Two Studies Push Upright Ape Origins in Africa Back by 10 Million Years
Anthropologists have long thought that our ape ancestors evolved an upright torso with a view to pick fruit in forests, but recent research suggests a life in open woodlands and a eating regimen that included leaves as an alternative drove apes’ upright stature. The finding pushes back the origin of upright apes and that of grassy woodlands from between 7 million and 10 million years ago to 21 million years ago.
Fruit generally grows on trees’ outer branches, and to succeed in it, large apes must distribute their weight on these branches, then reach out with their hands toward their prize. This is far easier if an ape is upright. If its back is horizontal, its hands and feet are generally underneath the body, making it much harder to maneuver inside picking range. That is how modern apes reach fruit, and, it’s been theorized, that’s why apes evolved to be upright.
But the brand new research, centered around a 21-million-year-old fossil ape called Morotopithecus, suggests this may not be the case. As an alternative, researchers think early apes ate leaves and lived in a seasonal woodland with a broken cover and open, grassy areas. The researchers suggest this landscape, as an alternative of fruit in closed cover forests, drove apes’ upright stature.
The outcomes are contained in two papers just published within the journal Science.
Excavations in northwest Kenya, a part of a project to document climate some 21 million years ago. (Courtesy Kevin Uno)
One study focuses on a 21-million-year-old site in eastern Uganda. There, a gaggle led by University of Michigan researchers together with scientists from Columbia Climate School’s Lamont-Doherty Earth Observatory and other institutions examined fossils present in a single stratigraphic layer, including fossils of Morotopithecus, the oldest clearly documented ape species. Also inside this layer were fossils of other mammals, ancient soils called paleosols, and tiny silica particles from plants called phytoliths. The researchers used these lines of evidence to recreate the environment of Morotopithecus.
They found that the plants living on this landscape lived through alternating seasonal periods of rain and aridity. This also signifies that no less than a part of the yr, apes needed to depend on something aside from fruit to survive. Together, these findings indicate that Morotopithecus lived in an open woodland punctuated by broken cover forests composed of trees and shrubs.
“These open environments have been invoked to clarify human origins, and it was thought that you just began to get these more open, seasonal environments between 10 and seven million years ago,” said lead creator Laura MacLatchy of the University of Michigan. It was thought that our ancestors stared striding around on two legs since the trees were further apart. “Now that we’ve shown that such environments were present no less than 10 million years before bipedalism evolved, we want to actually rethink human origins, too,” said MacLatchy.
The primary clue that these ancient apes were eating leaves was within the apes’ molars, which had quite a few peaks and valleys. Molars like this are used for tearing fibrous leaves apart, while molars used for eating fruit are typically more rounded.
The researchers also examined the apes’ dental enamel, in addition to the dental enamel of other mammals present in the identical layer. They found that isotopic ratios—the abundance of two isotopes of the identical element—of their dental enamel showed that the apes and other mammals had been eating so-called C3 plants, that are more common in open woodland or grassy woodland environments today. C3 plants are primarily woody shrubs and trees adapted to arid conditions, while so-called C4 plants are arid-adapted grasses.
Previously, researchers believed equatorial Africa around 20 million years ago was thickly carpeted with forest, and that open seasonal woodlands and grasslands evolved only later. But the second paper, led by scientists at Baylor University, used a set of environmental proxies to reconstruct the vegetation structure from nine fossil ape sites across Africa, including the eastern Uganda site. These proxies revealed that C4 grasses were in every single place through the earlier time period. That means that these landscapes were all open, not forested.
“The isotope data from the traditional plant waxes and phytoliths collected from the Morotopithecus site provide strong evidence for C4 grasses on the landscape on the local scale,” said Kevin Uno, a paleoclimatologist at Lamont-Doherty and coauthor of each papers. “Other regional plant wax records from marine cores indicate little to no C4 grass in eastern African at the moment. So these recent data are exciting because we now have a recent puzzle to determine: Why can we see different signals on the local versus regional scale?”
To reconstruct the traditional environment at each location, the researchers used carbon isotope analyses of ancient soil organic matter, plant wax biomarkers and phytoliths found at each site. The carbon isotope analyses revealed that a wide selection of plants lived within the grasslands, starting from people who comprise closed cover to wooded grasslands.
Uno’s group at Lamont analyzed the wax biomarkers—substances left over from the waxy material that protects leaves. These indicated a big number of shrubs and trees in addition to grasses. Phytoliths—microscopic biosilica bodies that give plants their structure in addition to a defense against being eaten—provided further evidence for abundant C4 grasses, pushing back the oldest evidence of C4 grass-dominated habitats in Africa, and globally, by greater than 10 million years.
“The findings have transformed what we thought we knew about early apes, and the origin for where, when and why they navigate through the trees and on the bottom in multiple alternative ways,” said Robin Bernstein, program director for biological anthropology on the National Science Foundation, which sponsored the research.
Adapted from a press release by the University of Michigan.
