Tortoise

Tortoises (/ˈtɔːr.təs.ɪz/) are reptile species of the family Testudinidae of the order Testudines (the turtles). They are particularly distinguished from other turtles by being land-dwelling, while many (though not all) other turtle species are at least partly aquatic. Like other turtles, tortoises have a shell to protect from predation and other threats. The shell in tortoises is generally hard, and like other members of the suborder Cryptodira, they retract their necks and heads directly backwards into the shell to protect them.

For other uses, see Tortoise (disambiguation).

Tortoises
Temporal range: Paleocene–Recent
Aldabra giant tortoise
(Aldabrachelys gigantea)
Scientific classification
Kingdom: Animalia
Phylum: Chordata
Class: Reptilia
Order: Testudines
Suborder: Cryptodira
Superfamily: Testudinoidea
Family: Testudinidae
Batsch, 1788
Type species
Testudo graeca

Tortoises are unique among vertebrates in that the pectoral and pelvic girdles are inside the ribcage rather than outside. Tortoises can vary in dimension from a few centimeters to two meters. They are usually diurnal animals with tendencies to be crepuscular depending on the ambient temperatures. They are generally reclusive animals. Tortoises are the longest-living land animals in the world, although the longest-living species of tortoise is a matter of debate. Galápagos tortoises are noted to live over 150 years, but an Aldabra giant tortoise named Adwaita may have lived an estimated 255 years. In general, most tortoise species can live 80–150 years.

Terminology

Differences exist in usage of the common terms turtle, tortoise, and terrapin, depending on the variety of English being used; usage is inconsistent and contradictory.[1] These terms are common names and do not reflect precise biological or taxonomic distinctions.[2]

Tile with two rabbits, two snakes, and a tortoise, illustration for Zakariya al-Qazwini's book, Iran, 19th century

The American Society of Ichthyologists and Herpetologists uses "turtle" to describe all species of the order Testudines, regardless of whether they are land-dwelling or sea-dwelling, and uses "tortoise" as a more specific term for slow-moving terrestrial species.[1] General American usage agrees; turtle is often a general term (although some restrict it to aquatic turtles); tortoise is used only in reference to terrestrial turtles or, more narrowly, only those members of Testudinidae, the family of modern land tortoises; and terrapin may refer to turtles that are small and live in fresh and brackish water, in particular the diamondback terrapin (Malaclemys terrapin).[3][4][5][6] In America, for example, the members of the genus Terrapene dwell on land, yet are referred to as box turtles rather than tortoises.[2]

British usage, by contrast, tends not to use "turtle" as a generic term for all members of the order, and also applies the term "tortoises" broadly to all land-dwelling members of the order Testudines, regardless of whether they are actually members of the family Testudinidae.[6] In Britain, terrapin is used to refer to a larger group of semiaquatic turtles than the restricted meaning in America.[4][7]

Australian usage is different from both American and British usage.[6] Land tortoises are not native to Australia, yet traditionally freshwater turtles have been called "tortoises" in Australia.[8] Some Australian experts disapprove of this usage—believing that the term tortoises is "better confined to purely terrestrial animals with very different habits and needs, none of which are found in this country"—and promote the use of the term "freshwater turtle" to describe Australia's primarily aquatic members of the order Testudines because it avoids misleading use of the word "tortoise" and also is a useful distinction from marine turtles.[8]

Biology

Lifecycle
Adult male leopard tortoise, South Africa
Young African sulcata tortoise

Most species of tortoises lay small clutch sizes, seldom exceeding 20 eggs, and many species have clutch sizes of only 1–2 eggs. Incubation is characteristically long in most species, the average incubation period are between 100 and 160 days. Egg-laying typically occurs at night, after which the mother tortoise covers her clutch with sand, soil, and organic material. The eggs are left unattended, and depending on the species, take from 60 to 120 days to incubate.[9] The size of the egg depends on the size of the mother and can be estimated by examining the width of the cloacal opening between the carapace and plastron. The plastron of a female tortoise often has a noticeable V-shaped notch below the tail which facilitates passing the eggs. Upon completion of the incubation period, a fully formed hatchling uses an egg tooth to break out of its shell. It digs to the surface of the nest and begins a life of survival on its own. They are hatched with an embryonic egg sac which serves as a source of nutrition for the first three to seven days until they have the strength and mobility to find food. Juvenile tortoises often require a different balance of nutrients than adults, so may eat foods which a more mature tortoise would not. For example, the young of a strictly herbivorous species commonly will consume worms or insect larvae for additional protein.

