Reunion Gallinule

The Réunion swamphen, also known as the Réunion gallinule or oiseau bleu, is a hypothetical extinct species of rail that was endemic to the Mascarene island of Réunion. While only known from 17th- and 18th-century accounts by visitors to the island, it was scientifically named in 1848, based on the 1674 account by Sieur Dubois. A considerable literature was subsequently devoted to its possible affinities, with current researchers agreeing it was derived from the swamphen genus Porphyrio. It has been considered mysterious and enigmatic due to the lack of any physical evidence of its existence.

Source: Wikipedia