https://www.pnas.org/doi/10.1073/pnas.2218778120
The reconstructed cranium of Pierolapithecus and
the evolution of the great ape face

Significance
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/or distorted. 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. Here, we
reconstruct the face of Pierolapithecus catalaunicus
and analyze its morphology in an evolutionary
framework. Our results are consistent with the
hypothesis that this species represents a basal
member of the group including great apes and humans,
and provide insight into the facial morphology of
the ancestor of the group.

Abstract
Pierolapithecus catalaunicus (~12 million years ago,
northeastern Spain) is key to understanding the
mosaic nature of hominid (great ape and human)
evolution. Notably, its skeleton indicates that an
orthograde (upright) body plan preceded suspensory
adaptations in hominid evolution. However, there is
ongoing debate about this species, partly because
the sole known cranium, preserving a nearly
complete face, suffers from taphonomic damage. We
1) carried out a micro computerized tomography (CT)
based virtual reconstruction of the Pierolapithecus
cranium, 2) assessed its morphological affinities
using a series of two-dimensional (2D) and
three-dimensional (3D) morphometric analyses, and
3) modeled the evolution of key aspects of ape face
form. The reconstruction clarifies many aspects of
the facial morphology of Pierolapithecus. Our
results indicate that it is most similar to great
apes (fossil and extant) in overall face shape and
size and is morphologically distinct from other
Middle Miocene apes. Crown great apes can be
distinguished from other taxa in several facial
metrics (e.g., low midfacial prognathism,
relatively tall faces) and only some of these
features are found in Pierolapithecus, which is
most consistent with a stem (basal) hominid
position. The inferred morphology at all ancestral
nodes within the hominoid (ape and human) tree is
closer to great apes than to hylobatids (gibbons
and siamangs), which are convergent with other
smaller anthropoids. Our analyses support a
hominid ancestor that was distinct from all extant
and fossil hominids in overall facial shape and
shared many features with Pierolapithecus. This
reconstructed ancestral morphotype represents a
testable hypothesis that can be reevaluated as
new fossils are discovered.

The reconstruction in the figures is amazing.

"While it is broadly accepted that
Pierolapithecus represents a hominid, and our
results support this hypothesis, the question of
its relationship to extant hominid subfamilies
is more contentious."

"...the inferred position of the hominid node
in the 3D phylomorphospace (Fig. 3) suggests
that, in overall facial shape, the hominid LCA
is perhaps closer to Gorilla or Pongo than to
Pan or Pierolapithecus."