Kelsey Pugh, a new lecturer in the Department of Anthropology, was the lead author of a study, along with scientists at the American Museum of Natural History and the Miquel Crusafont Catalan Institute of Paleontology, that reconstructed the well-preserved but damaged skull of a great ape species that lived about 12 million years ago.

The species, Pierolapithecus catalaunicus, may be crucial to understanding great apes and human evolution. The researchers describe their findings in the journal Proceedings of the National Academy of Sciences.

Pierolapithecus catalaunicus, a species from northeastern Spain first described in 2004, was one of a diverse group of now-extinct ape species that lived in Europe around seven to 15 million years ago. The species is key to understanding the mosaic nature of hominid (great ape and human) evolution because it is known from a cranium and partial skeleton of the same individual—a rarity in the fossil record.

“Features of the skull and teeth are extremely important in resolving the evolutionary relationships of fossil species, and when we find this material in association with bones of the rest of the skeleton, it gives us the opportunity to not only accurately place the species on the hominid family tree, but also to learn more about the biology of the animal in terms of, for example, how it was moving around its environment,” said Pugh, who is also a research associate at the American Museum of Natural History’s Division of Anthropology.

Kelsey Pugh

Kelsey Pugh holds a fossil she reconstructed for the study.

Pugh led the effort with her colleagues to virtually segment the CT scan—separating bone from matrix/sediment and separating fragments of bone—and create a virtual reconstruction of the face from this segmentation, along with the morphometric and evolutionary modeling analyses used to examine the evolution of the facial features of hominoids (apes and humans).

Previous work on Pierolapithecus suggests that an upright body plan preceded adaptations that allowed hominids to hang from tree branches and move among them. However, debate persists about the species’ evolutionary place, partly due to damage to the cranium.

“One of the persistent issues in studies of ape and human evolution is that the fossil record is fragmentary, and many specimens are incompletely preserved and distorted,” said co-author Ashley Hammond, associate curator and chair of the museum’s Division of Anthropology. “This makes it difficult to reach a consensus on the evolutionary relationships of key fossil apes that are essential to understanding ape and human evolution.”

From left: Pierolapithecus cranium shortly after discovery, after initial preparation, and after virtual reconstruction. Image credits: David Alba (left), Salvador Moyà-Solà (middle), Kelsey Pugh (right).

From left: The Pierolapithecus cranium shortly after discovery: after initial preparation, and after virtual reconstruction. (Image credits: David Alba, Salvador Moyà-Solà, and Kelsey Pugh.)

In an effort to bring clarity to these questions, the researchers used the CT scans to virtually reconstruct the cranium of Pierolapithecus, compare it to other primate species, and model the evolution of key features of ape facial structure. They found that Pierolapithecus shares similarities in overall face shape and size with both fossilized and living great apes, but it also has distinct facial features not found in other Middle Miocene apes. The results are consistent with the idea that this species represents one of the earliest members of the great apes and human family.

“An interesting output of the evolutionary modeling in the study is that the cranium of Pierolapithecus is closer in shape and size to the ancestor from which living great apes and humans evolved. On the other hand, gibbons and siamangs (the “lesser apes”) seem to be secondarily derived in relation to size reduction,” said co-author Sergio Almécija, a senior research scientist in the museum’s Division of Anthropology.

You can read more about the study in the The Washington Post.