The number of concentric rings on the carapace, much like the cross-section of a tree, can sometimes give a clue to how old the animal is, but, since the growth depends highly on the accessibility of food and water, a tortoise that has access to plenty of forage (or is regularly fed by its owner) with no seasonal variation will have no noticeable rings. Moreover, some tortoises grow more than one ring per season, and in some others, due to wear, some rings are no longer visible.[10]

Tortoises generally have one of the longest lifespans of any animal, and some individuals are known to have lived longer than 150 years.[11] Because of this, they symbolize longevity in some cultures, such as China. The oldest tortoise ever recorded, and one of the oldest individual animals ever recorded, was Tu'i Malila, which was presented to the Tongan royal family by the British explorer James Cook shortly after its birth in 1777. Tu'i Malila remained in the care of the Tongan royal family until its death by natural causes on May 19, 1965, at the age of 188.[12] The record for the longest-lived vertebrate is exceeded only by one other, a koi named Hanako, whose death on July 17, 1977, ended a 226-year lifespan.[13]

The Alipore Zoo in India was the home to Adwaita, which zoo officials claimed was the oldest living animal until its death on March 23, 2006. Adwaita (also spelled Addwaita) was an Aldabra giant tortoise brought to India by Lord Wellesley, who handed it over to the Alipur Zoological Gardens in 1875 when the zoo was set up. West Bengal officials said records showed Adwaita was at least 150 years old, but other evidence pointed to 250. Adwaita was said to be the pet of Robert Clive.[14]

Harriet was a resident at the Australia Zoo in Queensland from 1987 to her death in 2006; she was believed to have been brought to England by Charles Darwin aboard the Beagle and then on to Australia by John Clements Wickham.[15] Harriet died on June 23, 2006, just shy of her 176th birthday.

Timothy, a female spur-thighed tortoise, lived to be about 165 years old. For 38 years, she was carried as a mascot aboard various ships in Britain's Royal Navy. Then in 1892, at age 53, she retired to the grounds of Powderham Castle in Devon. Up to the time of her death in 2004, she was believed to be the United Kingdom's oldest resident.[16]

Jonathan, a Seychelles giant tortoise living on the island of St Helena, may be as old as 188 years [17] or 184 years.[18]

Sexual dimorphism

Many species of tortoises are sexually dimorphic, though the differences between males and females vary from species to species.[19] In some species, males have a longer, more protruding neck plate than their female counterparts, while in others, the claws are longer on the females.

The male plastron is curved inwards to aid reproduction. The easiest way to determine the sex of a tortoise is to look at the tail. The females, as a general rule, have smaller tails, dropped down, whereas the males have much longer tails which are usually pulled up and to the side of the rear shell.

Brain

The brain of a tortoise is extremely small. Red-footed tortoises, from Central and South America, do not have an area in the brain called the hippocampus, which relates to emotion, learning, memory and spatial navigation. Studies have shown that red-footed tortoises may rely on an area of the brain called the medial cortex for emotional actions, an area that humans use for actions such as decision making.[20]

In the 17th century, Francesco Redi performed an experiment that involved removing the brain of a land tortoise, which then proceeded to live six months. Freshwater tortoises, when subjected to the same experiment, continued similarly, but did not live so long. Redi also cut the head off a tortoise entirely, and it lived for 23 days.[21][22][23]

Distribution

Tortoises are found from southern North America to southern South America, around the Mediterranean basin, across Eurasia to Southeast Asia, in sub-Saharan Africa, Madagascar, and some Pacific islands. They are absent from Australasia [24] They live in diverse habitats, including deserts, arid grasslands, and scrub to wet evergreen forests, and from sea level to mountains. Most species, however, occupy semiarid habitats.

Diet
Baby tortoise feeding on lettuce
Tortoise feeding on a cactus

Most land-based tortoises are herbivores, feeding on grasses, weeds, leafy greens, flowers, and some fruits, although some omnivorous species are in this family. Pet tortoises typically require diets based on wild grasses, weeds, leafy greens and certain flowers. Certain species consume worms or insects and carrion in their normal habitats. Too much protein is detrimental in herbivorous species, and has been associated with shell deformities and other medical problems. Different tortoise species vary greatly in their nutritional requirements.

