C4 grasses, grazers, and fire as a natural resource available to Homo, led to the spread of open grasslands
C4 grasses are competitive in open grasslands, the C4 pathway of carbon fixation lets the grass grow faster, supporting grazers that maintain the open landscape. The spread of C4 grasses in the late Pliocene and Pleistocene occurs at the same time as the Homo lineage appears in the fossil record, and grazing animals also become more and more common. Fire as a natural resource was widely available at the end of the Pliocene from volcanoes around Lake Turkana, no need to learn to rub sticks against one another, use flint, or gather fire from lightning strikes, fire could be picked up from the ground, and used to burn down large areas of forest, providing the bipedal, upright, Australopithecines (adaptation originally from 3-4Ma for swimming) with a habitat that fit their needs, and allowing other species to hitch-hike on that ecological niche.
The horse and C4 grasses in co-evolution on the Danakil block
Equids in Africa shifted from C3-dominated to C4-dominated diet in conjunction with a global expansion of C4 biomass during the Late Miocene (Cerling et al. 1997, Bedaso, Z. K. 2013). The Chorora formation, a fault along the Somali continent at the Mid Ethiopian Rift, that formed as the Danakil block separated from the north-eastern part of the formation around 9 million years ago, shows a more mixed C3/C4 dietary strategy (Bernor et al. 2004) and increasingly C4-dominated diets are seen at the Adu-Asa Formation where the coastal grasslands on the Danakil block were at 6.5-5.2 Ma, and the Sagantole formation to where Danakil had rotated by 4.6-4.2 Ma. At Aramis and later on Hadar, the Danakil equid lineage had adapted as pure grazers. (White et al. 2009)
Synapses
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