New discovery fills long-missing gap in evolutionary history

New discovery fills long-missing gap in evolutionary history

Upper jaw of the child of Yuanmoupithecus

The upper jaw of the child of Yuanmoupithecus. Credit: Terry Harrison, NYU . Anthropology Department

The oldest gibbon fossil was discovered in southwestern China.

The earliest gibbon fossil has been found by a team of researchers, filling a long-missing evolutionary gap in monkey history.

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

“Fossil remains of hylobatids are very rare, and most specimens are isolated teeth and fragmentary jawbones found in caves in southern China and Southeast Asia dating as little as 2 million years ago,” explains Terry Harrison, a professor in anthropology at the New York University and one of the authors of the article. “This new find extends the fossil record of hylobatids to 7 to 8 million years ago and, more specifically, improves our understanding of the evolution of this family of monkeys.”

The fossil, found in the Yuanmou area of ​​southwestern China’s Yunnan Province, belongs to a small monkey called Yuanmoupithecus xiaoyuan. The analysis of the study focused on the teeth and skull specimens of Yuanmoupithecusincluding an upper jaw from a young child who was less than two years old at the time of death.

Excavation at Leilao Village in Yunnan

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

Use the size of the molars as a guideline, Yuanmoupithecus was estimated to be nearly the same size as modern-day gibbons, weighing about 6 kilograms — or about 13 pounds.

“The teeth and lower surface of Yuanmoupithecus are very similar to today’s gibbons, but in some respects the fossil species was more primitive and indicates that it was the ancestor of all living species,” said Harrison, part of NYU’s Center for the Study of Human Origins.

Ji discovered the child’s upper jaw during a field survey, and by comparing it to modern gibbon skulls preserved 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 past 30 years that were housed at the Yunnan Institute of Cultural Relics and Archeology and the Yuanmou Man Museum.

“The remains of Yuanmoupithecus are extremely rare, but we have been diligent in recovering enough specimens to establish that the fossil monkey Yuanmou is indeed a close relative of the living hylobatids,” notes Harrison.

The Journal of Human Evolution study also found that Kapi ramnagarensisclaimed to be an earlier genus of hylobatid, based on a single isolated fossil molar from India, is nevertheless not a hylobatid, but a member of a more primitive group of primates not closely related to modern apes.

“Genetic studies indicate that the 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,” Harrison warns. . “With the 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 Earliest 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: 10.116/j.jhevol.2022.103251

The study was funded by the National Natural Science Foundation of China, the Yunnan Natural Sciences Foundation and the Strategic Priority Research 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 National Museum of Natural History at the Smithsonian Institution in Washington DC, among others while conducting their research.

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