The human pubic lice split from gorilla lice (Pthirus gorillae) 3.3 million years ago.^[1] Paranthropus could have been an intermediary in that host switch, if they had thicker gorilla-like hair where Pthirus gorillae could thrive, while Australopithecus had more chimpanzee-like hair that hosted Pediculus capitis, which split from Pediculus schaeffi (chimpanzee lice) about 5.5–6 million years ago.

The Paranthropus lineage, and the speciation event 6 Ma

Popadin et al showed last year (2017)^[2] that the gorilla lineage interbred with the ancestor of chimpanzees, paranthropus and humans, an event that caused the speciation of the three lineages.

This introgression is also seen as lineage sorting in humans and chimpanzees, where 15% of the gorilla genome is closer to chimpanzees, and another 15% of the gorilla genome is closer to humans.^[3]

References

1. Pair of lice lost or parasites regained: the evolutionary history of anthropoid primate lice

2. Mitochondrial pseudogenes suggest repeated inter-species hybridization in hominid evolution

3. Insights into hominid evolution from the gorilla genome sequence