Researchers propose that an upright body design in early primates helped them reach leafy foliage more efficiently than fruit, a conclusion echoed by studies from the University of Michigan.
For generations, many anthropologists believed that ancient apes and early human ancestors developed a mostly vertical posture to access fruit. The common picture showed fruits growing away from the trunk on thin branches, prompting a lean and an outstretched arm to grab the prey. This view highlighted great apes like chimpanzees, which can stand and operate on thicker branches, as key examples of a vertical shift in locomotion and feeding behavior.
Laura McLatchy and her team explored the idea further by examining Morotopithecus, an early ape dating to about 21 million years ago. Their work suggests that this species may have evolved leaf-based feeding as a diet strategy. The researchers analyzed fossilized remains from the Morotopithecus site, alongside the surrounding layer which preserved ancient soil and plant traces as well as other mammal remains. That combination allowed scientists to reconstruct an ecological picture of the time, showing how Morotopithecus lived within a landscape that featured open forests, frequent clearings, and dense shrubbery.
Evidence of environmental stress in the plants of that era reveals cycles of rain and drought, a pattern scientists call water stress. These conditions would have forced monkeys to rely on resources beyond fruit for portions of the year, underscoring the likelihood that leaf and foliage intake played a central role in survival during lean periods. Taken together, the findings portray Morotopithecus as inhabiting an open forest with abundant light gaps, where leafy meals could supplement sporadic fruit availability.
Early dental anatomy provides another clue about feeding habits. The molars of these primates were rugged and uneven, with pronounced cusps and valleys well-suited to tearing fibrous leaves rather than mashing soft fruit. This dental design points to a leaf-based diet rather than a fruit-heavy one, signaling a shift in dietary strategy among these ancient creatures.
Further insights come from examining tooth enamel and isotopic signatures in the enamel of Morotopithecus and contemporaneous mammals in the same geological layer. The isotope ratios indicate a preference for C3 type plants, which are typically woody shrubs and trees. In contrast, C4 plants tend to thrive in drier environments. These isotopic markers help illuminate the broader ecosystem and reinforce the idea that leaf consumption was an important, perhaps seasonal, food source for these early primates. The cumulative data from dental morphology and isotopic analysis strengthens the case for a leaf-oriented diet alongside occasional fruit consumption as a practical response to the habitat’s dynamic resources. Attributing these patterns to Morotopithecus paints a picture of an adaptive strategy deeply tied to environmental fluctuations and plant community composition, rather than a sole reliance on fruit or a static feeding niche. Researchers emphasize that this perspective fits with the broader understanding of primate evolution in changing climates and landscapes. Attribution: University of Michigan and associated researchers have contributed to this evolving view by combining fossil evidence, plant remains, and isotopic data to build a coherent narrative about leaf-based feeding and habitat use during this period.