Final answer:
The earliest definite hominins include species from the genera Homo, Australopithecus, Paranthropus, and Ardipithecus, with Homo habilis known as one of the early members of the genus Homo and Ardipithecus as one of the earliest bipedal hominins.
Step-by-step explanation:
The collective name for the earliest definite hominins encompasses several species that can be considered the forebearers of modern humans. These include members of the genera Homo, Australopithecus, Paranthropus, and Ardipithecus. One of the early species in the genus Homo is Homo habilis, which lived from about 2.5 to 1.4 million years ago and is considered possibly ancestral to Homo erectus. Before Homo habilis, there were species like Ardipithecus ramidus and Ardipithecus kadabba, which date as far back as 5.6 million years ago. Significant for the study of human evolution, these hominins exhibited features such as bipedality and tool-making, which distinguish them from other primate ancestors. Other early hominins include Sahelanthropus and Orrorin, with bipedality evident in fossils like Ardipithecus, which is dated to the Pliocene Era. As the earliest ancestors in the human lineage, these hominins offer crucial insights into our evolutionary past and provide the basis for understanding the development of Homo sapiens.