Genetically within the family of pigeons and doves, it was most closely related to the also extinct dodo of the nearby island Mauritius, the two forming the subfamily Raphinae.

[3] The bird was first scientifically named in 1789 as a species of dodo (Didus solitarius, based on Leguat's description) by the German naturalist Johann Friedrich Gmelin in the thirteenth edition of Systema Naturae.

[4] In 1786, subfossil Rodrigues solitaire bones encrusted in stalagmite were discovered in a cave and sent to the French naturalist Georges Cuvier in about 1830.

[5] The English naturalists Hugh Edwin Strickland and Alexander Gordon Melville suggested the common descent of the Rodrigues solitaire and the dodo in 1848.

Strickland recognised its generic distinction and named the new genus Pezophaps, from ancient Greek pezos (πεζός 'pedestrian') and phaps (φάψ 'pigeon').

[10] Study of skeletal features by the Newtons indicated that the solitaire was morphologically intermediate between the dodo and ordinary pigeons, but differed from them in its unique carpal knob.

[15][16][17] For many years the dodo and the Rodrigues solitaire were placed in a family of their own, the Raphidae (formerly Dididae), because their exact relationships with other pigeons were unresolved.

Comparison of mitochondrial cytochrome b and 12S rRNA sequences isolated from the femur of a Rodrigues solitaire and the tarsal of a dodo confirmed their close relationship and their placement within the Columbidae.

[24] The Nicobar and spotted green pigeon were placed at the base of a lineage leading to the Raphinae, which indicates the flightless raphines had ancestors that were able to fly, were semi-terrestrial, and inhabited islands.

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

[1] The Rodrigues solitaire shared traits with the dodo, its closest relative, such as size and features in the skull, pelvis, and sternum.

Their pelvic elements were thicker than those of flighted birds (to support their greater weight), and their pectoral region and wings were paedomorphic (underdeveloped, retaining juvenile features).

[4] Before fossils of the carpal knob were found, Strickland noted that the keel of the sternum of the Rodrigues solitaire was so well-developed as to almost indicate it had possessed the power of flight; however, since the humerus was very short he inferred that this was instead related to Leguat's claim that they used their wings for defence.

[33][15] Leguat's statements were confirmed by another description by Julien Tafforet, who wrote in 1726: The solitaire is a large bird, which weighs about forty or fifty pounds.

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.

[1] Some evidence, including their large size and the fact that tropical and frugivorous birds have slower growth rates, indicates that the Rodrigues solitaire may have had a protracted development period.

[32] The French economist Pierre-André d'Héguerty, writing about his time on the island around 1735, stated that a captive Rodrigues solitaire (which he described as having a melancholic appearance) would always walk in the same line until running out of space, and then return.

It has been suggested that the maximum size attained by the solitaire and the dodo was limited by the amount of crop milk they were able to produce for their young during early growth.

[33] Leguat described the stones in the following passage, mentioning that Rodrigues solitaires refused to feed in captivity: Tho' these Birds will sometimes very familiarly come up near enough to one, when we do not run after them, yet they will never grow Tame.

We find in the Gizzards of both Male and Female, a brown Stone, of the bigness of a Hen's Egg, 'tis somewhat rough, flat on one side and round on the other, heavy and hard.

[28]The clutch was described as consisting of a single egg; given the bird's large size, this led to proposals that the solitaire was K-selected, which means it produced a low number of altricial offspring, which required extensive parental care until maturity.

[28]The size difference between sexes has led to the suggestion that the Rodrigues solitaire was not monogamous as stated by Leguat, and that this deeply religious man attributed the trait to the bird for moral reasons.

The Danish zoologist Japetus Steenstrup noted that some Rodrigues solitaire remains bore traces of having been broken by a human or perhaps another large predator, to extract bone marrow.

[9] Writing in 1735, the French lieutenant Gennes de la Chancelière described the capture and consumption of two specimens as follows: Our men told of having seen goats and a large quantity of birds of different kinds: they brought, amongst others, two of which were bigger by a third than the largest turkey; they appeared, nevertheless to be still quite young, still having down on the neck and head; their wingtips were but sparsely feathered, without any proper tail.

The young ones that were brought had the head made more or less like the latter animal, but their feet were similar to those of turkeys, instead of that of the ostrich which is forked and cloven in the shape of a hind's foot.

However, it has been claimed that the French naval officer Bertrand-François Mahé de La Bourdonnais sent a "solitaire" to France from the nearby island of Réunion around 1740.

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

[14] In 1755, the French engineer 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.

[14] The French astronomer Alexandre Guy Pingré did not encounter any solitaires when he visited Rodrigues to observe the 1761 transit of Venus, although he had been assured they survived.

His friend, the French astronomer Pierre Charles Le Monnier named the constellation Turdus Solitarius after the bird to commemorate the journey.