Chelonoidis is a genus of turtles in the tortoise family erected by Leopold Fitzinger in 1835.[2] They are found in South America and the Galápagos Islands, and formerly had a wide distribution in the West Indies.
The members of this genus on the Galápagos Islands are among the largest extant terrestrial chelonians. Giant members of the genus, such as Lutz's giant tortoise (C. lutzae) were also present in mainland South America and the West Indies during the Pleistocene.[3]
They were formerly assigned to Geochelone, but a 2006 genetic analysis indicated that they were actually most closely related to hingeback tortoises.[4] However, a more recent genetic analysis of mtDNA has found that they are actually most closely related to the lineage containing Centrochelys and Geochelone.[5] Their ancestors apparently floated across the Atlantic from Africa to South America in the Oligocene.[4] This crossing was made possible by their ability to float with their heads up and to survive up to six months without food or water.[4] Based on mtDNA analysis, the extant Chelonoidis members can be divided into two lineages, with one containing the red-footed tortoise (C. carbonarius) and yellow-footed tortoise (C. denticulatus), and the other containing the Chaco tortoise (C. chilensis) and the Galapagos tortoises (C. niger complex). The now-extinct West Indian radiation is thought to group with the Chaco and Galapagos tortoises but is significantly basal to both, and was a rather evolutionary distinct lineage, having diverged well before any of the modern species in the genus did and only 7 mya after the divergence of Chelonoidis from African tortoises.[6]
A 2021 study found that the extent of divergence among the species in the Galápagos and Bahamian Chelonoidis radiations may have been overestimated, and supported subsuming many of the species in both complexes to being subspecies of two parent species; C. alburyorum for the Bahamas and Turks and Caicos Islands, and C. niger for the Galápagos.[5]
The names of several species names in the genus have often been misspelled, beginning in the 1980s when Chelonoidis was elevated to genus and mistakenly treated as feminine, an error recognized and fixed in 2017.[2]
Presently, Chelonoidis are distributed throughout most of South America, as well as most of the Galápagos; the genus extended north into Central America during the Pleistocene and most of the West Indies up to the late Holocene. C. carbonarius and C. denticulatus are presently found on some of the Lesser Antillean islands, but the provenance of these individuals is unknown, and they could have been introduced by Amerindians during pre-Columbian times.