Final answer:
The location where Sahelanthropus tchadensis was discovered is considered unusual as it was in Chad, West Africa, not the typical East African Rift zone where many early hominin fossils are found, and the age of the fossil suggests it lived around the diverging time of humans and chimpanzees.
Step-by-step explanation:
The unusual aspect about the location where Sahelanthropus tchadensis was found is that it was a surface find in Chad, West Africa, which notably is quite distant from the East African Rift where many other early hominin fossils have been discovered. The fossil, nicknamed “Toumai,” is significant because it has been dated to nearly seven million years ago, which is around the same time that molecular data suggests the divergence between the line leading to modern humans and modern chimpanzees. However, its mosaic of primitive and evolved characteristics has created uncertainty regarding its exact place in the human lineage, particularly since it is unclear if Sahelanthropus was bipedal, given the characteristics of its foramen magnum and other cranial features.