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Tortoises (Testudinidae)

Tortoises

(Testudinidae)

Class Reptilia

Order Testudines

Suborder Cryptodira

Family Testudinidae


Thumbnail description
Terrestrial turtles with elephantine hind legs, flattened forelegs, and unwebbed toes

Size
Up to 55 in (140 cm) carapace length and 562 lb (255 kg)

Number of genera, species
12 genera; ca. 47 species

Habitat
Terrestrial ecosystems

Conservation status
Critically Endangered: 1 species; Endangered: 7 species; Vulnerable: 16 species

Distribution
All major land masses except Australia and Antarctica

Evolution and systematics

This family is most closely related to the pond, river, and wood turtles of the family Geoemydidae. It is well represented in the fossil record, with material dating back to the Eocene. No subfamilies are recognized.

Physical characteristics

These are small to very large terrestrial turtles with a high-domed shell in all but one species; columnar hind limbs, elephantine

in appearance; forelimbs somewhat flattened and armored with large scales; and short and unwebbed toes, each with two or fewer phalanges.

Distribution

Mainly tropical and subtropical in North and South America, Europe, Asia, and Africa, as well as numerous oceanic islands.

Habitat

Terrestrial, from deserts and grasslands to shrublands to the floors of primary forests.

Behavior

Tortoises often engage in male-to-male combat, usually involving shell ramming, and sometimes even biting of the extremities. Temperate species spend the winter underground either buried in the soil or in burrows they have constructed.

Feeding ecology and diet

Most species are herbivorous, eating grasses, fruits, flowers, seeds, or foliage, but a few species also eat animal matter (even carrion) opportunistically.

Reproductive biology

Courtship usually includes the male chasing the female, often head bobbing, biting at her extremities, and/or ramming

her shell with his. Eggs are brittle-shelled, spherical to elongate, typically measuring 1–2 in (3–6 cm) in greatest diameter. Clutch sizes are generally small, ranging from one to 51 eggs per clutch, and are generally related to female size. Multiple clutches in one season are produced by many species, although some females apparently do not reproduce every year. Incubation is typically 100–160 days and is reported to last as long as 18 months in one species. Although most species have not been studied, those that have exhibit temperature-dependent sex determination, with females produced at high incubation temperatures and males at low temperatures.

Conservation status

Sixteen species are listed as Vulnerable, seven as Endangered, and one as Critically Endangered on the IUCN Red List. Because of their terrestrial habits, tortoises are especially vulnerable to human exploitation for food, traditional medicine, and the pet trade. Island populations have been especially prone to extirpation. Habitat destruction also takes its toll, especially for species inhabiting forested environments. Most species are legally protected by local countries, but illegal harvesting continues in most locales.

Significance to humans

Eaten by local people on every continent within its range.

Species accounts

List of Species

South American yellow-footed tortoise
Galápagos tortoise
Desert tortoise
Pancake tortoise
Hermann's tortoise

South American yellow-footed tortoise

Geochelone denticulata

taxonomy

Testudo denticulata Linnaeus, 1766, Virginia. No subspecies are recognized.

other common names

English: Morrocoy amarillo, yellow-footed tortoise.

physical characteristics

This is a large tortoise (up to 10 in [26 cm] carapace length) with an elongate, high-domed shell with the twelfth marginal scutes fused to form a supracaudal scute, the fifth and sixth marginal scutes touching the second pleural scutes, no nuchal scute, no carapacial or plastral hinge, a divided gular scute that does not strongly project anteriorly and does not reach the entoplastron, a humeropectoral seam that does not cross the entoplastron, the external narial opening basically rounded, the premaxilla lacking a medial ridge, but the maxilla bearing one, an unflattened tail that lacks an enlarged terminal scale, five claws on the forefeet, the forelegs with large yellow or orange scales, and the carapace with the older scutes areas yellow or orange.

distribution

Atlantic versant of northern South America, including the Amazon River basin; southern populations may be disjunct.

