Final answer:
The earliest fossil hominins discovered that are considered ancestors of humans belonged to the species like Ardipithecus, Sahelanthropus, and Orrorin, with Ardipithecus being particularly noteworthy. Alongside these, later species such as Australopithecus and members of the genus Homo, like Homo habilis and Homo erectus, contributed crucially to hominin evolution.
Step-by-step explanation:
The earliest fossil hominins that have been discovered and identified as being closely related to humans belonged to the species of Ardipithecus, Sahelanthropus, and Orrorin. Among these, Ardipithecus is particularly noteworthy due to its confirmed bipedalism and relatively old age. The younger species of Ardipithecus, namely Ardipithecus ramidus, dates back to about 4.4 million years ago. Two species of Ardipithecus have been discovered: A. ramidus and A. kadabba. A. kadabba is older, with specimens dating back to 5.6 million years ago. However, it is important to note that the true placement of these early hominin species in the human evolutionary tree is subject to ongoing research and debate.
The Australopithecus genus, which includes several species, is another significant early hominin group. Australopithecines are known for their upright walking, a milestone in human evolution. The emergence of the genus Homo, which includes Homo habilis and Homo erectus, marks further advancements such as larger brain size and tool use.