The horse evolutionary lineage also maps to the counter-clockwise rotation of Danakil^[1], descendant from Miocene "forest horses"^[2] and filled a niche as a grazer on the "open grasslands" of the south-western coast-line, together with Paranthropus (P. deyiremeda, 3.5 Ma)^[3] who also ate grass and was descendant from "forest gorillas" and a hybrid between gorilla and ardipithecus.^[4]

Paranthropus as a knuckle-walker

Based on the idea the idea that Paranthropus descended from forest-apes in the same way that Hipparion affarensis descended from forest-horses, and data that points to that Paranthropus ate grass^[5], and so displayed parallel evolution with horses, they may have been knuckle-walkers, making it easier to graze along the coast of Danakil.

References

1. Strong clockwise block rotation of the Ali-Sabieh/Aïsha Block: evidence for opening of the Afar Depression by a ‘saloon-door’ mechanism (2015)

2. The evolution and paleodiet of the Eurygnathohippus feibeli lineage in Africa (2013)

3. New species from Ethiopia further expands Middle Pliocene hominin diversity (2015)

4. Mitochondrial pseudogenes suggest repeated inter-species hybridization in hominid evolution (2017)

5. Diet of Paranthropus boisei in the early Pleistocene of East Africa (2011)

6. Evidence that humans evolved from a knuckle-walking ancestor (2000)