Arnold's Giant Tortoise
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| Dipsochelys arnoldi |
Arnold's Giant Tortoise (Dipsochelys arnoldi) also known as the Seychelles saddle-backed tortoise inhabited the granitic Seychelles islands until around 1840. At that time 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 that 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 that 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 that Arnold's tortoise is genetically the most distinctive Dipsochleys 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 occasionally but Arnold's tortoises rapidly loose heat form the skin of their exposed necks and need to heat up in the sun in the mornings.
A captive breeding programme 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 1800s (see report).
[edit] Source
Austin, J.A., Arnold, E.N. & Bour, R. 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). Molecular Ecology (2003) 12, 1415–1424. © 2003 Blackwell Publishing Ltd
Palkovacs, E.P., Marschner, M., Ciofi, C., Gerlach, J. & Caccone, A. 2003. Are the native giant tortoises from the Seychelles really extinct? A genetic perspective based on mtDNA and microsatellite data. Molecular Ecology (2003)12, 1403–1413. © 2003 Blackwell Publishing Ltd
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
