Minotaurus (ミノタウロス Minotaurosu) is a rare and near-extinct species found on Earth. They reside on Monster Island under the protection of Android 17. In the anime there appears to only be one left, while in the manga there are still several.
The Minotaurus are extremely rare, bull-like creatures. Their extremely valuable horns held the key to an immortality elixir, and as a result, they were over-hunted into extinction.
Though it was stated by the alien poacher leader, that Minotaurus horns are valuable for money and can be possible to make immortality medicine. Though its quite possible there were many poachers from earth or from space that were capturing the Minotaurus to make them go very nearly extinct.
Minotaurus is derived from the mythical creature Asterion, also known as "Minotaur", which was the offspring of Minos's wife, Pasiphae, and the Cretan Bull, the former being orchestrated by Poseidon to fall in love with the latter as punishment to Minos for keeping the Cretan Bull instead of killing it. It was then kept in a labyrinth where it fed on any humans that got in its way.