Final answer:
Sahelanthropus tchadensis, a hominin dating to nearly seven million years ago, was discovered in Chad, and its mix of primitive and advanced features adds to our understanding of human evolution.
Step-by-step explanation:
The important localities of Sahelanthropus tchadensis relate to its discovery and the implications it has on our understanding of human evolution. The only known specimen of Sahelanthropus, a skull known informally as "Toumai," was discovered in Chad, Central Africa, in 2001-2002. This species is notable for its age, dating to nearly seven million years ago, which places it around the time that the ancestral lines to modern humans and chimpanzees are believed to have diverged based on molecular data.
Sahelanthropus tchadensis displays a mix of primitive and advanced features. With a cranial capacity similar to that of a chimpanzee, at 350 cubic centimeters, and a large brow ridge, Sahelanthropus does not fit neatly into the known lineage leading to Homo sapiens. Furthermore, the positioning of the foramen magnum suggests that Sahelanthropus was likely not bipedal, a critical feature in human evolution.