Added 14 September 2003.

A Rough Guide to

THE CHELONIAN FAMILIES

What follows is a rough guide to the various chelonian families around the world. This is technically known as the taxonomic classification of chelonians. Apart from the interest value, it may help you when trying to ascertain care requirements for a particular tortoise, turtle or terrapin.

The various tortoises, turtles and terrapins together form the Order Chelonia. The order is divided into two suborders, the Cryptodira (those chelonians that can pull their heads inside the shell by bending the neck in a vertical "S" shape), and the Pleurodira (the other chelonians, who pull their heads in by bending their necks in a horizontal "S" shape). This latter group, which is much smaller in numbers than the Cryptodira, is sometimes referred to collectively as "sideneck turtles".

Below this, the suborders are divided into four and one superfamilies respectively, with the exception of the Chelydridae (Snapping Turtles) and the Chelidae (Australo-American Sideneck Turtles) who form their own families outside the superfamilies.

Chelonian taxonomy is not subject to the same fervid amount of revision that lizard, snake and frog classifications are, but even so there is still debate and discussion over the relationships between the species, especially with DNA analysis, molecular biology and the relatively new science of cladistics now in place. Although the classification that follows is broadly correct (I have borrowed largely from David Alderton's Turtles and Tortoises of the World, 1989 and made revisions in the light of information on the EMBL reptile database and the World Chelonian Trust), you should be aware that it may change or that there are alternative models. Lest this sound too vague and woolly to be worth reading, I should add that the family descriptions at least are fairly accurate.

The term Old World is used here according to standard usage to include Europe, Africa, Asia and Australia. The term New World denotes the Americas.

The italicised name in brackets is the proper Latin scientific name.

Suborder Cryptodira (Straight-Necked Turtles)

Snapping Turtles (Family Chelydridae: 3 species)

This is a small family of quite large aquatic turtles that includes the alligator- and common snapping turtle of the Americas, plus the Big-Headed Turtle, Platysternon, of SE Asia. None of these turtles can withdraw their head into the protection of the shell, but then the snappers at least are aggressive and big enough to take care of themselves.

See also Chelydridae

Superfamily Testudinoidea

Family Emydidae (Freshwater Turtles: Pond Turtles, Box & Water Turtles)

Freshwater turtles, distributed in North America and Europe.

See Emydidae.

Family Testudinidae (Tortoises)

These are the familiar and much-loved land tortoises. They include the familiar Mediterranean tortoises as well as the unusual, flexible-shelled Pancake Tortoise and the extremely long-lived Giant Tortoises of the Galapagos.

See Testudinidae

Family Bagaturidae/Geoemydidae (Asian River Turtles, Leaf & Roofed Turtles, Asian Box Turtles)

There seems to be some disagreement about the status of the genera and species within this group: one source, for example (the EMBL database) has this listed as Family Bagaturidae on the hyperlink, only for it then to become Family Geoemydidae (subfamilies Bagaturinae and Geomydinae), while the World Chelonian Trust lists it as Family Geoemydidae with no subfamilies. Therefore we are tentatively hedging our bets until we can get hold of the relevant literature. It makes no difference to the species anyway.

See Bagaturidae.

Superfamily Trionychidae

Family Carettochelyidae (Pig-Nose Turtles)

Contains a single species, the Pig-Nose Turtle of New Guinea and Australia, Carettochelys. This species has some affinity with true marine turtles.

Family Trionychidae (Soft-Shelled Turtles)

Aquatic turtles with flattened and non-rigid, disc-shaped shells, and paddle-like limbs with three claws. Many are rather aggressive by nature, at least if they feel threatened. They are distributed across the tropics but not in Central or South America or Australia.

See Trionychidae.

Superfamily Kinosternoidea

Family Dermatemydidae (River Turtles)

Contains a single species, the Mesoamerican River Turtle of Central America, Dermatemys.

Family Kinosternidae (Mud and Musk Turtles)

A group of small-to-medium sized, mainly aquatic turtles, found principally in the Americas but also in Asia.

See also A Guide to Kinosternidae

Superfamily Chelonioidea

Family Cheloniidae (Sea Turtles)

The sea turtles are found in practically all oceans of the world. They are truly maritime, only the females returning to land and then only to lay eggs at night before returning to the ocean. Many travel vast distances. Sea turtles are among the most endangered of animals, not only through exploitation by humans for food but also inadvertently through fishing practices and the degradation of nesting sites.

See Cheloniidae.

Family Dermochelyidae (Leatherback Turtles)

These marine turtles are unique, having the normal carapace replaced by a leathery layer. Another singular feature is that a degree of control over body temperature can be attained, unlike in most other reptiles. The sole species is Dermochelys coriacea.

Suborder Pleurodira

Family Chelidae (Australo-American Sideneck Turtles/Snake-Necked Turtles)

A riverine group distributed in Australia, New Guinea and eastern South America: some of its species are noted for the length of their necks, which in extreme cases may be as long as the shell.

See Chelidae.

Superfamily Pelomedusoides

Family Pelomedusidae (African Sideneck Turtles)

Two genera of small, darkish aquatic chelonians confined to Africa and some offshore islands [Spawls et al].

See Pelomedusidae.

Family Podocnemididae (American Sideneck Turtles)

Formerly considered part of the Family Pelomedusidae: contains river turtles found mainly in the Amazon River.

See Podocnemididae.

Bibliography

Turtles and Tortoises of the World, David Alderton, Blandford, London 1999.

Schildkröten, Gerhard Müller, Eugen Ullmer, Stuttgart 1995.

A Field Guide to the Reptiles of East Africa, Stephen Spawls, Kim Howell, Robert Drewes and James Ashe, Natural World/Academic Press, London 2002.

Links

World Chelonian Trust has a useful taxonomic guide.

EMBL reptile database likewise is an authority on the taxonomy of reptiles.

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