At least three species from the human family Homo may have lived together in Africa almost two million years ago, new research has suggested.
One of them, Homo erectus, is thought to be the most likely direct ancestor of people living today.
The others most probably came to an evolutionary dead end, experts believe.
Between 2007 and 2009, three new fossils were unearthed from a site near Lake Turkana in Kenya - known as the "cradle of mankind". They included a face, a near-complete lower jaw, and part of a second lower jaw.
Combined with a mysterious fossil known as "1470" found nearby four decades ago, they confirm the existence of a human species with a large brain case and long, flat face.
The fossils appear to be distinct both from Homo erectus and Homo habilis, another primitive species from the same era.
Before the new discoveries, experts had tentatively named the 1470 species Homo rudolfensis.
Dr Meave Leakey, co-leader of the Koobi Fora Research Project (KFRP) in Kenya, one of the scientists whose findings are published in the journal Nature, said: "For the past 40 years we have looked long and hard in the vast expanse of sediments around Lake Turkana for fossils that confirm the unique features of 1470's face and show us what its teeth and lower jaw would have looked like.
"At last we have some answers."
Co-author Professor Fred Spoor, from University College London, said: "Combined, the three new fossils give a much clearer picture of what 1470 looked like. As a result, it is now clear that two species of early Homo lived alongside Homo erectus. The new fossils will greatly help in unravelling how our branch of human evolution first emerged and flourished almost two million years ago."