page_title: Spotted green pigeon
section_title: Evolution
hierarchical_section_title: Spotted green pigeon / Taxonomy / Evolution
caption_attribution_description: Skeleton cast and model of dodo at the Oxford University Museum of Natural History, based on modern research.[1]
context_page_description: The spotted green pigeon or Liverpool pigeon is a species of pigeon which is most likely extinct. It was first mentioned and described in 1783 by John Latham, who had seen two specimens of unknown provenance and a drawing depicting the bird. The taxonomic relationships of the bird were long obscure, and early writers suggested many different possibilities, though the idea that it was related to the Nicobar pigeon prevailed, and it was therefore placed in the same genus, Caloenas. Today, the species is only known from a specimen kept in World Museum, Liverpool. Overlooked for much of the 20th century, it was recognised as a valid extinct species by the IUCN Red List only in 2008. It may have been native to an island somewhere in the South Pacific Ocean or the Indian Ocean, and it has been suggested that a bird referred to as titi by Tahitian islanders was this bird. In 2014, a genetic study confirmed it as a distinct species related to the Nicobar pigeon, and showed that the two were the closest relatives of the extinct dodo and Rodrigues solitaire.
  The surviving specimen is 32 cm long, and has very dark, brownish plumage with a green gloss.
context_section_description: In 2014, an ancient DNA analysis by the Australian geneticist Tim H. Heupink and colleagues compared the genes of the only spotted green pigeon specimen with that of other pigeons, based on samples extracted from two of its feathers. One of the resulting phylogenetic trees (or cladograms) is shown below:
  The spotted green pigeon was shown to be closest to the Nicobar pigeon. The genetic distance between the two was more than is seen within other pigeon species, but similar to the distance between different species within the same genus. This confirmed that the two were distinct species in the same genus, and that the spotted green pigeon was a unique, extinct taxon. The genus Caloenas was placed in a wider clade in which most members showed a mixture of arboreal (tree-dwelling) and terrestrial (ground-dwelling) traits. That Caloenas was placed in such a morphologically diverse clade may explain why many different relationships have previously been proposed for the members of the genus. A third species in the genus Caloenas, the Kanaka pigeon (C. canacorum), is only known from subfossils discovered in New Caledonia and Tonga. This species was larger than the two other members of the genus, so it is unlikely that it represents the same species as the spotted green pigeon. The possibility that the spotted green pigeon was a hybrid between other species can also be disregarded based on the genetic results.
  The distribution of the Nicobar pigeon and the Kanaka pigeon (which does not appear to have had diminished flight abilities) suggests dispersal through island hopping and an origin for the spotted green pigeon in Oceania or southeast Asia. The fact that the closest relatives of Caloenas were the extinct subfamily Raphinae (first demonstrated in a 2002 study), which consists of the dodo from Mauritius and the Rodrigues solitaire from Rodrigues, indicates that the spotted green pigeon could also have originated somewhere in the Indian Ocean. In any case, it seems most likely that the bird inhabited an island location, like its relatives. That the Caloenas pigeons were grouped in a clade at the base of the lineage leading to Raphinae indicates that the ancestors of the flightless dodo and Rodrigues solitaire were able to fly, and reached the Mascarene Islands by island hopping from south Asia.
caption: Raphines, such as the dodo, are the closest relatives of the genus Caloenas.
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