Kenyanthropus platyops, that I would say is a descendant of Au. anamnesis, is often positioned as the ancestor of the Homo lineage. The idea that I blogged about the other day, that the host switch of Pthirus gorillae around 3.3 million years ago was the result of an interbreeding event, leading to a hybrid species, Paranthropus, means that Kenyanthropus platyops would be older than the interbreeding event.

The hypothesis that there was interbreeding between Au. afarensis and gorillae is derived from that there was a host switch of lice, specifically to pubic hair, and then that 15 percent of the human genome is closer to gorilla than chimpanzee, as well as that the morphology of Paranthropus is gorilla-like, with sagittal crests on the cranium. That then, would mean that the ancestors of humans had acquired genetic content from gorillae.

It is also possible that the gorilla genes are the result of incomplete lineage sorting (ILS) and that the host switch was not from sexual contact, or, that the sexual contact did not result in offspring and so on, so, hybridization is a hypothesis.

If Kenyanthropus platyops dates to 3.5 Ma, before the interbreeding event, then they would not be the ancestral species. The environment they inhabited, the Turkana lake, is also further from where gorillae ancestors would have lived, higher up in the mountains at the Ethiopian plateau (where Chororapithecus abisyncis fossils are deposited from), and a second wave of migration from Danakil "bumping into" gorillas in the mountains is more probable.

References

Insights into hominid evolution from the gorilla genome sequence (2012)