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Kinixys (Hinged-Back Tortoises)

GCTTS Member Ann Smylie

There are many turtles that have a movable hinge on the plasteron, but the Hinge-Back Tortoise (genus - Kinixys) is the only living turtle where the hinge has developed across the back of the carapace. This broad band of flexible connective tissue is located between the 4th and 5th costals and the 7th and 8th peripherals in adults.

Hatchlings of this African tortoise are flattened with serrated marginals. The hinge begins to develop when they are one year old.

This movable hinge provides protection by closing off the tortoise's hind legs and tail and it may also assist in egg laying and respiration.

Hinge-Backs have legs that are not as club shaped as other Testudinidae. They are long and slender giving the tortoise an unusual gait when it walks. Hinge-Backs are all omniverous and their tails end in a claw like tubercle. Males have longer, thicker tails than the females and they have concave plasterons. Hinge-Back Tortoises have relatively long skulls, a hooked upper jaw and four or five claws on each forefoot.

Different species of Hinge-Back Tortoises are found in Africa. Two of these - Kinixys Homeana and Kinixys Erosa, are similar and are found in the same areas, in west and central Africa. Both are forest dwellers, with Kinixys Erosa preferring a more moist environment. It is often found in marshes and on river banks and is a fair swimmer. They both have solid dark brown to tan shells, some with yellow markings.

Kinixys Erosa has thick paired gulars that extend beyond the carapace rim and it is also the largest species of the genus, often reaching a carapace length of 13 inches.

Both Kinixys Erosa and Kinixys Homeana have a carapace with flared marginals.

The most distinctive feature of Kinixys Hormeana is the back of the carapace which drops off abruptly, seeming to be cut off. This has earned it the German name of "clipped tortoise".

Kinixys Belliana (Bell's Hinge-Back Tortoise) is the most widely distributed and best known of the species of Hinge-Backs. It prefers the dry savannas and grasslands that skirt Africa's rainforests, where there are distinct wet and dry seasons. They become active with the onset of rains and probably lay eggs at this time. During dry periods it estivates in the muddy bottoms of drying water holes. This Hinge-Back's carapace is domed with a flat dorsal surface and sloping sides. It's anterior and posterior marginals are not flared. The center of each carapacial scute is yellow to reddish brown, surrounded by dark brown or black. The plasteron is yellow with black radiation. Its head is brown, black, yellow or tan and the limbs and tail are grayish brown.

Four subspecies of Kinixys Belliana are recognized:

Kinixys Belliana Belliana is found in eastern Africa from Somalia to South Africa. Kinixys Belliana Spekii lives in southern and central Africa and Kinixys Belliana Mertensi lives in northern Zaire and Uganda. Kinixys Belliana Nogueyi is found in west Africa and unlike the other 3 sub-species who have 5 claws on each forefoot, it has only 4.

Little is known of the small Hinge-Back Kinixys Natalensis (Natal Hinge-Back Tortoise). It inhabits dry scrubby slopes and grasslands from Mozambique, south through South Africa. Its carapace is slightly domed with a flat dorsal surface and sloping sides. The posterior and anterior marginals are not flared. Its carapacial scutes have yellow to orange centers surrounded by dark brown or black. The plasteron scutes have yellow centers and seam borders surrounded by black or brown and the head, tail and limbs are brown to yellow.



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Bob Smither 2002-06-26