Chemical analysis of East African fossils and ancient soil samples from 21 million years ago show that hominoids were eating drier leaves as opposed to juicy fruits, and probably were not restricted to the canopies of trees as has long been thought.
Two related studies reveal that savannah grasses emerged in East Africa more than 10 million years earlier than previously thought. This challenges the longstanding palaeoecological theory that almost all of East Africa was covered in dense forest 21 million years ago.
WATCH: New Australian palaeo book illustrated by hand
It has long been theorised that a drying climate which saw the reduction of East Africa’s forests in favour of grassy woodland and savannah, drove skeletal adaptations in hominoids toward bipedalism – an essential biomechanical step on the road to becoming human.
Walking upright on two legs allowed early ancestors of humans to see over long grass and freed up their hands for the development of tools, accelerating human evolution.
Now, it appears that this transformation began taking place in the early Miocene between 21 million and 17 million years ago.
A paper published in Science reveals that ancient soil samples from nine sites in what is now Kenya and Uganda, bear high chemical signatures of plants that have evolved to withstand drier and hotter conditions.
The biochemical signature shows an abundance in that time period of grasses that photosynthesise via the C4 carbon fixation pathway.
Carbon fixation refers to the process by which carbon dioxide is used to synthesise sugars such as glucose. C4 plants transform CO2 into a four-carbon molecule as the first step in producing sugar. C3 plants first transform CO2 into a three-carbon molecule.
C4 grasses withstand direct sunlight better than their C3 predecessors which prefer shadier environments.
Past research indicated that C4 grasses appeared in East Africa, heralding the transformation of dense jungle into open plains, less than 10 million years ago. The new research pushes their emergence back over 10 million years.
Read more: Why do humans like to get ‘high’? Our ape cousins may hold the evolutionary clue
Another paper published in Science analysed the dental and skeletal fossils of Morotopithecus – an ancient ape that lived in Uganda 21 million years ago during the early Miocene. The study allowed researchers to determine what the animals were eating.
Dental patterns showed the apes were eating leaves with lower water content, such as the drier stalks of C4 grasses, rather than juicier forest fruits.
Skeletal structure, including femurs, vertebrae and torso of the prehistoric apes, also resembled those of modern non-human primates that inhabit savannahs and other open ecosystems today.
Do you care about the oceans? Are you interested in scientific developments that affect them? Then our new email newsletter Ultramarine, launching soon, is for you. Click here to become an inaugural subscriber.
Originally published by Cosmos as East African grassy woodlands which propelled evolution of bipedalism in human ancestors emerged 10 million years earlier than thought
Evrim Yazgin has a Bachelor of Science majoring in mathematical physics and a Master of Science in physics, both from the University of Melbourne.
Read science facts, not fiction...
There’s never been a more important time to explain the facts, cherish evidence-based knowledge and to showcase the latest scientific, technological and engineering breakthroughs. Cosmos is published by The Royal Institution of Australia, a charity dedicated to connecting people with the world of science. Financial contributions, however big or small, help us provide access to trusted science information at a time when the world needs it most. Please support us by making a donation or purchasing a subscription today.