Moriori is an East Polynesian language once spoken in the Chatham Islands (Rekohu) about 650km East of New Zealand. It is closely related to Māori and both languages share several features not found in other Polynesian languages (Clark, 1994). This suggests a shared history, which is supported by Māori traditions.
Unfortunately, Moriori numbers were depleted by a Māori invasion in the 1820s. Language loss was quick, however, a small number of Moriori texts survived. Most of the Moriori population today has Māori and European ancestry. For further details see Clark (1994) and King (2000).
Additional details on Moriori are available at Te Ara – The Encyclopedia of New Zealand.
Clark, R. (1994). Moriori and Māori: The linguistic evidence. In Sutton, D. (Ed.). The origins of the first New Zealanders (pp. 123-135). Auckland, New Zealand: Auckland University Press.
King, M. (2000). Moriori: A people rediscovered. (Rev. ed.). Auckland, New Zealand: Viking.