habitat

Tropical evergreen and deciduous forests.

behavior

Males use stereotyped head movements to identify other males. If a turtle does not respond with head movements, the male sniffs its cloacal region, presumably to confirm the sex and species. A returned head response elicits combat, in which males ram one another even to the point of one overturning the other.

feeding ecology and diet

This species is mostly herbivorous, feeding on fallen fruit, succulent plants, grasses, and mushrooms, but also eating termites and carrion.

reproductive biology

This tortoise may mate throughout the year. During courtship the male pushes or rams the female's shell and bites at her limbs to immobilize her. He mounts the female's shell from the rear for copulation, during which time his head and neck are fully extended forward and downward, his mouth is open, and he may make clucklike vocalizations. The nesting season is very extended and it has been suggested that it might occur year-round. Multiple clutches are produced at intervals of about one to two months. Captive females have produced up to four clutches per year. The eggs are brittle-shelled but their shape varies from spherical to elongate and from 1.6 to 2.4 in (40 to 60 mm) in greatest length by 1.4 to 2.2 in (35 to 56 mm) in width. Egg mass may range from 1.4 to 4.0 oz (41 to 112 g), averaging about 2.5 oz (72 g). Clutch size ranges from one to 12 eggs, although clutches of four to six are most common. Incubation requires 128–152 days (mean 136). The effect of temperature on sex during development is not known.

conservation status

This species is listed as Vulnerable on the IUCN Red List. Forest cutting is increasingly affecting this species.

significance to humans

These tortoises are eaten regularly by local peoples and also are collected in low numbers for the pet trade.


Galápagos tortoise

Geochelone nigra

taxonomy

Testudo nigra Quoy and Gaimard, 1824, Hawaiian Islands (in error). Twelve subspecies are variably recognized, and the taxonomy of the various island populations is controversial.

other common names

Spanish: Tortuga galápago.

physical characteristics

This is a large tortoise (up to 51 in [130 cm] carapace length) with a uniform black, dark brown, or gray carapace that varies in shape from domed and rounded to saddle shaped. The twelfth marginal scutes are fused to form a supracaudal scute, the fifth and sixth marginal scutes touch the second pleural scutes, no nuchal scute is present, no carapacial or plastral hinge is present, the divided gular scute does not strongly project anteriorly, the humeropectoral seam does not cross the entoplastron, the external narial opening is basically rounded, the premaxilla lacks a medial ridge, but the maxilla bears one, the unflattened tail lacks an enlarged terminal scale, and five claws are present on the forefeet.

distribution

Occurs only on the Galápagos Islands off Ecuador.

habitat

Volcanic islands, from semiarid lowlands to moist uplands.

behavior

These tortoises are active by day, but sleep under vegetation or overhanging rocks at night. The females in some populations migrate from feeding areas to nesting areas with appropriate soil and sunlight. Combat and courtship behaviors are similar to those in the yellow-footed tortoise, although the males are even more vocal, generating deep basal roars. When approached by Darwin's finches, these tortoises stand erect and allow the finches to glean skin, ticks, and other ectoparasites from their bodies.

feeding ecology and diet

This species is almost totally herbivorous, feeding on grasses, forbs, cacti and other succulents, sedges, fruits, and even the leaves of bushes.

reproductive biology

Courtship and mating are known from December to August, but vary by island. Nesting has been observed from late June to December, although the season varies in length by island. Possibly as many as four clutches are laid each year. The female excavates a flask-shaped nest, 7–12 in (18–30 cm) deep, with her hind feet. The eggs are almost spherical, brittle-shelled, and measure 2.2–2.6 in (56–65 mm) in greatest diameter. Clutch size ranges from two to 19 eggs depending on the female's size and island, with clutches of six to 10 being most typical. Incubation may take 85 to more than 200 days.

conservation status

This species is listed as Vulnerable on the IUCN Red List, but one subspecies is listed as Extinct, two as Extinct in the Wild, four as Vulnerable, four as Endangered, and one as Critically Endangered. Predation by cats, rats, dogs, and pigs and competition from goats, donkeys, and pigs all remain as problems.

significance to humans

This species is probably only rarely eaten by locals today, and perhaps their primary current significance is as an attraction for ecotourists.


