Sahelanthropus tchadensis is thought to be one of the oldest hominid species, dating back at least 7 million years. While only skull bones have been recovered, the size of the canines and location of the foramen magnum suggest that it belongs in the hominid clade. However, not all scientists agree as Sahelanthropus had a brain smaller than a modern chimpanzee and prominent brow ridges.
The discovery of Sahelanthropus brought in to question the theory that pre-humans evolved in savannah habitats in southeren Africa. Sahelanthropus inhabitated the forests of central Africa and was both aboreal and terrestrial.
Brunet, M. (n.d.). Two new Mio-Pliocene Chadian hominids enlighten Charles Darwin's 1871 prediction. Philosophical Transactions of the Royal Society B-Biological Sciences, 365(1556), 3315-3321.