David T. Kirkpatrick, Ph.D
Often in nature the same type of adaptation will be found in unrelated
families of animals, attesting to the survival benefits of that particular
change. In chelonians, many families have developed a hinged plastron, which
affords greater protection to the vulnerable limbs and body of the turtle.
However, one genus, Kinixys, is unique among turtles and tortoises in
that it has turned that protective adaptation upside down. Kinixys comes
from the fusion of two Greek words: kineo (to move) and ixus (back
or waist); together they mean 'movable back'. The Hinge-back Tortoises, as they
are commonly called, develop a hinge that allows them to close the rear of their
carapace, protecting their back legs.
Hinge-back tortoises appear to be typical tortoises on first inspection.
Hinge-backs are considerably longer than they are wide, more closely resembling
a Red-footed Tortoise (Geochelone carbonaria) than a Leopard Tortoise (G.
pardalis), for example. In overall size Kinixys species are on the
smaller end of the tortoise range. The largest species, K. erosa, the
Serrated Hinge-back Tortoise, attains an adult size of 32 centimeters. The
smallest species, K. natalensis, the Natal Hinge-back Tortoise, only
grows to half that size. Hinge-backs possess the elephantine feet associated
with tortoises, although the front feet are not quite as blunt as the rear.
Their forelegs usually have a series of enlarged, downward-pointing scales while
the rear legs lack these scales. In these chelonians the head is only of medium
size, somewhat longer and flatter in profile when compared to a Leopard or a
Spurred Tortoise. Their tail ends in a nail-like spike. Of course, the
Hinge-back's distinguishing characteristic is the unique hinge that develops in
adults at the rear of the carapace, between the seventh and eighth marginal
Kinixys' carapacial hinges allow the tortoises to clamp down the rear
of their carapaces, giving increased protection to their tail and legs.
Hinge-backs also have effective defenses for their front legs and head. When
threatened, a tortoise can retract its head quite far. Its front legs then seal
the anterior opening in the carapace; the knees meet in front of the head with
the feet pointing to either side. The enlarged scales on the forelegs face
outward in this position, protecting the legs themselves and effectively closing
the tortoise off from the world.
Coloration of the carapace and plastron is quite variable in Hinge-backs,
both between species and among individuals of a particular species or
subspecies. Individuals in the various subspecies of Bell's Hinge-back,
Kinixys belliana, exhibit the greatest variation. Some shade of tan, yellow
or brown is common, with the lighter central region of each scute surrounded by
a darker shade. The coloration of Kinixys erosa is even more dramatic -
usually a dark reddish brown color predominates. In contrast, Home's Hinge-back,
K. homeana, is a much duller tan, although faint radiating lines of
darker color occasionally can be seen in some specimens. The Natal Hinge-back
often has an orange cast to it, with alternating rings of lighter and darker
material on each scute. Coloration may also vary between sexes in Hinge-backs,
with females possessing a more intense coloration or distinct pattern.
The exact number of species of Kinixys depends on the authority that
is consulted. Until fairly recently, only three species were recognized; K.
belliana, K. erosa, and K. homeana. In 1981 the species K.
natalensis was revived by Donald Broadley. Originally it had been designated
a subspecies of K. belliana. A number of subspecies have been proposed
for Bell's Hinge-back; some of these are now considered invalid and have fallen
out of favor. Others, such as K. natalensis, have been elevated to
species status. Broadley recently reviewed the genus again and indicated that
two more subspecies, K. belliana lobatsiana and K. belliana spekii,
should be listed as full species. These alterations give species status to six
tortoises: K. belliana (with three subspecies, K. b. belliana,
K. b. nogueyi, and K. b. zombensis), K. erosa, K. homeana,
K. lobatsiana, K. natalensis, and finally K. spekii(See
As might be expected from the shuffling around of species and subspecies
designations, some of the Hinge-backs are difficult to tell apart. Perhaps the
most distinctive is K. homeana, Home's Hinge-back. The posterior portion
of this tortoise's carapace has an almost 90 degree downward bend in it after
the fifth vertebral scute. Viewed from the side, it appears as if the shell
comes to a knob or point before dropping off precipitously. The scutes are
planar, meeting neighboring scutes at a distinct angle. No other Hinge-back has
this combination of features. Bell's Hinge-back, for example, has a much
smoother domed carapace without the sheer drop-off in the rear. Also, unlike
Home's Hinge-back, the rear edge of K. belliana's upper shell is smooth.
