Final answer:
Sahelanthropus tchadensis shows a mix of primitive and evolved traits with a small cranial capacity, prominent brow ridge, and features suggesting bipedalism, living around the time when humans and chimpanzees diverged.
Step-by-step explanation:
The characteristics of Sahelanthropus tchadensis, an early hominin species discovered in Chad, suggest it lived around 7 million years ago (MYA), which aligns with the estimated divergence time between humans and chimpanzees. This species possessed a mix of primitive and evolved traits. One of the hallmark features is a relatively small cranial capacity of approximately 350 cubic centimeters (cc), akin to that of a chimpanzee, in contrast to the 1,400 cc typically found in modern humans. Additionally, Sahelanthropus tchadensis had a prominent brow ridge and the placement of the foramen magnum indicated that it was likely not bipedal, suggesting its head was positioned differently than in modern humans who walk upright.
Other characteristics include small jaws and teeth, and a third molar relatively larger than other molars, traits also observed in australopithecines and some early Homo species. However, the skull shape bore a resemblance to later hominins like H. erectus or H. habilis. It's important to note that these aspects make it difficult to determine Sahelanthropus tchadensis's specific place in the evolutionary lineage leading to modern humans, and its classification as a direct ancestor remains uncertain.