Final answer:
The distinct characteristic of Kenyanthropus platyops that separates it from Australopithecus is its cranial morphology, which includes a flatter face and smaller molar size. While limb structure, dietary habits, and geographic distribution are important, they do not define a genus as clearly as cranial features do.
Step-by-step explanation:
The characteristic of Kenyanthropus platyops that makes it a distinct genus from Australopithecus is primarily its cranial morphology. Kenyanthropus featured a flatter face and a smaller molar size in comparison to the Australopithecus species. In particular, the cranial features such as the flatness of the cheekbones and the shape of the skull distinguish Kenyanthropus as a separate genus. Aspects like limb structure, dietary habits, and geographic distribution may show variability within a genus and are not as definitive in classifying a distinct genus.
Australopithecus and Kenyanthropus, while both early hominids are differentiated by anatomical and morphological differences in the fossil record. The Australopithecus genus is divided into robust and gracile types, with robust types having features such as large teeth, jaws, and a sagittal crest for strong jaw muscles. In contrast, gracile types, and Kenyanthropus platyops in particular, showed smaller, lighter features with no sagittal crest, which suggests differences in dietary adaptations as well.