Taxonomy of Indian Ocean Giant Tortoises (Dipsochelys)

The genus Dipsochelys comprises giant tortoises from Aldabra, Seychelles, and Madagascar. This paper reviews the taxonomy of the genus, recognizing and redescribing six species: D. dussumieri (Aldabra), D. daudinii (Seychelles?), D. hololissa (Seychelles), D. arnoldi (Seychelles), D. abrupta (Madagascar), and D. grandidieri (Madagascar). The species are reliably distinguished by their osteology, their external features being variable. The nomenclature of the Aldabran species is confused; this paper recommends a strict application of the rules of nomenclature and the resurrection of D. dussumieri (Gray, 1831) in preference to the invalid Geochelone gigantea (Schweigger, 1812) or the junior synonym D. elephantina (Dumeril and Bibron, 1835). Phylogenetic relationships supported by a cladistic analysis of osteological features suggest that the Malagasy species share a common ancestry with two of the Seychelles forms (D. arnoldi and D. hololissa ), with the Alda bran D. dussumieri and the presumed Seychelles species D. daudinii forming a separate clade. This may support suggestions that the Aldabran population is descended from an undescribed extinct population from the Comoros rather than from Madagascar. Of the six species redescribed only three remain extant (D. dussumieri, D. hololissa, and D. arnoldi).

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