The Antosians were a Humanoid species that resided on Antos. They evolved long before Humanity.

Their homeworld was Antos IV in the Antos star system of the Alpha Quadrant. (ST reference: Star Charts)

They were discovered shortly before the Romulan War and were noted as being a peaceful race with no interest in the affairs outside their world. However, they maintained peaceful relations with their neighbors. The native Antosians discovered a special technique called Cellular metamorphosis allowing them to alter their shape. This technique was, however, a closely kept secret that they kept amongst themselves for centuries. They later shared this knowledge with Starfleet Captain Garth of Izar in order to save his life after he was badly burnt in an accident. (TOS episode & novelization: Whom Gods Destroy; FASA RPG module: The Federation)

By the 24th century, the Antosians had joined the Federation. (ST reference: Star Charts)