4. Discussion
Our phylogenetic analysis analysis suggests that Dipsochelys shares a common ancestor with modern Malagasy tortoise species. This grouping of Dipsochelys with the Malagasy species has also been suggested on the basis of cranial osteology (Gerlach, 2001). Therefore, the colonization of Aldabra, the Seychelles, and possibly the Comoros likely occurred from Madagascar or in a stepwise fashion beginning in Madagascar, as suggested by Arnold (1979). Our tests of alternate phylogenies suggest that it is extremely unlikely that Dipsochelys colonized the western Indian Ocean from either Africa or India, the only other plausible sources.