Family Cheloniidae (sea turtles, including the loggerhead, ridley, hawksbill, and green sea turtles)
      6 species in 5 genera of tropical oceans worldwide.
    - Family Dermochelyidae (leatherback turtle)
      1 species found in tropical to temperate oceans worldwide.
  - Family Chelydridae (snapping turtles)
    5 species in 2 genera; family not assigned to a superfamily.
- Suborder Pleurodira
  93 species in 3 families.
  - Family Chelidae (snake-necked turtles, including the matamata)
    58 species in 14 genera of South America, Australia, New Guinea; family not assigned to a superfamily.
  - Family Pelomedusidae (side-necked turtles)
    27 species in 2 genera of Africa.
  - Family Podocnemididae (Madagascan big-headed turtles and American side-necked river turtles, including the arrau)
    8 species in 3 genera of Madagascar and northern South America.

George R. Zug The Editors of Encyclopaedia Britannica

What Are Turtle Shells Made Of?

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What Are Turtle Shells Made Of?

Written and fact-checked by The Editors of Encyclopaedia Britannica

Last Updated: Apr 14, 2025 • Article History

Related Topics:: bone; turtle; shell

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Turtle shells are made of bone and cartilage, but it is the form and function of the shells that make them unique in the animal kingdom.

The top part of the shell is called the carapace while the underside is known as the plastron. Both parts are formed from two types of bone: dermal bones, which develop in the skin, and endochondral bones, which develop from cartilage and are part of the skeleton. The carapace includes 10 vertebrae and their ribs, which are overlain by and fused to dermal plates. The plastron usually contains four pairs of large plates and a single one centered near the front, all of which are classified as dermal bones.

The carapace and plastron are joined along each side of the body, creating a rigid skeletal box that houses internal organs. The turtle keeps this box throughout its life. Unlike the skin of some other reptiles, turtles cannot shed their shells. Turtle shells have evolved to not only provide protection but also to be an integral part of their skeletal structure allowing them to move. The shell’s shape and structure can vary among turtle species, with some having streamlined shells for swimming and others having domed shells for land-based living.

The Editors of Encyclopaedia Britannica