Arnold's giant tortoise

Arnold's giant tortoise
Scientific classification
Kingdom:	Animalia
Phylum:	Chordata
Class:	Sauropsida
Order:	Testudines
Suborder:	Cryptodira
Family:	Testudinidae
Genus:	Aldabrachelys
Species:	A. arnoldi
Binomial name
Aldabrachelys arnoldi Bour, 1982

Arnold's giant tortoise (Aldabrachelys arnoldi), also known as the Seychelles saddle-backed tortoise, inhabited the granitic Seychelles islands until around 1840, when it was presumed to be extinct, along with the Seychelles giant tortoise; a species which shared the same islands.

The report of oddly-shaped of tortoises in captivity in the mid-1990s prompted the Nature Protection Trust of Seychelles to investigate the identity of these captive tortoises. Examination of museum specimens of the 'extinct' Seychelles and Arnold species seemed to confirm some living tortoises do show characteristics of the supposedly extinct species. However, some recently published scientific papers on the genetics of the Seychelles and Indian Ocean tortoises provide conflicting results. Some studies suggest only one species was ever present in the islands, whilst others suggest three distinct, but closely related species.

These different views derive from studies of different genes. A synthesis of all available genetic data indicates Arnold's tortoise is genetically the most distinctive Dipsochelys tortoise. This fits with the ecology and morphology of the species, as a highly distinctive tortoise adapted to feeding on low vegetation rather than the grazing habits of the Seychelles giant tortoise and Aldabra giant tortoise. Due to its unusual 'saddlebacked' shape, this is the only Seychelles tortoise species that regularly basks in the sun. The other species will do so occasionally, but Arnold's tortoises rapidly lose heat from the skin of their exposed necks and need to heat up in the sun in the mornings.

A captive breeding program was established in 1997, and in December 2006, the five adult tortoises were returned to the wild on Silhouette Island, forming the first wild population of this species since the early 19th century.

References

• Jeremy J. Austin, E. Nicholas Arnaud & Roger Bour (2003). "Was there a second adaptive radiation of giant tortoises in the Indian Ocean? Using mitochondrial DNA to investigate speciation and biogeography of Aldabrachelys (Reptilia,Testudinidae)" (abstract page). Molecular Ecology 12: 1415–1424. doi:10.1046/j.1365-294X.2003.01842.x. PMID 12755871. http://www.blackwell-synergy.com/doi/abs/10.1046/j.1365-294X.2003.01842.x. 
• Eric P. Palkovacs, Monique Marschner, Claudio Ciofi, Justin Gerlach & Adalgisa Caccone (2003). "Are the native giant tortoises from the Seychelles really extinct? A genetic perspective based on mtDNA and microsatellite data" (abstract page). Molecular Ecology 12: 1403–1413. doi:10.1046/j.1365-294X.2003.01834.x. PMID 12755870. http://www.blackwell-synergy.com/doi/abs/10.1046/j.1365-294X.2003.01834.x. 
• Gerlach, J. & Bour, R. 2003 "Morphology of hatchling giant tortoises" Radiata 12; 11-12
• Gerlach, J. 2004 Giant Tortoises of the Indian Ocean. Chimiara publishers, Frankfurt
• Gerlach, J. 2005 "Interpreting morphological and molecular data on Indian Ocean giant tortoises" In: Huber, B.A. et al. (Eds.) African Biodiversity: Morphology, Molecules and Systematics Springer, New York
• Gerlach, J. 2004 "Effects of diet on the systematic utility of the tortoise carapace" African Journal of Herpetology 53(1): 77-85.
• Gerlach, J. 2005 "Thermoregulation in captive Indian Ocean giant tortoises" Chelonian Conservation & Biology 4; 937-941

External links

• 'Extinct' Giant Tortoises Rediscovered, islandbiodiversity.com

• Release of Arnold’s giant tortoises Dipsochelys arnoldi on Silhouette island, Seychelles