Some early hominin species have not been definitively assigned to one of the established genera within Hominidae (Pongo, Gorilla, Pan, or Homo). This is often because the fossil evidence for these species—teeth, bone fragments, or other artifacts—is too limited or ambiguous to confidently resolve genus-level classification. Ardipithecus ramidus, Kenyanthropus platyops, and Orrorin tugenensis are examples of hominins whose genus placement remains debated among researchers.