First Known Hominin Identification

The question asks to identify the earliest known species belonging to the hominin lineage, which includes modern humans and our extinct ancestors after the split from the chimpanzee lineage.

Analyzing Hominin Candidates

• Australopithecus afarensis: This species, famously represented by the "Lucy" fossil, lived approximately 3 to 4 million years ago. While an early hominin, it is not the earliest known.
• Homo habilis: Known as "handy man," this species lived about 2.4 to 1.4 million years ago. It represents an early member of the *Homo* genus but appeared much later than the earliest hominins.
• Ramapithecus sivalensis: Fossils dated between 12.5 and 8.5 million years ago were once thought to represent an early hominin. However, current scientific consensus classifies *Ramapithecus* as an ancestor of modern orangutans, not on the direct human line.
• Ardipithecus ramidus: This species, discovered in Ethiopia, lived around 4.4 million years ago. Fossils like "Ardi" provide significant evidence of its early hominin status, making it one of the oldest known hominins.

Conclusion

Comparing the known time ranges, Ardipithecus ramidus, dating back to 4.4 million years ago, represents the earliest known hominin among the choices provided.