Researchers have dug up the remains of a 22,000-year-old fossil that belongs to a long-lost bear believed to be the cousin of the giant panda.
The ancient remains were unearthed in Guangxi province in southern China. Following a sequencing of the fossil's mitochondrial genome, the researchers have concluded that the ancient animal was not a direct ancestor of the modern-day panda but a relative that belonged to a parallel lineage that split away thousands of years ago.
Unearthing An Ancient Panda
In a new paper published in the journal Current Biology, a team of anthropologists at Beijing's Chinese Academy of Sciences describes the challenges they encountered in extracting the mitochondrial DNA required to establish the fossil's origin.
The 22,000-year-old jaw was actually discovered back in 2014 by paleoanthropologist Yingqi Zhang. Back then, Zhang was absorbed in looking for the remains of the Gigantopithecus, believed to be the biggest primate that ever lived.
Descending into a sinkhole in Cizhutuo Cave, Zhang failed to find traces of the Gigantopithecus. He did, however, found an ancient jaw that looked, to the naked eye, exactly like that of a giant panda.
Because Zhang was so focused on the quest to find the largest primate, the panda jaw remained untouched, wrapped in tissue paper in a box on one of the shelves in his office, until one of his colleagues, who had been trying and failing to extract panda DNA from ancient remains, caught wind of Zhang's discovery.
Mapping The Ancient Panda's DNA
For anthropologist Qiaomei Fu, the challenge of sequencing the genome of the ancient panda almost proved futile. For one thing, the fossil was located in the subtropical province of Guangxi, where the delicate strands of DNA can easily break down due to the high heat and humidity.
Fu's first attempt at extracting DNA from the fossil was, in fact, unsuccessful. However, after performing a CT scan to look for the cochlea, a spiral-shaped cavity in the inner ear known to be excellent at preserving DNA in humans, Fu and her team were able to extract nearly 150,000 fragments of mitochondrial DNA from the fossil.
The researchers then aligned the ancient panda's fragmented mitochondrial DNA with that of modern-day pandas to retrieve the missing pieces from the ancient animal's genome. This led to the discovery of an ancient lineage of the beloved bear that split away from the main branch of pandas 183,000 years ago.
They also found 18 genetic mutations that changed the structure of proteins in six of the ancient panda's mitochondrial genes. The researchers believe the mutations may have been the animal's natural response to the subtropical climate of its habitat.
The use of mitochondrial DNA, however, provides an incomplete picture. Mitochondrial DNA is DNA found in the mitochondria of cells. Compared to nuclear DNA, which only has two copies in the nucleus, (mt)DNA is far easier to extract because it has 1,000 copies.
However, (mt)DNA only contains genetic information passed on from the maternal side. Fu says they are planning to look into the fossil's nuclear DNA to help them find more information about the ancient animal, including if it had the same black-and-white coat of the modern-day beloved bear.
"This really highlights that we need to sequence more DNA from ancient pandas to really capture how their genetic diversity has changed through time and how that relates to their current, much more restricted and fragmented habitat," Fu says.
Pandas More Diverse Than Previously Thought
The finding provides new evidence that giant pandas, one of the eight bear species in the world, are more diverse than previously thought.
Modern-day pandas are situated only in three provinces in China: Gansu, Sichuan, and Shaanxi. Only 2,500 of this vulnerable species remain in conservation areas, making it difficult for researchers to create a comprehensive view of the panda's genetic history.
However, the latest find was unearthed in Guangxi, where no giant pandas exist today. Earlier fossil discoveries have shown that pandas lived in various places in China, Myanmar, Vietnam, and even as far as Spain and Hungary.
One fossil dating back to 8,000 years ago suggests that it belonged to another relative of the modern panda, an animal that branched off some 62,000 years ago.
