Tortoises (Testudinidae)

(vertebrate zoology) A family of tortoises in the suborder Cryptodira; there are about 30 species found on all continents except Australia.

(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

Resources

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.

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.

[Article by: John B. Iverson, PhD]