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Giant tortoises of the Seychelles islands

The Indian Ocean supported two genera of giant tortoise until humans settled in the islands. The Cylindraspis tortoises of Mauritius, Reunion and rodrigeus are all extinct but some of the Masdagascar-Seychelles tortoises survived. These bleonged to the genus Aldabrachelys (or Dipsochelys). Despite its name the genus originated on Madagascar, not Aldabra. On Madagascar there were two species: A. abrupta and A. grandidieri, both became extinct around 1,000 years ago.

Over the past million years Madagascar giant tortoises were carried by the tides to the Seychelles islands, there giving rise to four closely related forms of tortoise. These may have been distinct speices, subspecies or races of the Aldabra giant tortoise A. gigantea (or D. dussumieri). These are described in more detial below. On other pages informaiton can be found on the conservation of the Seychelles tortoises and their reintroduction to the wild.

Aldabra giant tortoise - Aldabrachelys g. giantea or Dipsochelys dussumieri

Aldabra tortoiseThis species is often known as Geochelone gigantea orDipsochelys elephantina. It is naturally restricted to Aldabraatoll, and possibly the nearby atolls, although it has been introduced toseveral of the granitic Seychelles islands. Some 100,000 wild tortoiseslive on Aldabra.

It is a domed species adapted to grazing on the low grass and herbs of theatoll.

Seychelles giant tortoise - Aldabrachelys gigantea hololissa or Dipsochelys hololissa

Seychelles tortoiseThis species inhabited the granitic islands of the Seychellesgroup where it grazed the vegetation on the edges of marshes and streams.By 1840 it had disappeared from the wild and was assumed to be extinct.In 1997 8 captive survivors were recognised in Seychelles. Thesewere included in the NPTS Seychelles Giant Tortoise Conservation Project.Since then other survivors have been found in zoos elsewhere in theworld. Only 12 adults are known.

As a grazing species, it superficially resembles the Aldabran tortoise inits domed shape but is distinct on close examination.

Arnold's giant tortoise - Aldabrachelys gigantea arnoldi or Dipsochelys arnoldi

Arnold's tortoiseAlsoknown as the Seychelles saddle-backed tortoise. This species also inhabitedthe granitic Seychelles islands until 1840. Captive tortoises wererecognised in 1997 and were part of the NPTS Seychelles Giant TortoiseConservation Project. Only 18 adults are known.

This species is adapted to browsing, it has a flattened 'saddle-backed' shell and unique jaw and leg modifications to enable it to browse efficiently. The 'saddle-backed' shape is most developed in some Galapagos tortoises where it is involved in browsing and in ritual combats. Such combats are not known in Seychelles tortoises and the 'saddle-backed' shell is less extreme.

In additon to these three forms there is a fourth, known only from a single adult skeleton and a picked juvenile: Daudin's giant tortoise Aldabrachelys gigantea daudinii or Dipsochelys daudinii.

The different species were described in detail in the journal of the Freshwater Turtle and Tortoise Specialist Group - Chelonian Conservation Biology 3(1) in August 1998. The feeding behaviour of the tortoises is described in issue 3(3) of December 1999.