Saturday, October 1, 2022

7.5-Million-Year-Old Gibbon Fossil Fills Gap in Evolutionary History of Apes

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Paleontologists have examined the fossilized remains of Yuanmoupithecus xiaoyuan, a small Old World monkey species that lived in China during the Late Miocene epoch.

Gibbons at play (c. 1427) by the Xuande Emperor, the fifth emperor of the Ming dynasty of China.

Yuanmoupithecus xiaoyuan lived what is now Yunnan in southern China between 8.2 and 7.1 million years ago.

First described in 2006, it belonged to Hylobatidae, the family of apes comprising the living gibbons and siamang.

The fossil record of the hylobatids is poorly known, being largely limited to fossil and subfossil remains from the Pleistocene and Holocene of China and Southeast Asia.

“The fossil remains of hylobatids are very rare, and most specimens are isolated teeth and fragmentary jaw bones found in cave sites in southern China and southeast Asia dating back no more than 2 million years ago,” sadi New York University’s Professor Terry Harrison.

“This new find extends the fossil record of hylobatids back to 7 to 8 million years ago and, more specifically, enhances our understanding of the evolution of this family of apes.”

In their research, Professor Harrison and colleagues examined the teeth and cranial specimens of Yuanmoupithecus xiaoyuan, including an upper jaw of an infant.

Using the size of the molar teeth as a guide, they estimated that the primate was similar in size to today’s gibbons, with a body weight of about 6 kg.

“The teeth and the lower face of Yuanmoupithecus xiaoyuan are very similar to those of modern-day gibbons, but in a few features the fossil species was more primitive and points to it being the ancestor of all the living species,” Professor Harrison said.

The paleontologists also found that Kapi ramnagarensis, which has been claimed to be an earlier species of hylobatid, based on a single isolated fossil molar from India, was not a hylobatid after all, but a member of a more primitive group of primates that were not closely related to modern-day apes.

“Genetic studies indicate that the hylobatids diverged from the lineage leading 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,” Professor Harrison said.

“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.”

A paper on the findings appears in the Journal of Human Evolution.

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Xueping Ji et al. 2022. The earliest hylobatid from the Late Miocene of China. Journal of Human Evolution 171: 103251; doi: 10.1016/j.jhevol.2022.103251

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