Taxonomy

This species list largely follows Turtle Taxonomy Working Group (2019)[25] and the Turtle Extinctions Working Group (2015)[26]

Skeleton of a tortoise
A skeleton of Aldabra giant tortoise found in Cousin Island (Seychelles).
Fossil of the extinct Ergilemys insolitus
Achilemys cassouleti, the most primitive testudine

Family Testudinidae Batsch 1788[27]

  • †Alatochelon[28]
    • † Alatochelon myrteum
  • Aldabrachelys Loveridge and Williams 1957:166[29]
  • Astrochelys Gray, 1873:4[30]
    • Astrochelys radiata, radiated tortoise
    • Astrochelys yniphora, angonoka tortoise, (Madagascan) plowshare tortoise
  • Centrochelys Gray 1872:5[31]
  • Chelonoidis Fitzinger 1835:112[32]
    • † Chelonoidis alburyorum Abaco tortoise, Late Pleistocene, extinct circa 550 BC
    • Chelonoidis carbonaria, red-footed tortoise
    • Chelonoidis chilensis, Chaco tortoise, Argentine tortoise or southern wood tortoise
    • † Chelonoidis cubensis
    • Chelonoidis denticulata, Brazilian giant tortoise, yellow-footed tortoise
    • † Chelonoidis lutzae Lutz's giant tortoise, Late Pleistocene
    • † Chelonoidis monensis
    • Chelonoidis nigra complex:[33]
      • † Chelonoidis abingdonii, Pinta Island giant tortoise, Abingdon Island giant tortoise (extinct)
      • Chelonoidis becki, Wolf Volcano giant tortoise, Cape Berkeley giant tortoise
      • Chelonoidis chathamensis, San Cristobal giant tortoise, Chatham Island giant tortoise
      • Chelonoidis darwini, San Salvador giant tortoise, James Island giant tortoise
      • Chelonoidis duncanensis, Pinzon giant tortoise, Duncan Island giant tortoise
      • Chelonoidis hoodensis, Espanola giant tortoise, Hood Island giant tortoise
      • † Chelonoidis nigra, Floreana giant tortoise, Charles Island giant tortoise (extinct)
      • Chelonoidis phantastica, Fernandina giant tortoise, Narborough Island giant tortoise
      • Chelonoidis porteri, Santa Cruz giant tortoise, Indefatigable Island giant tortoise
      • Chelonoidis vicina, Isabela Island giant tortoise, Albemarle Island giant tortoise
    • † Chelonoidis sellovii Southern Cone giant tortoise, Pleistocene
    • † Chelonoidis sombrerensis Sombrero giant tortoise, Late Pleistocene
  • Chersina Gray 1830:5
  • † Cheirogaster Bergounioux 1935:78
    • †Cheirogaster gymnesica Late Pliocene to Early Pleistocene
    • †Cheirogaster schafferi Pliocene to Early Pleistocene
  • Chersobius Fitzinger, 1835
  • †Cylindraspis Fitzinger 1835:112[32] (all species extinct) following Austin and Arnold, 2001:[34]
  • Geochelone Fitzinger 1835:112[32]
    • † Geochelone burchardi Tenerife giant tortoise[35]
    • † Geochelone vulcanica Gran Canaria giant tortoise[36]
    • Geochelone elegans, Indian star tortoise
    • Geochelone platynota, Burmese star tortoise
    • † Geochelone robusta Malta giant tortoise
  • Gopherus Rafinesque 1832:64[37]
  • † Hadrianus
    • Hadrianus corsoni (syn. H. octonarius)
    • Hadrianus robustus
    • Hadrianus schucherti
    • Hadrianus utahensis
  • † Hesperotestudo
    • Hesperotestudo alleni
    • Hesperotestudo angusticeps
    • Hesperotestudo brontops
    • Hesperotestudo equicomes
    • Hesperotestudo impensa
    • Hesperotestudo incisa
    • Hesperotestudo johnstoni
    • Hesperotestudo kalganensis
    • Hesperotestudo niobrarensis
    • Hesperotestudo orthopygia
    • Hesperotestudo osborniana
    • Hesperotestudo percrassa
    • Hesperotestudo riggsi
    • Hesperotestudo tumidus
    • Hesperotestudo turgida
    • Hesperotestudo wilsoni
  • Homopus Duméril and Bibron 1834:357[38]
  • Indotestudo Lindholm, 1929
    • Indotestudo elongata, elongated tortoise, yellow-headed tortoise
    • Indotestudo forstenii, Forsten's tortoise, East Indian tortoise
    • Indotestudo travancorica, Travancore tortoise
  • Kinixys
    • Kinixys belliana, Bell's hinge-back tortoise
    • Kinixys erosa, forest hinge-back tortoise, serrated hinge-back tortoise
    • Kinixys homeana, Home's hinge-back tortoise
    • Kinixys lobatsiana, Lobatse hinge-back tortoise
    • Kinixys natalensis, Natal hinge-back tortoise
    • Kinixys spekii, Speke's hinge-back tortoise
  • Malacochersus Lindholm 1929:285[39]
  • Manouria Gray 1854:133[40]
    • Manouria emys, Asian giant tortoise, brown tortoise (mountain tortoise)
    • Manouria impressa, impressed tortoise
  • † Megalochelys Falconer, H. and Cautley, P.T. 1837.[41]
    • † Megalochelys atlas, Atlas tortoise, Extinct – Pliocene to Pleistocene
    • † Megalochelys cautleyi, Cautley's giant tortoise
  • Psammobates Fitzinger 1835:113[32]
    • Psammobates geometricus, geometric tortoise
    • Psammobates oculifer, serrated tent tortoise, Kalahari tent tortoise
    • Psammobates tentorius, African tent tortoise
  • Pyxis Bell 1827:395[42]
  • Stigmochelys Gray, 1873
  • † Stylemys (Genus extinct)
    • Stylemys botti
    • Stylemys calaverensis
    • Stylemys canetotiana
    • Stylemys capax
    • Stylemys conspecta
    • Stylemys copei
    • Stylemys emiliae
    • Stylemys frizaciana
    • Stylemys karakolensis
    • Stylemys nebrascensis (syn. S. amphithorax)
    • Stylemys neglectus
    • Stylemys oregonensis
    • Stylemys pygmea
    • Stylemys uintensis
    • Stylemys undabuna
  • Agrionemys
  • Testudo

