New research shows that the oldest ape, known as Morotopithecus, was not living off fruit in a dense forest as earlier thought but was in grassy woodland and adapted to leaf-eating.Credit: Judith Engbers/ iStock/ Getty Images Plus
Two related studies published in Science provide new insights into ape and human evolution, undermining three long-held ideas around the topic.
One of the studies looks broadly at habitats associated with nine fossil ape study sites (six in Kenya and three in Uganda). The second study solely focuses on Moroto, Uganda. where researchers sought to understand the interaction of apes with their environment.
Their findings show that Africa had a variety of habitats in the Early Miocene (about 15-20 million years ago). Contrary to the earlier idea that the region was entirely forested, it turns out that Africa hosted a wide range of mixed, open habitats including wooded grasslands.
The studies also reveal that a class of grass known as C4- photosynthesizing grasses (like those found in today’s savannahs) were an important element of Early Miocene habitats, more than 10 million years earlier than previously thought, according to co-author, Rahab Kinyanjui, senior research scientist, Earth Sciences Department, National Museums of Kenya.
“We analysed fossil plants’ silica cells (phytoliths), which are extremely valuable in identifying and distinguishing grasses,” says Kinyanjui, also affiliated with the Max Planck Institute of Geoanthropology in Germany and the Human Origins Program at the Smithsonian Institution of Natural History in Washington D.C.
Kinyanjui maintains that understanding the evolution of hominoid history, and how they interacted with, exploited and adapted to their environments, helps scientists understand the evolution of hominins – the more direct or close linage of the Homo species.
The Moroto site, in Uganda, demonstrates that the oldest ape, known as Morotopithecus, was not living off fruit in a dense forest as earlier thought.
“Instead, it was in grassy woodland and adapted to leaf-eating,” Kieran McNulty of the Department of Anthropology, University of Minnesota told Nature Africa.
Evidence derived from carbon isotopes, the C4 and potential-C4 grasses, were abundant during that period. On the other hand, evidence derived from phytoliths show that specific types of C4 and potential-C4 grasses were present.
However, “none of these methods allow us to identify grasses to the species level, (but) only to the level that we know some were C4 grasses,” explains McNulty who co-authored the study. The findings show that these grasses led to open landscapes that drove skeletal adaptations in hominoids during the early Miocene. The C4 grasses are able to withstand drier conditions and high temperatures and survive better in direct sun as opposed to their shade loving C3 grass predecessors.
The researchers say the need to forage in the grassy woodlands drove hominoids to develop versatile musculoskeletal systems. It was thought previously that fruit foraging in canopied, dense forests caused these locomotor changes.
Hominoid dental patterns showed that they consumed leaves with lower water content, like drier stalks of C4 grasses, rather than eating juicer forest fruits, the study says.
“It was thought that the ability to distribute larger body mass across multiple supports may have allowed apes to access fruits growing at the ends of small tree branches,” he says, adding that while that may have been true, the teeth of Morotopithecus suggest that it was adapted for leaf-eating.
What this suggests is that Morotopithecus may have needed to access young leaves on upper branches during times of food scarcity.
This is because the Moroto paleoenvironment is shown to be more open rather than a closed forest, McNulty says.
The findings strengthen calls for looking again at the evolution of plants and animals.
These studies came out of a broader collaborative project on the evolution of early apes in eastern Africa, known as Research on Eastern African Catarrhine and Hominoid Evolution (REACHE).
It brought together multiple distinct research teams representing dozens of institutions. and aimed to better understand the circumstances in which the oldest apes evolved.
This project began in 2013. It took several years to compile the results, compare them across and within sites, interpret and integrate the information by different ecological proxies, and write the actual text of both studies. The studies were funded by the National Science Foundation.
