The new discovery fills a long-missing gap in evolutionary history

The new discovery fills a long-missing gap in evolutionary history

Upper jaw of baby Yuanmoupithecus

The upper jaw of a newborn Yuanmoupithecus. Credit: Terry Harrison, NYU Department of Anthropology

The oldest gibbon fossil was discovered in southwest China.

A team of researchers has found the earliest gibbon fossil, filling a long-missing evolutionary gap in ape history.

The study, which was published in Journal of Human Evolutionfocuses on the hylobatid monkey family, which consists of 20 species of living gibbons found throughout tropical Asia from northeastern India to Indonesia.

“Fossil remains of hylobatids are very rare, with most specimens being isolated teeth and fragmented jawbones found in caves in southern China and Southeast Asia, dating back no more than 2 million years,” explains Terry Harrison, professor of anthropology at New York University and one of the authors of the paper. “This new discovery extends the fossil record of hylobatids from 7 to 8 million years ago and, more specifically, improves our understanding of the evolution of this ape family.”

The fossil, found in the Yuanmou area of ​​Yunnan province in southwest China, belongs to a small monkey called Yuanmoupithecus xiaoyuan. The study’s analysis concentrated on teeth and skull samples Yuanmoupithecuswhich includes the upper jaw of a young child who was less than two years old at the time of death.

Excavation near the village of Leilao in Yunnan

An excavation near the village of Leilao in Yunnan, one of the sites where Yuanmoupithecus remains were found. Credit: Terry Harrison, NYU Department of Anthropology

Using molar size as a guide, Yuanmoupithecus it was estimated to be about the same size as today’s gibbons, with a body weight of about 6 kilograms – or about 13 pounds.

“Teeth and lower face Yuanmoupithecus are very similar to those of today’s gibbons, but in several features the fossil species was more primitive and indicates that it is the ancestor of all living species,” notes Harrison, part of NYU’s Center for the Study of Human Origins.

Ji discovered the child’s upper jaw during field research, and by comparing it with modern gibbon skulls kept at the Kunming Institute of Zoology, he was able to identify it as a hylobatid. In 2018, he invited Harrison and other colleagues to work on samples collected over the previous 30 years housed at the Yunnan Institute of Cultural Relics and Archeology and the Yuanmou Man Museum.

“The remains of Yuanmoupithecus are extremely rare, but with diligence, it was possible to find enough specimens to determine that the fossil monkey Yuanmou is indeed a close relative of living hylobatids,” notes Harrison.

The Journal of Human Evolution the study also found that Kapi ramnagarensisclaimed to be an earlier species of hylobatid, based on an isolated fossil molar from India, is not a hylobatid after all, but a member of a more primitive group of primates not closely related to today’s monkeys.

“Genetic studies show that hylobatids diverged from the lineage that led to the great apes and humans about 17 to 22 million years ago, so there is still a 10-million-year gap in the fossil record that needs to be filled,” warns Harrison. “With continued exploration of promising fossil sites in China and elsewhere in Asia, we hope that additional discoveries will help fill these critical gaps in the evolutionary history of hylobatids.”

Reference: “The earliest hylobatid from the Late Miocene of China” by Xueping Ji, Terry Harrison, Yingqi Zhang, Yun Wub, Chunxia Zhang, Jinming Hui, Dongdong Wua, Yemao Hou, Song Li, Guofu Wang, and Zhenzhen Wang, 213 Sep 2020 . Journal of Human Evolution.
DOI: 10.1016/j.jhevol.2022.103251

The study was funded by the National Natural Science Foundation of China, the Yunnan Natural Science Foundation and the Strategic Priority Program of the Chinese Academy of Sciences.

The researchers also gained access to skeletal and paleontological collections at the American Museum of Natural History in New York and the Smithsonian Institution’s National Museum of Natural History in Washington, D.C., among others, while conducting their study.

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