This feature distinguishes it from the Serrated Hinge-back, K. erosa. As
its common name implies, the rear carapacial edge of K. erosa is quite jagged.
The Natal Hinge-back, K. natalensis, can be identified by its small size
and by the tricuspid shape of its upper beak. Finally, K. spekii most
closely resembles K. belliana, but can be distinguished by its flatter
carapace and coloration.
Differences between the sexes in various species of Kinixys can be
somewhat subtle also. As with most other tortoises, the plastron of a male
Hinge-back is more concave and the tail is longer and thicker than in the
female. In some species the female's coloration is more vivid than the male's;
this characteristic is also age-dependent, making it somewhat unreliable
however. Another characteristic that has been mentioned as varying between the
sexes is the profile of the shell when viewed from the side. For example,
females of K. belliana and K. natalensis are believed to have a
more steeply sloped posterior profile when compared to that of a male tortoise.
Male Hinge-backs possess a territorial instinct and will battle with
suspected intruders, especially other males during breeding season. This
tendency may make it difficult to keep more than one male Hinge-back in an
enclosure. Rod Patterson, in his book Reptiles of Southern Africa,
relates a story that demonstrates the ferocity with which male Hinge-backs
defend their territory. A number of native tortoises were kept together in a
garden in South Africa. One hot afternoon a male Hinge-back went to get a drink
from a water tray and spied a Leopard Tortoise twice his size who had just
finishing drinking. "With an alacrity belying his shape the Hinged Tortoise
engaged ramming speed, making contact with the unsuspecting Leopard Tortoise
some 2 m later and hitting him so forcibly that he rolled over twice, finally
coming to rest upside-down." After inspecting the beleagured tortoise, the
Hinge-back decided that the Leopard Tortoise was no longer a threat, and went
back for his drink.
Courtship in Kinixys does not seem to be an elaborate affair. The male
will nudge and shove the female for a short while, and then mount. The shape of
the carapace presents some difficulties to successful mating, especially in
K. homeana, where the carapace comes to a sharp point and then drops off at
a right angle down to the tortoise's tail. Home's Hinge-backs owned by the
author were observed during mating. The male tortoise climbed onto the female
and then lowered his back until it was touching the ground, leaving the male
pointing upward at about a 70 degree angle to the ground. With front feet
dangling or just touching the top of the female's carapace, the male moved his
tail under the female's carapace. During mating the male stretched his neck out
as far as it would go and opened his mouth in a wide gape, emitting a number of
low moaning hisses.
The carapacial hinge in female Kinixys tortoises might help them
during egglaying. A normal clutch for Hinge-back females is two to four oval
eggs, although larger K. belliana are capable of producing twice as many
eggs. Females also can produce multiple clutches in a breeding season.
Artificially incubated eggs take between three and four months to hatch when
incubated at 30 degrees C; in the wild much longer incubation times have been
Hatchling tortoises are approximately 1.5 to 2 inches long when they first
hatch. While hatchling Bell's Hinge-backs have a smooth carapacial rim, baby
Home's and Serrated Hinge-backs have a spiny margin. Hatchling and juvenile
Hinge-backs actually do not possess a hinged carapace - the hinge develops later
in life. Young Kinixys tortoises strongly resemble tortoises in the genus
Homopus. Indeed, experts in the field can be fooled; the type specimen
for Kinixys belliana nogueyi, a juvenile, was originally placed in
Homopus until its true identity was discovered.
The Hinge-backs inhabit a diverse array of habitats in central and southern
Africa. Kinixys belliana lives primarily in grassland and savannah
regions, although some individuals can be found in coastal forests. These
regions often go through times of drought, and Bell's Hinge-back estivates
underground to survive these periods. This tortoise has large anal sacs which
can be filled with water, taking up a large percentage of the abdominal cavity,
to help it during the dry season. This stored water may be used by females when
building nests to help loosen and moisten the soil in and around the nest.
Another threat to these tortoises is fire; unfortunately carapacial hinges do
not provide adequate protection from grass fires. Grasslands also are inhabited
by Kinixys natalensis, whereas K. homeana and K. erosa
prefer forested regions. The Serrated Hinge-back especially is fond of moist
habitat, often living around marshes, wetlands and river banks. It is capable of
swimming, unlike many tortoises.
