Prehistoric ape gets a face

Skull of Pierolapithecus catalaunicus

Skull of “Pierolapithecus catalaunicus” shortly after discovery (left), after the first preparation (middle) and after the virtual reconstruction (right). © David M. Alba, Salvador Moyà-Solà and Kelsey Pugh

It is well known that we humans descend from the same ancestor as great apes. However, to date there are major gaps in our knowledge of the early evolution of our common family of hominids. The key to understanding this is the extinct great ape species “Pierolapithecus catalaunicus”, which lived a good twelve million years ago and was close to the common roots of hominids. Researchers have now reconstructed the face of this evolutionarily important species using a skull fossil. This provides new insights into facial development in great apes and humans.

During the geological period of the Middle Miocene - around 15 to 7 million years ago - a large number of hominoids lived in Europe. This group of anthropoids includes great apes (hominids) and humans, including the extinct great ape species “Pierolapithecus catalaunicus”. The evolutionary relationships between such extinct hominoids as well as living great apes and humans are often not known. 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 changed during fossilization.

Reconstructed skull and face of a prehistoric ape

A team led by Kelsey Pugh from the City University of New York has now examined one of these rare skull fossils using computer tomography. The fossil, which is around 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 broken into several pieces and therefore slightly distorted. Using the CT scans, Pugh and her colleagues digitally reassembled the fragments of the skull for the first time and thus reconstructed the hominid's three-dimensional face. The researchers compared this with 80 living and extinct species of human-like primates.

The result: The facial shape and size of P. catalaunicus most closely resembled 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 the extinct hominid, similar to these great apes, already had a relatively large and broad 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.

At the root of hominids, but not their ancestor

According to the researchers, this suggests that the prehistoric great ape P. catalaunicus developed very early from the common ancestor of great apes, but was not itself the last common ancestor. Instead, Pierolapithecus was probably an early branch in the family tree, evolving independently from the other proto-hominids from the common ancestor. Nevertheless, the facial reconstruction of this prehistoric ape 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 hominids differed in its general skull shape from all extant genera of great apes and from Pierolapithecus," report Pugh and her colleagues. The shape of the eye sockets was also different in the ancestor of all hominids. At the same time, the reconstructions confirm that this common ancestor was probably more similar to today's great apes and humans, with its rather large face, than to small great apes such as gibbons, as the team explains.

According to the authors, the results provide new insights into facial development in great apes. However, their conclusions represent only a preliminary hypothesis that can be reevaluated 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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