Order: Artiodactyla
Family: Bovidae
Subfamily: Antilotraginae(?)
Tribe: Antilotragini
Genus: Antilotragos
Species: A. pharmakeia
They're opportunistic omnivores and rather commonly eat carrion; as well as birds, small mammals, lizards, crustaceans, and amphibians in addition to various leaves, branches, and fruits.
Unicorns are commonly thought to cure/be immune to poison. In the case of A. pharmakeia, this is a result of the fact that they frequently eat highly toxic plants with no ill effects. However, this does make their flesh rather toxic in turn, and as such they have very few predators.
Unlike many species in the same family, A. pharmakeia does not form herds.

I don't have a common name, yet. In any case, they're in the same family as goats, cows, and antelope but have their own subfamily.