New discovery fills long-missing gap in evolutionary history

The oldest gibbon fossil has been discovered in southwestern China.

The oldest gibbon fossil has been discovered by a team of researchers, filling a long-missing evolutionary gap in ape history.

The study, which was published in the Journal of Human Evolutionfocuses on the family of Hylobatidae monkeys, which includes 20 species of living gibbons found throughout tropical Asia, from northeast India to Indonesia.

“Fossil remains of Hylobatidae are very rare, and most specimens are isolated teeth and fragmentary jaw bones found in caves in southern China and Southeast Asia dating from no later than no more than 2 million years ago,” says Terry Harrison, professor of anthropology in New York. University and one of the authors of the article. “This new discovery extends the fossil record of Hylobatidae to 7-8 million years ago and, more specifically, improves our understanding of the evolution of this family of apes.”

The fossil, found in the Yuanmou region of Yunnan province in southwest China, is of a small monkey called Yuanmoupithecus xiaoyuan. The study’s analysis focused on teeth and cranial specimens of Yuanmoupithecuswhich included an upper jawbone from a young child who was under two years old at the time of his death.

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

Using molar size as a guide, Yuanmoupithecus was estimated to be close in size to modern gibbons, with a body weight of around 6 kilograms, or about 13 pounds.

“The teeth and lower face Yuanmoupithecus are very similar to those of modern gibbons, but in a few features the fossil species was more primitive and indicates that it is the ancestor of all living species,” observes Harrison, who is part of the Center for the Study of Human Origins of NYU.

Ji discovered the child’s upper jaw during field investigation, and by comparing it with modern gibbon skulls held 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 specimens collected over the previous 30 years that were housed at the Yunnan Institute of Cultural Relics and Archeology and the Yuanmou Museum of Man.

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

The Journal of Human Evolution study also revealed that Kapi ramnagarensiswhich has been claimed to be an earlier species of hylobatid, based on a single 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 the modern monkeys.

“Genetic studies indicate that hylobatids diverged from the lineage leading to great apes and humans around 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, it is hoped that additional discoveries will help fill these critical gaps in the evolutionary history of hylobatids.”

Reference: “The first Late Miocene hylobatid of China” by Xueping Jia, Terry Harrison, Yingqi Zhang, Yun Wub, Chunxia Zhang, Jinming Hui, Dongdong Wua, Yemao Hou, Song Li, Guofu Wang and Zhenzhen Wang, September 13, 2022 , 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 Research Program of the Chinese Academy of Sciences.

The researchers also had access to the skeletal and paleontological collections of the American Museum of Natural History in New York and the National Museum of Natural History at the Smithsonian Institution in Washington DC, among others, as part of their study.