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THE LEOPARD TORTOISE

21 November 2013

www.leopard.tvThere often is confusion about the terms turtle and tortoise. According to the Oxford Dictionary of British English, a tortoise is a slow-moving land-living reptile with a bony shell while its relative the turtle is a marine or freshwater reptile with a bony or leathery shell, and webbed toes. Both these names have their roots in the same Middle English names tortu or tortuce which were derived from the Old French word tortue and the Spanish word tortuga. To confuse matters more some turtles are known as tortoises in Australia.

The tortoises fall under the Phylum Chordata or vertebrate animals and are cousins of the crocodiles, lizards and snakes in the Class Reptilia. The tortoises are all members of the family Testudidae. They are shielded from predators by having a hard external shell that develops from their ribs and is still attached to them and their toes are never webbed. The legs are covered with large, hard tubercles and have claws as an additional protection. The upper and lower parts of the shell are joined by means of an epidermal bony bridge while the hard shell is covered by bony scales that are modified epidermal skin. The rigid shell prohibits breathing by changing the chest cavity and a tortoise either pulls air into the mouth cavity which is then pushed into the lungs with throat oscillations, or it contracts the abdominal muscles to increase the internal volume of the shell.

Female tortoises generally have a smaller tail than the males and the tail is dropped down whereas the longer tail of the male is usually pulled up and to the side of the shell. Males also have a concave lower shell or plastron to aid in mating. Tortoises and turtles existed on the Earth before the lizards, snakes and crocodiles and date back to some 215 million years ago when they lived in Eurasia and North America. Some 60 million years ago, and 5 million years after the extinction of the dinosaurs, a giant turtle, which was estimated to have been 2.5 m long, lived in Colombia. Fossil tortoises from Africa include several giant tortoises which probably became extinct as a primary food for early human hunter-gatherers. Tortoises have mean life-span of around 150 years which is more than in humans. The oldest known tortoise was called Tu’i Malila and it was presented as a gift by Captain Cook to the Tongan royal family shortly after its birth in 1777. It died on 19 May 1965 at the age of 188 years.

Tortoises are still being hunted mercilessly all over the world for food and in the Caribbean Region and Mexico the fat is being used as an ingredient for cosmetics. The shells form part of traditional Chinese medicines and in Japan it is powdered and mixed with herbs for medicinal uses. Tortoises also form part of many cultural items, such as the drachma coin of Aegina in Greece from 700 to 550 BC, Maldive coins of 1984, and coins of the Ukraine and Russian Federation. It also appears on the coat of arms of the Cayman Islands, the British Ocean Territory, the Seychelles, the Galapagos Islands, Seirijai in Lithuania, Hönow in Germany, Hoppegarten in Germany, Grünheide in Germany, Crottendorf in Germany and the 701st Airlift Squadron of the USA.

The smallest living tortoise is the speckled padloper tortoise Homopus signatus of South Africa which is only 8 cm long and occurs in sandy areas. The largest are the various leopard tortoises Stigmochelys pardalis which can weigh more than 40 kg and are 75 cm long in exceptional cases. Normally, however, leopard tortoises weigh 8 to 12 kg and are 30 to 45 cm long with the females being larger than the males. The species was first described by Gray in 1873 and occurs widely in Africa. The subspecies Sigmochelys pardalis pardalis occurs in the Waterberg and there are also two species of hinged tortoise and the Kalahari tent tortoise in the Waterberg.

The shell of a leopard tortoise varies greatly in shape, patterning and coloration and there is no shield over the neck. The well-developed legs have five claws on each front foot and four on each hind foot. Young leopard tortoises are pale yellow in colour with a large dark spot in the centre of each vertebral and costal (rib) scute and all the scutes have dark edges. This creates a spotted pattern that has led to the common name leopard tortoise. A scute is a horny scale and consists mainly of protein and keratin. Adult leopard tortoises largely become a dull brown.

As do most tortoises, the leopard tortoise is active by day and starts to feed in the morning after first basking in the sun because it is cold-blooded like all reptiles. It spends the night under thick vegetation or rock crevices where shallow scrapes may be dug that are used repeatedly. In cold weather leopard tortoises may be inactive for weeks on end. Each leopard tortoise has a range that can be larger than 80 ha, sometimes much larger. Growth is slow at first as the small tortoises feed poorly because they have to remain under cover to escape predation. Hatchlings may therefore also eat worms and insect larvae to balance their diet. The diet of adult leopard tortoises consists of a variety of vegetation and includes succulents, grass culms and grasses that grow on path edges or the grazing lawns of some antelopes. They also eat fungi such as mushrooms and the faeces of carnivores that contain bones as a source of calcium. Food is located by an excellent sense of smell.

Sexual maturity occurs at an age of ten years. Leopard tortoises have an extended breeding season with mating happening from September to April. Several clutches, each containing six to 18 hard-shelled eggs with a diameter of about 45 mm, are laid from October to May. The female uses her keen sense of smell to locate appropriate soil conditions for a nesting site and urinates to soften the ground before digging a hole of some 250 mm deep with her hind feet. The eggs are then covered carefully with soil by using the hind feet and the soil is patted down with the hind feet. Incubation is slow and can exceed a year but most of the eggs hatch in March and April when soaking rains soften the soil enough for the hatchlings to dig themselves free by excavating a tunnel with a slope of 45 degrees. A hatchling weighs around 35 g and uses an egg tooth to break the hard shell of the egg. An egg tooth is a hard, white protuberance on the jaw of the beak of an embryonic bird or reptile.

 

Reference:

Alexander, G and J Marais 2010. A guide to the reptiles of southern Africa, third impression. Cape Town: Struik Nature, pp 386 - 388.

article by: Prof J du P Bothma

 

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