Resolution of the scientific name of the Giant Tortoise
(Photo courtesy of FotoNatura)
Ever since their discovery by Europeans, giant tortoises of the Indian Ocean have been at the centre of taxonomic debates. Two groups are generally recognized from this region: the genus Cylindraspis (extinct Mascarene Islands tortoises), and the genus Aldabrachelys from Seychelles-Aldabra-Madagascar region (of which the Aldabra giant tortoise is the only surviving species). During the last two decades, there has been growing confusion about which scientific name to apply to the giant tortoise that lives on Aldabra. During this period at least four generic names (Aldabrachelys, Dipsochelys, Geochelone and Testudo) and three epithets (dussumieri, elephantina and gigantea) have been used for this tortoise, in various combinations.
When a potentially new species is found, at least one specimen is taken to an institution where it is described by experts and assigned a unique Latin name. This specimen is referred to as the 'type specimen'; meaning that from then on, it is taken to be representative of all individuals of that species.
The Aldabra giant tortoise debate revolved around differences in opinion between taxonomists who disagreed about which type specimen 'belonged to' which name.It is easy to imagine that early explorers, from different countries, whovisited many places around the world, sometimes brought back specimens of the same species - but to different countries, where they were then described as different species, despite being the same one; or that collectors accidentally mis-labeled a few of their thousands of specimens.
When such uncertainty occurs, it is the 'golden rule' that the first-named type specimen becomes the 'correct' one. The problem with the Aldabra tortoise name was twofold: firstly, there was high uncertainty about the identity (andexistence) of the first-named specimen. Secondly, the genus, Testudo, allocated to the first specimen is now itself an 'illegal' name, since it is not considered valid anymore. This has also happened for the second commonly used name, Geochelone, which is also no longer available, since it refers to unrelated tortoises elsewhere.
To resolve the issue, a biologist, Jack Frazier, proposed in 2006 to stabilise the uncertainty, and assigned the name Aldabrachelys gigantea to a so-called 'neo-type' (=new type specimen). Since then, many biologists have agreed with Frazier's suggestion, while some have argued in favour of: 1) keeping the old name; or 2) using another new name, Dipsochelys. The case was brought before the International Commission on Zoological Nomenclature, the official body for all taxonomical matters in zoology. In the ensuing publication of opinions on the case, the overwhelming majority of scientists working on tortoises or tortoise ecology were in favour of stabilising the name as 'Aldabrachelys gigantea'. After several years and many published comments on the matter a vote was finally taken last month which fixed the name of the Aldabra giant tortoise as proposed by Dr Frazier to Aldabrachelys gigantea.
Such confusion concerning scientific names, especially of threatened species (the giant tortoise is listed as Vulnerable on the IUCN red list and on CITES Appendix II) does not facilitate science, conservation or protected species policy, either nationally or internationally. SIF, as the management authority of Aldabra, and responsible for the protection of the giant tortoise in its endemic habitat, is therefore very relieved that the issue has been resolved and will be using the correct name Aldabrachelys gigantea from here forth.