Abstract:
Savannas first began to spread across Africa during the Miocene. A major hypothesis for
explaining this vegetation change is the increase in C4 grasses, promoting fire. We
investigated whether mammals could also have contributed to savanna expansion by using
spinescence as a marker of mammal herbivory. Looking at the present distribution of 1,852
tree species, we established that spinescence is mainly associated with two functional types of mammals: large browsers and medium-sized mixed feeders. Using a dated phylogeny for
the same tree species, we found that spinescence evolved at least 55 times. The
diversification of spiny plants occurred long after the evolution of Afrotherian
proboscideans and hyracoids. However, it is remarkably congruent with diversification of
bovids, the lineage including the antelope that predominantly browse these plants today.
Our findings suggest that herbivore-adapted savannas evolved several million years before
fire-maintained savannas and probably, in different environmental conditions. Spiny
savannas with abundant mammal herbivores occur in drier climates and on nutrient-rich
soils, whereas fire-maintained savannas occur in wetter climates on nutrient-poor soils.
