https://www.sciencedirect.com/science/article/abs/pii/S0047248422001117
October 2022

Abstract
Yuanmoupithecus xiaoyuan, a small catarrhine from
the Late Miocene of Yunnan in southern China, was
initially suggested to be related to Miocene
proconsuloids or dendropithecoids from East Africa,
but subsequent reports indicated that it might be
more closely related to hylobatids. Here, detailed
comparisons of the material, including seven newly
discovered teeth and a partial lower face of a
juvenile individual, provide crucial evidence to
help establish its phylogenetic relationships.
Yuanmoupithecus exhibits a suite of synapomorphies
that support a close phylogenetic relationship
with extant hylobatids. Furthermore, based on the
retention of several primitive features of the
dentition, Yuanmoupithecus can be shown to be the
sister taxon of crown hylobatids. The contention
that Kapi ramnagarensis from the Middle Miocene of
India might represent an earlier species of
hylobatid is not supported here. Instead, Kapi is
inferred to be a specialized pliopithecoid more
closely related to Krishnapithecus krishnaii from
the Late Miocene of India. Currently then,
Yuanmoupithecus represents the earliest known
definitively identified hylobatid and the only
member of the clade predating the Pleistocene. It
extends the fossil record of hylobatids back to
7–8 Ma and fills a critical gap in the evolutionary
history of hominoids that has up until now remained
elusive. Even so, molecular estimates of a
divergence date of hylobatids from other hominoids
at about 17–22 Ma signifies that there is still a
substantial gap in the fossil record of more than
10 million years that needs to be filled in order
to document the biogeographic origins and early
evolution of hylobatids.