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

Abstract

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.

Phylogenetic and spatial distribution of evolutionary diversification, isolation, and threat in turtles and crocodilians (non-avian archosauromorphs)

“…Our phylogeny is robust overall, with monophyly of all families, subfamilies, and genera strongly supported. Of particular note is the continued weak support for relationships in the tortoise family Testudinidae (but see [ 50 ]), as well as broader uncertainty in higher-level relationships among and placement of Cheloniidae, Chelydridae, Emydidae, and Platysternidae [ 47 , 51 – 53 ].…”

Ancient mitogenomics elucidates diversity of extinct West Indian tortoises

“…The newly generated mitogenomes of Chelonoidis were merged with our previously used annotated alignment 34 for tortoises, with the exception that only one sequence per Cylindraspis species was included. This alignment also contained previously obtained data for a subfossil specimen of Chelonoidis alburyorum from Sawmill Sink, Great Abaco, Bahamas 19 .…”

A nomenclature for fossil and living turtles using phylogenetically defined clade names

“…Composition-The clade Geochelona is currently believe to consists of 49 extant species of tortoises, including the Galapagos tortoise complex (TTWG 2017), and a rich Cenozoic fossil record (e.g., Lapparent de Broin 2000Vlachos and Rabi 2018;Vlachos 2018;Georgalis et al in press). Cylindraspis is the most basal branching clade of Geochelona (Kehlmaier et al 2019). This recently extinct clade of Mascarene tortoises can delineate the crown following our explicit exception noted in "Methods and discussion" above.…”

“…Composition-An extremely rich fossil record that spans most of the Cenozoic documents the spread of testudinids from Asia across the globe (Lapparent de Broin 2000Holroyd and Parham 2003;Joyce et al 2016a;de la Fuente et al 2018;Vlachos and Rabi 2018;Kehlmaier et al 2019;Georgalis et al in press). At present, 65 extant species are recognized with a near-global distribution (TTWG 2017).…”