West African black rhino
The rarest of the black rhino subspecies, the West African black rhinoceros, is now recognized by the ICUN as extinct. The species, Diceros bicornis longpipes, was once widespread in central Africa, but the population began a steep decline due to poaching. The rhino was listed as "critically endangered" in 2008, but a survey of the animal's last remaining habitat in northern Cameroon failed to find any sign of the rhinos, either a true sighting or even evidence of its presence, like feces or feeding signs. No West African black rhinos are known to be held in captivity.
The West African black rhino is a subspecies of the black rhino, but all rhinos are in trouble. Some things are looking up for Eastern black rhinos, however. Two babies were born to rhinos raised in captivity and then released into the wild in 2012. Their birth brings the population to 702, according to the BBC.
The video below, created by WWF's Black Rhino Expansion Project, shows the lengths we need to go to prevent the loss of other species: