It is known that we humans are descended from the same ancestor as great apes. However, to date there are major gaps in our knowledge of the early evolution of our common hominin family. The key to understanding this is the extinct great ape species Pierolapithecus catalaunicus, which lived twelve million years ago and was close to the common roots of hominins. Researchers have now reconstructed the face of this evolutionarily important species using a fossil skull. This provides new insights into facial evolution in great apes and humans.
During the geological period of the Middle Miocene – about 15 to 7 million years ago – a large number of hominins lived in Europe. This group of hominins includes great apes (hominids) and humans, including the extinct great ape species Pierolapithecus catalaunicus. The evolutionary relationships between extinct hominins as well as great apes and humans are often unknown. This is due, among other things, to the fact that so far only a few fossil skulls of these species have been discovered and they are usually poorly preserved, incomplete or altered during fossilization.
Reconstruction of the skull and face of a prehistoric ape
A team led by Kelsey Pugh of the City University of New York examined one of these rare skull fossils using computer tomography. The fossil, which is about twelve million years old, is the only skull of a specimen of Pierolapithecus catalaunicus discovered so far. The fossil comes from northeastern Spain and is largely preserved, but is divided into several pieces and thus slightly deformed. Using CT scans, Pugh and her colleagues digitally reassembled parts of the skull for the first time, thus reconstructing the 3D human face. The researchers compared this with 80 living and extinct species of human-like primates.
The result: the shape and size of P. catalaunicus’s face closely resembles living and extinct great ape species in the region of the great ape family tree where gorillas and orangutans are also found. The face of extinct human ancestors, similar to these great apes, had a relatively large and wide middle face with high-set eyes and a flat, broad nose. However, there were also clear differences, for example in the shape of the jaw.
In the root of humans, but not their ancestors
According to the researchers, this suggests that the prehistoric great ape P. catalaunicus evolved very early from the common ancestor of great apes, but was not itself the last common ancestor. Alternatively, Perolapithecus may have been an early branch in the family tree, evolving independently from other protozoans of the common ancestor. However, a reconstruction of this prehistoric ape’s face provides valuable information about what this common ancestor once looked like.
“The combined results of our 2D and 3D analyzes indicate that the last common ancestor of all hominins differed in its general skull shape from all extant genera of great apes and from Peyrolapithecus,” Pugh and her colleagues said. The shape of the eye sockets was also different in the ancestors of all humans. Meanwhile, the reconstructions confirm that this common ancestor may have been more similar to today’s great apes and humans, with its rather large face, than to small great apes like gibbons, the team explains.
According to the authors, the results provide new insights into facial evolution in great apes. However, their conclusions represent only a preliminary hypothesis that can be re-evaluated as new fossils are discovered.
Source: Kelsey Pugh (City University of New York) et al., Proceedings of the National Academy of Sciences (PNAS), doi: 10.1073/pnas.2218778120
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