Final answer:
Sahelanthropus tchadensis is an ancient fossil whose classification as a hominin is debated due to its mixture of primitive and evolved features, and its precise relationship to modern humans is uncertain.
Step-by-step explanation:
Whether Sahelanthropus tchadensis would or would not be classified as a hominin is a matter of ongoing research and debate among paleoanthropologists. Discovered in 2001-2002, Sahelanthropus tchadensis is an ancient fossil that has been dated to nearly seven million years ago, overlapping with the estimated time of divergence between the lineages that would lead to modern humans and modern chimpanzees. Though it possesses a mix of primitive and evolved characteristics, its classification as a hominin is not clear-cut. The species demonstrates a small cranial capacity similar to that of modern chimpanzees and possesses a large brow ridge, with the position of the foramen magnum suggesting a non-bipedal posture. In contrast, other early hominins, such as Orrorin tugenensis, show clear morphological evidence of bipedalism, and hominins like Homo habilis feature increased brain size and tool-making capabilities, marking them more definitively within the Homo genus.