Neanderthals, Flores, Denisovans. (The latter supposedly had the same brain capacity of modern humans!)
Picts, Navajos, Hopi, Zuni, the Algonquins, the Iroquois, the Mound Builders, whoever built Cahokia, the Anasazis. The Guaranis of S. America.
Sentinel Island is one of the Andaman...