In religion
Bas-relief from Angkor Wat, Cambodia, shows Samudra manthan-Vishnu in the centre, his turtle Avatar Kurma below, asuras and devas to left and right

In Hinduism, Kurma (Sanskrit: कुर्म) was the second Avatar of Vishnu. Like the Matsya Avatara, Kurma also belongs to the Satya Yuga. Vishnu took the form of a half-man, half-tortoise, the lower half being a tortoise. He is normally shown as having four arms. He sat on the bottom of the ocean after the Great Flood. A mountain was placed on his back by the other gods so they could churn the sea and find the ancient treasures of the Vedic peoples.

In Judaism and early Christianity tortoises were seen as unclean animals .[43]

Tortoise shells were used by ancient Chinese as oracle bones to make predictions.

The tortoise is a symbol of the Ancient Greek god, Hermes.

See also World Turtle and Cultural depictions of turtles.

  • Baby Testudo marginata emerges from its egg
  • Baby tortoise, less than a day old
  • Testudo graeca ibera, Testudo hermanni boettgeri, Testudo hermanni hermanni, Testudo marginata sarda
  • Young (3.5 years) African spurred tortoise, Geochelone sulcata
  • Young, 20-year-old Tanzanian leopard tortoise feeding on grass
  • Aldabra giant tortoise, Geochelone gigantea
  • 22-year-old leopard tortoise
  • African spurred tortoise from the Oakland Zoo
  • Pair of African spurred tortoises mate in a zoo
  • Boy rides a tortoise at a zoo
  • Young Testudo hermanni
gollark: Do you *need* that?
gollark: Maybe this "unidict" thing.
gollark: We definitely need NC and all the FPS-enhancing mods.
gollark: Well, obviously.
gollark: Eeeh.

