Ancient DNA elucidates the lost world of western Indian Ocean giant tortoises and reveals a new extinct species from Madagascar.

Before humans arrived, giant tortoises occurred on many western Indian Ocean islands. We combined ancient DNA, phylogenetic, ancestral range, and molecular clock analyses with radiocarbon and paleogeographic evidence to decipher their diversity and biogeography. Using a mitogenomic time tree, we propose that the ancestor of the extinct Mascarene tortoises spread from Africa in the Eocene to now-sunken islands northeast of Madagascar. From these islands, the Mascarenes were repeatedly colonized. Another out-of-Africa dispersal (latest Eocene/Oligocene) produced on Madagascar giant, large, and small tortoise species. Two giant and one large species disappeared c. 1000 to 600 years ago, the latter described here as new to science using nuclear and mitochondrial DNA. From Madagascar, the Granitic Seychelles were colonized (Early Pliocene) and from there, repeatedly Aldabra (Late Pleistocene). The Granitic Seychelles populations were eradicated and later reintroduced from Aldabra. Our results underline that integrating ancient DNA data into a multi-evidence framework substantially enhances the knowledge of the past diversity of island faunas.

A new species of extinct Late Quaternary giant tortoise from Hispaniola.

Insular giant tortoise diversity has been depleted by Late Quaternary extinctions, but the taxonomic status of many extinct populations remains poorly understood due to limited available fossil or subfossil material, hindering our ability to reconstruct Quaternary island biotas and environments. Giant tortoises are absent from current-day insular Caribbean ecosystems, but tortoise remains from Quaternary deposits indicate the former widespread occurrence of these animals across the northern Caribbean. We report new Quaternary giant tortoise material from several cave sites in Pedernales Province, southern Dominican Republic, Hispaniola, representing at least seven individuals, which we describe as Chelonoidis marcanoi sp. nov. Although giant tortoise material was first reported from the Quaternary record of Hispaniola almost 35 years ago, tortoises are absent from most Quaternary deposits on the island, which has been studied extensively over the past century. The surprising abundance of giant tortoise remains in both vertical and horizontal caves in Hispaniola's semi-arid ecoregion may indicate that this species was adapted to open dry habitats and became restricted to a habitat refugium in southeastern Hispaniola following climatic-driven environmental change at the Pleistocene-Holocene boundary. Hispaniola's dry forest ecosystem may therefore have been shaped by giant tortoises for much of its evolutionary history.

First report of Plesiochelys etalloni and Tropidemys langii from the Late Jurassic of the UK and the palaeobiogeography of plesiochelyid turtles.

Plesiochelyidae is a clade of relatively large coastal marine turtles that inhabited the shallow epicontinental seas that covered western Europe during the Late Jurassic. Although the group has been reported from many deposits, the material is rarely identified at the species level. Here, we describe historical plesiochelyid material from the Kimmeridge Clay Formation of England and compare it with contemporaneous localities from the continent. An isolated basicranium is referred to the plesiochelyid Plesiochelys etalloni based notably on the presence of a fully ossified pila prootica. This specimen represents the largest individual known so far for this species and is characterized by remarkably robust features. It is, however, uncertain whether this represents an ontogenetic trend towards robustness in this species, some kind of specific variation (temporal, geographical or sexual), or an abnormal condition of this particular specimen. Four other specimens from the Kimmeridge Clay are referred to the plesiochelyid Tropidemys langii. This contradicts a recent study that failed to identify this species in this formation. This is the first time, to the best of our knowledge, that the presence of Plesiochelys etalloni and Tropidemys langii is confirmed outside the Swiss and French Jura Mountains. Our results indicate that some plesiochelyids had a wide palaeobiogeographic distribution during the Kimmeridgian.