Testudines - turtles


Vertebrata; Gnathostomata; Osteichthyes; Sarcopterygii; Tetrapoda;
Amniota; Sauropsida; Parareptilia (formerly Anapsida); Testudines

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Testudine skeleton
Show Testudine skeleton Image
Testudine skeleton
Show Testudine skeleton Image
Testudine skeleton
Diversity and Lower Taxonomy:

The order testudines is a monophyletic clade containing 260 species of extant turtles, terrapins and tortoises in 13 families. Tortoises include just a single family (Testudinidae), which is phylogenetically embedded within the turtles. Turtles are therefore the paraphyletic group comprising the remaining 12 families (they are paraphyletic as their last common ancestor is shared with that of tortoises).

Extant testudines are divided into two clades, the Cryptodira (meaning "hidden neck") and thePleurodira (meaning "side neck"), categorised by a difference in the articulation of the cervical vertebrae.The Pleurodira, containing the 3 families of side-necked turtles, can fold their necks medio-laterally, while cryptodires - the remaining families, including the tortoises - fold their necks dorso-ventrally.

Distribution and Habitat:

Testudines species are terrestrial, aquatic or semi-aquatic and occupy many different habitats within these systems, from the open ocean to freshwater rivers, tropical rainforests and deserts (Pough et al., 2009).

The distribution of Pleurodires is restricted to the Southern Hemisphere (South America, Australia, New Guinea) where all species are either aquatic or semi-aquatic.

The Crpytodires, on the other hand, can be found in both the Northern and parts of the Southern hemisphere (South America and Africa) (Pough et al., 2009), and may be terrestrial (e.g., Hermann's tortoise, Testudo hermanni), freshwater (e.g., European pond turtle, Emys orbicualris), or marine (e.g., leatherback sea turtle, Dermochelys coriacea).

Testudines are predominantly found in tropical and temperate regions, although it is believed the migratory route of some leatherbacks may pass close to the Arctic Circle (Sherrill-Mix, 2008). The Testudinidae (tortoises, or land turtles) are most speciose in Sub-Saharan Africa, but the greatest diversity of all turtles is found in South America - specifically, in the Rio Negro region of the Amazon basin (Buhlman et al., 2009).

Conservation Status (IUCN):

In the 2008 IUCN Red List, 63% (132 species) of Testudines are categorised as threatened with extinction, and 6 species are listed as extinct, including Cylindraspis indica, C. inepta, C. peltastes, C. vosmaeri, and Pelusios seychellensis (Bonin et al., 2006).

Historically, this ancient group have always been prized and captured for their meat, shell and skin. Today, many species are threatened with extinction from over-exploitation, with illegal trade taking place unregulated (Buhlman et al., 2009). Turtles are commercially valuable, particularly in China, as a delicacy and medicine. Significant numbers are also killed as by-catch. Habitat loss and degradation, particularly of nesting sites, is a major threat (Buhlman et al., 2009), and pollution of freshwater and marine ecosystems as well as climate change are growing problems (Bonin et al., 2006).

Testudines have a very slow growth rate, reach sexual maturity late and, although they produce a high number of offspring, their initial rate of survival is low. This life history means populations are vulnerable to extinction as any depletion in numbers can have long lasting or irreparable effects (Pough et al., 2009).


  • The skull has no temporal fenestrae (openings in the skull near the temples) - the anapsid condition - unlike all other extant amniotes - mammals have one (synapsid), and other reptiles have two (diapsid).
  • The trunk is surrounded by a two layered shell - carapace (dorsal) and plastron (ventral) - composed largely of dermal bone (fused with the ribs and vertebrae in the carapace). The carapace is also covered with an epidermal component - a layer of broad, horny scales called scutes. Note in the photographs the plastron has been removed and attached to the carapace to allow the skeleton to be seen.
  • The limb girdles are uniquely incorporated into the rib cage. This is due to the fact that they are housed within the carapace, which is derived partly from the rib bones and thoracic vertebrae.
  • They have evolved a horny beak instead of teeth.


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