When keeping Kinixys in captivity, the wide variety of biotypes
inhabited by Hinge-backs makes it difficult for the tortoise-keeper to provide
the appropriate environment without some experimentation. However, some
generalizations can be made. Hinge-backs are relatively active tortoises, so a
large enclosure should be provided. As with most tortoises, outdoor arrangements
are preferable to indoor setups if the climate is appropriate. A secure hiding
spot or area that allows burrowing is essential. In the wild these tortoises
often utilize burrows or excavate hollows in which to rest. Another vital
element is a water hole in which the tortoises can soak. These chelonians prefer
a more humid, moist environment than might be expected and will suffer if kept
too dry. Keepers should vary the amount of heat and direct light; species from
forested regions, such as K. homeana, generally prefer more shade than
grassland species. However, individual tortoises may differ, so experiment with
conditions to determine the specific tortoise's optimal environment.
Hinge-backs are omnivorous feeders in the wild. In addition to greens, they
consume snails, insects such as millipedes and beetles, and will scavenge
corpses when encountered. In captivity they will eat a wide variety of vegetable
matter, including green beans, broccoli, squash, mushrooms, and bananas. They
readily take mealworms and mealworm beetles, cooked chicken, and liver.
Earthworms are relished; they are grabbed, whipped from side to side, and
swallowed rapidly. As mentioned above, fresh water for drinking and soaking is
essential for a Hinge-back's health.
Although Hinge-backs are often available on dealer price lists and in pet
shops at a fairly low price, they are not an ideal tortoise for beginners.
Virtually all of these tortoises have been removed from their native habitat in
Africa and shipped to the United States. They often arrive in a stressed
condition, with no information available as to their place of origin. They
require a complete veterinary examination as soon after purchase as possible.
Determining an appropriate environment for the tortoise can be a daunting task
also. Many turtle-keepers report instances of Hinge-backs appearing to thrive
for a few months (or more) in captivity, but then suddenly declining. These
deaths may be due to a number of factors, such as an undiagnosed parasitic
infection or failure to provide some necessary component of the tortoise's diet
or environment. For beginning tortoise keepers, a much wiser investment would be
a captive-born Redfoot, Leopard, or African Spurred Tortoise (Geochelone
carbonaria, G. pardalis, or G. sulcata, respectively).
Experienced tortoise keepers with the desire to work with Kinixys
should attempt to establish viable breeding colonies. A large number of
Hinge-backs currently enter the United States pet market, even though they are
listed as a CITES II animal, because their native countries allow a high level
of export. This high level of trade cannot continue indefinitely without
depleting the wild populations. The breeding successes of tortoise keepers
within the native range of the various Kinixys species indicate that it
is possible to keep these chelonians in captivity. As a further example, three
European zoos successfully produced captive-born Hinge-backs (listed in the 1994
edition of Frank Slavens' Reptiles and Amphibians in Captivity: Breeding,
Longevity and Inventory), demonstrating that breeding is possible outside of
their native range. Outdoor maintenance and duplication of their native
environment may increase the chances of successful breeding in the United
States. Hopefully, captive-born individuals will prove much hardier in captivity
than their wild-caught ancestors, as has happened with other reptiles.
Hinge-backs are unique among the tortoises of the world. Their carapacial
hinge is a fascinating adaptation, affording the turtle increased protection
from predators. Many details of the life history of Kinixys are still
unknown. Hopefully the current levels of export will not damage native
populations to the extent that these details will never be worked out. People
keeping Hinge-backs should make every effort to care for them as the valuable
creatures they are, and not as the cheap pets they currently appear to be.
Bibliography and Other Books to Consult:
Boycott, Richard C. and Ortwin Bourquin. 1988. The South African Tortoise
Book. Southern Book Publishers, Johannesburg, SA.
Ernst, Carl H. and Roger W. Barbour. 1989. Turtles of the World. Smithsonian
Press, Washington, DC.
Highfield, A. C. 1990. Keeping and Breeding Tortoises in Captivity. R & A
Publishing, Ltd., Avon, England.
Iverson, John B. 1992. A Revised Checklist with Distribution Maps of the
Turtles of the World. Privately published.
Obst, Fritz Jurgen. 1988. Turtles, Tortoises and Terrapins. St. Martin's
Press, New York.
Patterson, Rod. 1987. Reptiles of Southern Africa
Pritchard, Peter C. H. 1979. The Encyclopedia of Turtles. T.F.H.
Publications, Neptune City, NJ.
Slavens, Frank L. and Kate Slavens. 1994. Reptiles and Amphibians in
Captivity: Breeding, Longevity and Inventory. Slaveware Publishing, Seattle, WA.
This article copyright © 1998 by David T. Kirkpatrick.
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