See also

References
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  2. Burton, Maurice and Burton, Robert (2002). International Wildlife Encyclopedia. Marshall Cavendish. ISBN 0761472665. p. 2796.
  3. Orenstein, Ronald Isaac (2001). Turtles, Tortoises and Terrapins: Survivors in Armor. Firefly Books. ISBN 1770851194
  4. "Turtle". Sandiegozoo.org. Archived from the original on 2010-12-06. Retrieved 2012-09-16.
  5. What is the difference between turtles, terrapins, and tortoises? Archived 2015-05-05 at the Wayback Machine, North Carolina Aquariums (July 1997).
  6. Dawkins, Richard (2009). The Greatest Show on Earth: The Evidence for Evolution. Free Press. ISBN 1416594795. p. 174.
  7. Endangered Wildlife and Plants of the World, Vol. 1. Marshall Cavenish. (2001). ISBN 0761471952. p. 1476.
  8. Romanowski, Nick (2010). Wetland Habitats: A Practical Guide to Restoration and Management. CSIRO Publishing. ISBN 9780643096462. p. 134.
  9. Highfield, Andy. "Tortoise egg incubation". Tortoisetrust.org. Archived from the original on 2013-09-05. Retrieved 2009-04-07.
  10. Veterinary Services Department, Drs. Foster & Smith, Inc. "Shells: Anatomy and Diseases of Turtle and Tortoise Shells". Retrieved 2013-10-22.CS1 maint: multiple names: authors list (link)
  11. Moon, J. C.; McCoy, E. D.; Mushinsky, H. R.; Karl, S. A. (2006). "Multiple Paternity and Breeding System in the Gopher Tortoise, Gopherus polyphemus". Journal of Heredity. 97 (2): 150–157. doi:10.1093/jhered/esj017. PMID 16489146.
  12. "Tortoise Believed to Have Been Owned by Darwin Dies at 176". Associated Press via FOXNews. 2006-06-26. Archived from the original on July 1, 2006.CS1 maint: unfit url (link)
  13. Barton, Laura (2007-04-12). "Will You Still Feed Me..." The Guardian. London. Retrieved 2013-01-08.
  14. "'Clive of India's' tortoise dies". BBC News. 2006-03-23. Retrieved 2009-04-07.
  15. Thomson, S.; Irwin, S.; Irwin, T. (1995). "Harriet, the Galapagos tortoise: disclosing one and a half centuries of history". Intermontanus. 4 (5): 33–35.
  16. "Timmy the tortoise dies aged 160". 2004-04-07. Retrieved 2019-05-30.
  17. Meet Jonathan, St Helena's 182-year-old giant tortoise BBC, March 13, 2014
  18. Boer War memento puts years on Jonathan the tortoise. The Times, December 4, 2008
  19. "Sexing Your Tortoise". Tortoise Supply. Retrieved 13 February 2017.
  20. "Tortoises Show Off Smarts by Mastering Touch-Screen Tech". Live Science. Retrieved 2016-12-01.
  21. Cuvier, Georges; Smith, Charles Hamilton; Pidgeon, Edward (1831). The animal kingdom arranged in conformity with its organization. 9. Printed for G. B. Whittaker. pp. 54–.
  22. The London Literary Gazette and Journal of Belles Lettres, Arts, Sciences, Etc. H. Colburn. 1831. pp. 277–.
  23. Broderip, William John (1852). Leaves from the Note Book of a Naturalist. E. Littell & Company. p. 83 (left column). In the beginning of November he opened the skull of a land-tortoise, removed every particle of brain, and cleaned the cavity out... instead of dying or remaining motionless, it groped its way about....
  24. "Chelonoidis - an overview | ScienceDirect Topics". www.sciencedirect.com. Retrieved 2019-09-27.
  25. Rhodin, Anders G.J.; Inverson, John B.; Roger, Bour; Fritz, Uwe; Georges, Arthur; Shaffer, H. Bradley; van Dijk, Peter Paul (August 3, 2017). "Turtles of the world, 2017 update: Annotated checklist and atlas of taxonomy, synonymy, distribution, and conservation status(8th Ed.)" (PDF). Chelonian Research Monographs. 7. ISBN 978-1-5323-5026-9. Retrieved October 4, 2019.
  26. Rhodin, A.G.J.; Thomson, S.; Georgalis, G.; Karl, H.-V.; Danilov, I.G.; Takahashi, A.; de la Fuente, M.S.; Bourque, J.R.; Delfino M.; Bour, R.; Iverson, J.B.; Shaffer, H.B.; van Dijk, P.P.; et al. (Turtle Extinctions Working Group) (2015). "Turtles and tortoises of the world during the rise and global spread of humanity: first checklist and review of extinct Pleistocene and Holocene chelonians" (PDF). Chelonian Research Monographs. 5(8):000e.1–66. Chelonian Research Monographs. 5. doi:10.3854/crm.5.000e.fossil.checklist.v1.2015. ISBN 978-0965354097. Archived from the original (PDF) on 2019-07-18. Retrieved 2019-11-13.
