Most modern apes are pretty big. The four great apes—gorillas, orangutans, chimpanzees and bonobos—can weigh in at over 100 pounds. Even the lesser apes, the gibbons, can weigh as much as 30 pounds. Comparatively, as Nicholas St. Fleur at The New York Times reports, a newly discovered fossil species of ape is teeny tiny. Weighing in at less than 8 pounds, Simiolus minutus is believed to be the smallest ape species ever found.
In 2004, researchers discovered a little fossilized molar in the Tugen Hills of Kenya in a layer dating back about 12.5 million years ago during the Miocene epoch. When they compared it to other fossils, they discovered they were similar to two teeth previously recovered in the area. An examination of the fossils showed that they belonged to a tiny ape species. When the paleontologists extrapolated the size of the animal based on the teeth, they found it was likely under 8 pounds, smaller than an average house cat. The research appears in the Journal of Human Evolution.
More surprising, the morphology of its molars showed that it was adapted to eating fruit and leaves in trees. But that may have spelled its doom. As the little ape species headed into the canopy, the rise of the colobine monkeys was just beginning as evidenced by other fossil teeth found in the same area. The agile monkeys were likely able to outcompete the apes when it came to accessing the most nutritious leaves. Unlike apes, monkeys have tails that help them balance while running along the tops of branches. Structurally, they are more like other four-legged mammals than apes, who use their strong arms to pull themselves between branches. The little ape just may not have been able to keep up with the bands of leaf-munching monkeys or folivores.
“One thing this shows us is that some apes were leaning toward folivory at just the time when monkeys were evolving their uniquely effective adaptations for it,” co-author James Rossie of Stony Brook University says in a press release. “Under those circumstances, I’m not surprised that this is the last you see of these small apes. We’ve previously found the earliest colobine monkeys at these sites, and now we have an ape that looks like it would have been in direct competition with them for food.”
The monkeys, it turns out, were also more able to digest the leaves and extract energy from them, whereas the apes did not have the same plumbing. “They were trying to do what colobines were doing, which was foolish because no one had that same equipment,” Rossie tells St. Fleur of the Times. “They brought a knife to a gunfight and then found out the knife was a plastic picnic knife.”
The finding might shed some light on what happened during the middle to late Miocene, which took place roughly 14 million to 5 million years ago. It was around 8 million years ago when climate change began to turn the forests that apes in Africa and southern Europe roamed into grasslands, pushing many species to extinction. From a wide variety of ape species—ranging from the newly discovered tiny ape to creatures weighing around 110 pounds—and just a handful of monkey species, recent research suggests that during this time of change, monkeys were able to take over the niches left by the apes, meaning by the end of the Miocene there were lots of monkeys around but just a few apes.
As St. Fleur of the Times points out, that trend toward more monkeys and fewer apes remains true today, with 130 species of Old World Monkeys inhabiting Asia and Africa and just 20 species of apes remaining. The current hypothesis is that environmental changes and heavy competition from the monkey species caused the Planet of the Apes to slowly morph into the Planet of the Monkeys.
While competition for food may have spelled the demise of the smallest ape, recent research indicates the world’s largest ape species also had trouble putting dinner on the table. Gigantopithecus, which stood 10 feet tall and weighed up to 1,100 pounds, survived for several million years in forests in modern-day southern China. But around 100,000 years ago, when the world cooled and many forests transformed into savannahs, the mega-ape simply was not able to fill its daily caloric need and joined Simiolus in the annals of ape history.