The 2,500 giant pandas that are alive in the wild today dwell in the Shaanxi, Gansu, and Sichuan provinces of central China. But scientists believe the bears once had a much greater range, roaming through southern China, Vietnam and Myanmar.
Little is known about how these extinct pandas were related to the fluffy creatures that we know and love, so scientists were excited when they found a fossilized panda skull in a cave in southern China in 2014. As Erika K. Carlson reports for Discover, researchers at the Chinese Academy of Sciences recently sequenced the bear’s mitochondrial genome—and discovered that the ancient animal represents an entirely new panda lineage.
The skull, which is around 22,000 years old, was unearthed in Cizhutuo Cave in China’s Guangxi Province, a region now devoid of pandas. Though the fossil was discovered in a hot and humid environment, which is not conducive to the preservation of DNA, researchers were able to piece together 148,326 fragments of the bear’s mitochondrial DNA to create a complete genomic sequence, according to a report published recently in Current Biology. The newly sequenced genome represents the oldest known panda DNA.
Researchers compared the reconstructed genome to mitochondrial genomes from 138 extant bears and 32 ancient bears to create a family tree, explains a press release announcing the new research. The team found that the Cizhutuo panda split from living giant pandas around 183,000 years ago. The ancient bear also had 18 genetic mutations that may be linked to the panda’s distinct southern habitat or to climate differences during the Last Glacial Maximum.
These findings suggest that “the Cizhutuo panda, while genetically more closely related to present-day pandas than other bears, has a deep, separate history from the common ancestor of present-day pandas," Qiaomei Fu, a paleogenomics expert at the Chinese Academy of Sciences, explains in the statement.
Moving forward, the researchers hope to sequence a genome from the ancient panda’s nuclear DNA, which is found in the nucleus of a cell. As Jessica Boddy writes in Gizmodo, it was easier for the researchers to extract mitochondrial DNA, which exists in the cell’s mitochondria, from the panda skull because there are about 1,000 copies of mitochondrial DNA in any given cell. By contrast, there are only two copies of nuclear DNA.
Because mitochondrial DNA is passed from mothers to their children, however, it cannot give a complete picture of an individual’s lineage. Nuclear DNA contains information from both parents and so, as Fu explains in the statement, studying the Cizhutuo panda’s nuclear DNA “would allow a more thorough analysis of the evolutionary history of the Cizhutuo specimen, as well as its shared history with present-day pandas."