The closest living relatives of humans are the great apes, such as chimpanzees, gorillas, orangutans, and gibbons. We all had a common ancestor who lived in the Miocene epoch (23 million to 5 million years ago). While scientists have no remains of this mysterious creature, what could it have looked like?

In other words, how big was our last common ancestor (CAO) according to the available evidence, and what did its skull, brain, legs, arms, and even fingers look like?

We don’t have all the answers. But the closest relatives alive today may be gorillas and chimpanzees.

“The size of the OSP is a big unknown,” said Christopher Gilbert, a paleoanthropologist at Hunter College at the City University of New York. This is due to the scarcity of great ape fossils from the OSP period, according to a 2017 study in the journal Nature.

“The first apes had a wide range of body sizes, from small gibbon species to larger primates approaching the gorilla, and this makes it difficult to determine the weight of OSP without better understanding the evolutionary relationships and history of these species,” Gilbert said. Co-author of the Nature study. .

Modern evidence indicates that OSP was probably a four-legged animal. The fossils show that trunked apes had vertical climbing and hanging behaviors, just as modern humans could use their arms to hang from tree branches. However, unlike all living apes that prefer to hang between or under the branches of trees, at least some great apes do not specialize in hanging behavior, lacking adaptations such as long, strongly curved fingers and toes and very mobile wrists and shoulders. and hips. Gilbert said that means that OSP isn’t expert in suspension either.

“It’s possible that OSP walked on two legs, like a human, and could have walked on two legs,” said Thomas Cody Prang, a paleoanthropologist at the University of Washington in St. “However, because OSP is quadrupedal like other primates, it probably didn’t walk on two legs, but instead used all four.”

“The great apes showed different head shapes. Some had gibbon-like skulls with short faces, while others had longer faces that resembled primitive apes and Old World monkeys such as baboons (Papio genus) and macaques (Macaca genus),” Prang said. We know with almost certainty that the size of the OSP brain is smaller than the size of the human brain.”

“The hands and feet of early great apes are poorly preserved in the fossil record. However, the upper limbs of early hominins (humans and our close relatives and ancestors) appear large and robust in relation to forelimb-dominated movement, namely climbing and hanging,” he said. “In terms of legs, early hominins appear to have short hind limbs, making them more like great apes – gorillas (Gorilla gorilla and Gorilla beringei), chimpanzees (Pan troglodytes), orangutans (Pongo genus), and bonobos (Pan paniscus)—than humans, He said. Essentially, early hominins seem to have been designed for treetops rather than open savanna.

As for the hands, 2021 research in the journal Science Advances and colleagues studied Ardipithecus, a 4.4-million-year-old early hominin fossil, and found that its hand most closely resembled that of chimpanzees and bonobos. This may indicate that the last common ancestor had long, curved fingers.

“Humans, chimpanzees, gorillas and bonobos walk with their heels on the ground, which suggests that OSP is doing the same,” Prang said.

This form of locomotion is also often associated with other traits seen in living African great apes (gorillas, chimpanzees, and bonobos), such as the use of knuckles to assist walking and evolutionary adaptations for vertical climbing. “All the features we can reasonably examine suggest that the earliest hominins, and thus possibly OSP, were characterized by the same components of this adaptive package,” Prang said. “OSP was neither a gorilla nor a chimpanzee, but it probably looked most like a gorilla and a chimpanzee.”

Overall, OSP’s appearance is “still a highly controversial issue,” Gilbert said. New fossils will need to be discovered to complete the picture.