The first person to suggest a close affinity to the doves was Johannes Theodor Reinhardt, whose opinions were then supported by Hugh Edwin Strickland and Alexander Gordon Melville.

These birds reached an impressive size as a result of isolation on islands free of predators, in accordance with Foster's rule.

[2] In 1848, a new species within the now defunct genus Didus, D. nazarenus, was named by Hugh Edwin Strickland and Alexander Gordon Melville.

[7] A suborder named in 1893 by Sharpe, Didi was defined as a group including only the massive birds, that were sister to Columbidae, from the Mascarene Islands of Mauritius, Réunion, and Rodrigues.

Illiger concluded that the dodo was related to ostriches and rheas, and so placed Inepti in the order Rasores, as the sister family to Gallinacei, Epollicati (a defunct group including Turnix and Syrrhaptes[8]), Columbini, and Crypturi.

[2] In 1842, Johannes Theodor Reinhardt proposed they were ground doves, based on studies of a dodo skull he had rediscovered in the royal Danish collection of Copenhagen.

[11] Many different affinities have historically been suggested for the dodo, including that it was a small ostrich, a rail, an albatross, or a vulture.

[12] Comparison of mitochondrial cytochrome b and 12S rRNA sequences isolated from a dodo tarsal and a Rodrigues solitaire femur supported their close relationship and their placement within the family of pigeons and doves Columbidae.

[19] Osteological and molecular data has since led to the dissolution of the family Raphidae, and the dodo and solitaire are now placed in the columbid subfamily Raphinae and tribe Raphini, along with their closest relatives.

In 2024, the new subtribe Raphina was created to include only the dodo and the solitaire, and the authors proposed the vernacular name ‘Mascarene giant ground doves’ for them.

[20][d][21] The "Réunion solitaire", long considered a third extinct didine bird, has turned out to be an ibis; it is now known as Threskiornis solitarius.

[23] The lack of mammalian herbivores competing for resources on these islands allowed the solitaire and the dodo to attain very large sizes.

It was estimated that the relatives of the two species moved to the island about 35 million years ago, when a land bridge between Nazareth (Rodrigues) or St. Brandon banks and Mauritius formed.

The pelvic elements were thicker than those of flighted pigeons to support the higher weight, and the pectoral region and the small wings were paedomorphic, meaning that they were underdeveloped and retained juvenile features.

The dodo shared several other traits with the Rodrigues solitaire, such as features of the skull, pelvis, and sternum, as well as their large size.

[29] Illustrations and written accounts of encounters with the dodo between its discovery and its extinction (1598–1662) are the primary evidence for its external appearance.

[39] The skull was 170 millimetres (6.7 in) long, flattened at the top with the fore and hind parts elevated into two bony ridges structured with cancellous.

Though some dodo bones have been found with healed fractures, it had weak pectoral muscles and more reduced wings in comparison.

Though some dodo bones have been found with healed fractures, it had weak pectoral muscles and more reduced wings in comparison with the Rodrigues solitaire.

Since Rodrigues receives less rainfall and has more seasonal variation than Mauritius, which would have affected the availability of resources on the island, the solitaire would have more reason to evolve aggressive territorial behaviour.

[47] The human population on Mauritius (an area of 1,860 km2 or 720 sq mi) never exceeded 50 people in the 17th century, but they introduced other animals, including dogs, pigs, cats, rats, and crab-eating macaques, which plundered dodo nests and competed for the limited food resources.

The authors also pointed out that because the last sighting before 1662 was in 1638, the dodo was probably already quite rare by the 1660s, and thus a disputed report from 1674 by an escaped slave cannot be dismissed out of hand.

Its disappearance coincided with the tortoise trade between 1730 and 1750, when traders burnt off vegetation, hunted solitaires, and released cats and pigs that preyed on eggs and chicks.

[53] In 1755, Joseph-François Charpentier de Cossigny attempted to obtain a live specimen, as he had been assured the Rodrigues solitaire still survived in remote areas of the island.

[53] When he visited Rodrigues to observe the 1761 transit of Venus, Alexandre Guy Pingré encountered no solitaires, although he had been assured that they survived.