Ancient mitogenomics clarifies radiation of extinct Mascarene giant tortoises (Cylindraspis spp.)

The five extinct giant tortoises of the genus Cylindraspis belong to the most iconic species of the enigmatic fauna of the Mascarene Islands that went largely extinct after the discovery of the islands. To resolve the phylogeny and biogeography of Cylindraspis, we analysed a data set of 45 mitogenomes that includes all lineages of extant tortoises and eight near-complete sequences of all Mascarene species extracted from historic and subfossil material. Cylindraspis is an ancient lineage that diverged as early as the late Eocene. Diversification of Cylindraspis commenced in the mid-Oligocene, long before the formation of the Mascarene Islands. This rejects any notion suggesting that the group either arrived from nearby or distant continents over the course of the last millions of years or had even been translocated to the islands by humans. Instead, Cylindraspis likely originated on now submerged islands of the Réunion Hotspot and utilized these to island hop to reach the Mascarenes. The final diversification took place both before and after the arrival on the Mascarenes. With Cylindraspis a deeply divergent clade of tortoises became extinct that evolved long before the dodo or the Rodrigues solitaire, two other charismatic species of the lost Mascarene fauna.