Final answer:
The claim that Sahelanthropus tchadensis had a smaller brain than a modern chimp is false; it had a cranial capacity similar to that of a modern chimp and a large brow ridge. The specimen exhibits a mix of primitive and evolved characteristics.
Step-by-step explanation:
The statement that Sahelanthropus tchadensis had a small braincase, smaller than that of a modern chimp with a sloping face and big brow ridges is false.
Although Sahelanthropus tchadensis did indeed have a small braincase with a cranial capacity of roughly 350 cubic centimeters, this is about equivalent to that of a modern chimpanzee, and not smaller. However, the fossil known as "Toumai" does exhibit a large brow ridge.
The characteristics of Sahelanthropus tchadensis, such as the cranial capacity, the large brow ridge, and the foramen magnum, suggest that it has both primitive and evolved traits compared to later human ancestors.