Eastern Africa is a boon for mammal fossils, making it an ideal region to piece together ancient ecosystems over the past 7 million years. With their extensive database of both ancient and modern mammal communities, the researchers focused on three traits: diet, body size, and digestive strategy. For all of these traits, they found that the makeup of ancient herbivore communities differed significantly from those of today. This is key, as herbivores directly shape the structure of ecosystems in ways that impact a wide variety of animal and plant species.
“Large herbivores aren’t just passive parts of an ecosystem, we know that they can shape the landscape. They’re eating the plants, and the biggest ones are knocking down trees or trampling soils, which collectively influences vegetation structure, fire regimes, nutrient cycling, and impacts other organisms, including humans,” said Faith.
For example, modern African ecosystems are dominated by ruminants — relatives of cows and antelopes that have four compartments in their stomachs to thoroughly break down food. Non-ruminants equipped with simple stomachs are comparatively rare, with at most eight species coexisting in the same area today. Non-ruminants, including relatives of elephants, zebras, hippos, rhinos and pigs, are like digestive conveyor belts, said Faith. They eat larger quantities of plants to make up for their inefficient digestion. In contrast to the present-day pattern, eastern African fossil records document landscapes rich in non-ruminant communities, with dozens of species co-existing within the same area.
Fossil and modern communities were also vastly different in terms of body sizes. The fossil records document lots more megaherbivores than their modern counterparts. A steady decline of megaherbivores began 4.5 million years ago until they represented a more modern distribution 700,000 years ago.
What is the impact of these eating machines all living together in the same places, when it’s not the case today?
“These ancient herbivore communities were probably consuming far more vegetation, which means less fuel for wildfires. Because fire is an important part of modern ecosystems in Africa and favors grasslands over woodlands, it’s going to fundamentally alter how things are working at the level of entire ecosystems, starting with the plant communities,” adds John Rowan, co-author and postdoctoral researcher at the University of Massachusetts Amherst. “Paleontologists have been aware of that, but until now, no one’s really tried to measure just how different the past was compared to the present.” Paper. paywall – J. Tyler Faith, John Rowan, Andrew Du. Early hominins evolved within non-analog ecosystems. Proceedings of the National Academy of Sciences, 2019; 201909284 DOI: 10.1073/pnas.1909284116 More.
Most interesting. If that’s true, claims that our behavior stems from challenges faced by our ancestors may need to be scrutinized. Our ancestors may not have faced the same challenges.
Check out the competition: Eating fat, not meat, led to bigger human type brains, say researchers. Theories of the evolution of the human brain are a war of trivial explanations that no one dares admit are too trivial for what they purport to explain. It’s like blaming World War II on indigestion, only monstrously bigger.
Earlier discussion of the fat theory.
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