  27. Batsch, A.J.G.C. (1788). Versuch einer Anleitung zur Kenntniss und Geschichte der Thiere und Mineralien. Erster Theil. Allgemeine Geschichte der Natur; besondre der Säugthiere, Vögel, Amphibien und Fische. Jena: Akademischen Buchandlung, 528 pp.
  28. Adán Pérez‐García; Evangelos Vlachos; Xabier Murelaga (2020). "A large testudinid with African affinities in the post‐Messinian (lower Pliocene) record of south‐eastern Spain". Palaeontology. 63. doi:10.1111/pala.12468.
  29. Loveridge, Arthur; Williams, Ernest E. (1957). "Revision of the African tortoises and turtles of the suborder Cryptodira". Bulletin of the Museum of Comparative Zoology. 115 (6): 163–557.
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  33. Testudinidae, The Reptile Database
  34. Austin, J. J.; Nicholas Arnold, E. (2001). "Ancient mitochondrial DNA and morphology elucidate an extinct island radiation of Indian Ocean giant tortoises (Cylindraspis)". Proceedings of the Royal Society B: Biological Sciences. 268 (1485): 2515–23. doi:10.1098/rspb.2001.1825. PMC 1088909. PMID 11749704.
  35. "The Recently Extinct Plants and Animals Database cubit: The Recently Extinct Plants and Animals Database Extinct Reptiles: Geochelone burchardi". cubits.org. Archived from the original on 2016-06-19. Retrieved 2016-06-17.
  36. "The Recently Extinct Plants and Animals Database cubit: The Recently Extinct Plants and Animals Database Extinct Reptiles: Geochelone vulcanica". cubits.org. Archived from the original on 2016-06-24. Retrieved 2016-06-17.
  37. Rafinesque, Constantine Samuel (1832). "Description of two new genera of soft shell turtles of North America". Atlantic Journal and Friend of Knowledge. 1: 64–65.
  38. Duméril, André Marie Constant and Bibron, Gab riel. 1834. Erpétologie Générale ou Histoire Naturelle Complète des Reptiles. Tome Premier. Paris: Roret, 439 pp.
  39. Lindholm, Wassili A. (1929). "Revidiertes Verzeichnis der Gattungen der rezenten Schildkröten nebst Notizen zur Nomenklatur einiger Arten". Zoologischer Anzeiger. 81: 275–295.
  40. Gray, John Edward (1834). "Characters of several new species of freshwater tortoises (Emys) from India and China". Proceedings of the Zoological Society of London. 2: 53–54.
  41. Falconer, H.; Cautley, P.T. (1837). "On additional fossil species of the order Quadrumana from the Siwalik Hills". Journal of the Asiatic Society of Bengal. 6: 354–360.
  42. Bell, T. (1827). "XVI. On two new Genera of Land Tortoises" (PDF). Transactions of the Linnean Society of London. 15 (2): 392–401. doi:10.1111/j.1095-8339.1826.tb00122.x. Archived from the original (PDF) on 2018-09-05. Retrieved 2015-08-28.
  43. Thomas, Richard. "TORTOISES AND THE EXOTIC ANIMAL TRADE IN BRITAIN FROM MEDIEVAL TO 'MODERN'" (PDF). Testudo. 8 – via British Chelonia Group site.

Further reading
  • Chambers, Paul (2004). A Sheltered Life: The Unexpected History of the Giant Tortoise. London: John Murray. ISBN 978-0-7195-6528-1.
  • Ernst, C. H.; Barbour, R. W. (1989). Turtles of the World. Washington, DC: Smithsonian Institution Press.
  • Gerlach, Justin (2004). Giant Tortoises of the Indian Ocean. Frankfurt: Chimiara.
  • Antoinette C. van der Kuyl; Donato L. Ph. Ballasina; John T. Dekker; Jolanda Maas; Ronald E. Willemsen; Jaap Goudsmit (February 2002). "Phylogenetic Relationships among the Species of the Genus Testudo (Testudines: Testudinidae) Inferred from Mitochondrial 12S rRNA Gene Sequences". Molecular Phylogenetics and Evolution. 22 (2): 174–183. doi:10.1006/mpev.2001.1052. ISSN 1055-7903. PMID 11820839.
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