Orangutans are the sole survivors of a major radiation of great apes across Eurasia, from Spain to China, in the Miocene, which began about 23 million years ago. By the late Miocene, most of these species had become extinct, but fossil records show that the Yunnan region of southwestern China continued to harbor great apes well into the terminal Miocene. However, why these holdout hominoids eventually disappeared too has been unclear.
Now Li et al. have found that from 6.2 million to 5 million years ago, periodic cooling interrupted a generally warm, humid climate in the Yunnan region, potentially triggering changes in vegetation that provided food for great apes and contributing to their disappearance.
Evidence for these cool episodes came from a sediment core collected in an ancient Yunnan lake bed. The core contains materials deposited between 8.8 million and 2.6 million years ago. Analysis of the chemical composition of the sediments at different points in the core revealed evidence of chemical weathering processes that indicate what the climate was like when the different layers of sediment were deposited.
The analysis suggests that conditions were generally warm and humid from 8.8 million to 6.2 million years ago, despite a gradual cooling trend. However, between 6.2 million and 5 million years ago, three pulses of strong climatic cooling occurred amid the warmer background climate. After 5 million years ago, the region’s climate continued to cool.
The sediment core was extracted about 500 meters from where the youngest known Miocene great ape fossil—the cranium of an individual of the Lufengpithecus genus—was discovered. At about 6.1 million years old, the fossil’s age corresponds to the strongest of the three cooling episodes, which, according to the authors, is in line with the idea that these episodes and their effects on vegetation could have promoted the local disappearance of great apes.
The authors note that the precise timing of great apes’ disappearance in the Yunnan region is unknown and that further research is needed to confirm whether they indeed went extinct or they evolved into a different lineage in other regions. (Geophysical Research Letters, https://doi.org/10.1029/2020GL087741, 2020)
—Sarah Stanley, Science Writer