Desert tortoise

Gopherus agassizii

taxonomy

Xerobates agassizii Cooper, 1863, southern California mountains, near Fort Mojave. No subspecies are recognized.

other common names

Spanish: Tortuga del desierto, tortuga de los cerros, tortuga del monte.

physical characteristics

This is a medium-sized tortoise (up to 19 in [49 cm] carapace length) with no plastral or carapacial hinge, a domed shell, the twelfth marginal scutes fused into a single supracaudal scute, the fifth vertebral scute the broadest in the series, the carapacial scutes with light centers, a single axillary scute on each bridge, a divided gular scute that does not strongly project anteriorly, the premaxilla and the paired maxilla each bearing a medial ridge, the forelimbs flattened and shovel-like, the width of the forefeet and hind feet approximately equal, and the tail not flattened.

distribution

Southwestern United States and northwestern Mexico.

habitat

Thorn scrub to cactus deserts.

behavior

This species constructs a burrow for use as a retreat from predators and the weather. Burrows may be barely long enough to accommodate the tortoise or as long as 33 ft (10 m) in northern sites. These tortoises remain inactive during the hottest parts of the day in summer and migrate to deeper burrows to hibernate for the winter. Desert tortoises are surprisingly social and head-bob at one another whenever they meet. Male-to-male encounters begin with head-bobbing, but escalate into ramming contests using the gular projections on the anterior plastron. This combat is occasionally intense enough to result in the overturning of one of the males.

feeding ecology and diet

Desert tortoises are mainly herbivorous, feeding on various grasses, cacti and other succulents, and flowers.

reproductive biology

Maturity in desert tortoises is reached after 15 to 20 years. Courtship and mating are continuous from the spring to the autumn. The male follows the female, bobbing his head as he overtakes and circles her. He then bites at her head, forelimbs, or shell, and may even ram her with the gular projections on his plastron. Eventually if she is receptive and remains stationary, he moves behind her and mounts her shell for copulation. He produces hissing and grunting sounds while mounted. Nesting occurs mainly from May though July, with one to three clutches of two to 15 eggs (usually five or six) being laid each year. However, some females apparently skip reproduction in some years. The eggs are brittle-shelled, elliptical to nearly spherical, and average 1.6–1.8 in (40–45 mm) by 1.3–1.5 in (34–38 mm). Incubation in the field requires 90–120 days.

conservation status

This species is listed as Vulnerable on the IUCN Red List. Habitat destruction (for road or housing construction, agriculture, livestock grazing, and by off-road vehicle use) is increasingly affecting natural populations. In addition, tortoises in many populations are afflicted with upper respiratory tract disease, caused by a mycoplasmic bacterium.

significance to humans

These tortoises increasingly are collected illegally for the Asian food markets in larger western U.S. cities.


Pancake tortoise

Malacochersus tornieri

taxonomy

Testudo tornieri Siebenrock, 1903, Busisi, Tanzania. No subspecies are recognized.

other common names

English: African pancake tortoise.

physical characteristics

This is a small tortoise (up to 7 in [18 cm] carapace length) with no plastral or carapacial hinge, a very low, flexible shell with great reduction in bones (unique among all tortoises), and a nuchal scute present.

distribution

Kenya and Tanzania in East Africa.

habitat

Rock outcrops in savannas and scrublands.

behavior

These tortoises are well-adapted to their rocky habitat. They are amazingly adept climbers and, when disturbed, quickly enter rock crevices and wedge themselves in place using their claws and sturdy limbs. They also estivate under rocks during hot, dry weather. Pancake tortoises also are known to bask.

feeding ecology and diet

This species is herbivorous, feeding on grasses, succulents, and leaves.

reproductive biology

Courtship has been observed in captivity in January and February and consists of the male trailing the female, biting at her limbs, climbing on her back, and biting at her head. Mating has been recorded only in December in the field. Nesting in the wild apparently occurs in July or August. A single brittle-shelled, elongate egg (1.7–1.9 in [44–48 mm] by 1–1.1 in [26–28 mm]) is generally laid per clutch, although two are produced on occasion. Captives produce up to six clutches per year, but nesting in the wild is unknown. Incubation requires 113–221 days.

conservation status

This species is listed as Vulnerable on the IUCN Red List. Removal for the pet trade and habitat alteration for agriculture pose the greatest threats to this tortoise.

significance to humans

These tortoises have been heavily exploited for the pet trade.


Hermann's tortoise

Testudo hermanni

taxonomy

Testudo hermanni Gmelin, 1789, no type locality given. Two subspecies are recognized.

other common names

None known.

physical characteristics

This is a small tortoise (up to 10 in [26 cm] carapace length) with no plastral or carapacial hinge, a domed shell with the twelfth marginal scutes separate (i.e., not fused into a supracaudal scute), a long narrow nuchal scute present, no enlarged tubercles on the thigh, a large horny scale on the end of the tail, five claws (usually) on the forefoot, and five to 10 longitudinal rows of small scales on the anterior surface of the foreleg.

distribution

Southern Europe from southeastern France to eastern Turkey and Romania.

habitat

Dry habitats with dense vegetation, from scrublands to woodlands.

behavior

The males engage in combat during the breeding season, by ramming other males and/or by biting at their heads and legs. The species hibernates during the winter by burrowing underground.

feeding ecology and diet

These tortoises are primarily herbivorous, feeding on legumes, buttercups, grasses, and fruits from trees. They also occasionally eat earthworms, snails, slugs, insects, and carrion.

reproductive biology

Courtship and mating are apparently concentrated in the spring. Courting males chase the female, ramming her shell, biting at her head and legs, and finally mounting her shell from behind. While mounted, the male may make high-pitched squeaks. Flask-shaped nests 3 in (7–8 cm) deep are constructed in April to June. The clutch size ranges from two to 12 eggs and is related to female size, with small females in western populations having smaller clutches than the larger eastern females. Up to three clutches may be laid per season. The brittle-shelled eggs are usually elongate, measuring 1.1–1.6 in (28–40 mm) by 0.8–1.2 in (21–30 mm). Incubation takes 55 to 90 days. This species exhibits temperature-dependent sex determination, with females produced at high incubation temperatures and males at lower temperatures.

conservation status

This species is noted as Lower Risk/Near Threatened on the IUCN Red List, although the subspecies Testudo hermanni hermanni is categorized as Endangered. The numbers of this tortoise are declining due to habitat destruction, wildfires, predation by feral animals, and removal for the pet trade.

significance to humans

These tortoises were once heavily exploited for the pet trade, but this occurs much less frequently today.


Resources

Books

Ballasina, D., ed. Red Data Book on Mediterranean Chelonians. Bologna, Italy: Edagricole, 1995.

Pritchard, Peter C. H., and Pedro Trebbau. The Turtles of Venezuela. Athens, OH: Society for the Study of Amphibians and Reptiles; Oxford, OH, 1984.

Periodicals

Moll, D., and M. W. Klemens. "Ecological Characteristics of the Pancake Tortoise, Malacochersus tornieri, in Tanzania." Chelonian Conservation and Biology 2, no. 1 (1996): 26–35.

Pritchard, Peter C. H. "The Galápagos Tortoises: Nomenclatural and Survival Status." Chelonian Research Monographs 1 (1996): 1–85.

Wallis, I. Z., B. T. Henen, and K. A. Nagy. "Egg Size and Annual Egg Production by Female Desert Tortoises (Gopherus agassizii): The Importance of Food Abundance, Body Size, and Date of Egg Shelling." Journal of Herpetology 33, no. 3 (1999): 394–408.

John B. Iverson, PhD

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