(CN) — Professor Nikolai Spassov’s interest in two mysterious fossilized teeth — an upper carnassial tooth and an upper canine — in the bowels of the Bulgarian National Museum of Natural History goes back to the beginning of his career. Deepening the mystery was that no one knew what species the teeth belonged to.
Back in the 1970s, paleontologist Dr. Ivan Nikolov catalogued the teeth as part of a collection of fossils unearthed in northwestern Bulgaria. When Spassov’s paleontological career began in the 1980s, his main clue was a single, nearly indecipherable handwritten label.
“It took me many years of returning from time to time to this find to decipher the name of the locality and what its age was,” Spassov said in an email. More started to make sense after a new genus of fossil panda was found in China and two new genera in Europe. “This helped me realize that I was holding in my hands unique fossils representing a new species of giant panda.”
Spassov conferred with Qigao Jiangzuo of China’s Peking University, who co-wrote the study as an expert in study the giant panda’s evolution. After the two found enough similarities between the modern giant panda and the teeth, they definitively concluded the fossils belonged to an ancient giant panda species.
To honor the paleontologist who found the fossils, Spassov named the new species Agriarctos nikolovi, according to the study published in the peer-reviewed Journal of Vertebrate Paleontology.
However, where there were similarities, there were also interesting differences. Unlike China’s extinct panda Ailurarctos, whose evolution focused heavily on eating bamboo, A. nikolovi had a more varied diet.
According to Spassov, he and Jiangzuo “hypothesize that the new species, as well as its Chinese fossil relative, the putative ancestor of the giant panda, which lived at the same time, 7-6 million years ago [Ailurarctos lufengensis], were not specialized to feed on bamboo: the surface of their teeth do not have those massive and thick cusps capable of withstanding the grinding of such hard food as bamboo. They obviously ate vegetable, but not so hard.”
At least, the study argues, A. nikolovi’s teeth were strong enough to fight off predators. The canines are comparable in size to the modern panda’s, suggesting that they were the same size as modern pandas or slightly smaller.
However, the study suggests that these existing predators further pushed the pandas toward vegetarianism.
“The likely competition with other species, especially carnivores and presumably other bears, explains the closer food specialization of giant pandas to vegetable food in humid forest conditions,” stated Spassov.
Ultimately, Spassov proposes that what caused the species’ extinction was a current enemy of many species – climate change. Specifically, the “Messinian salinity crisis.”
Coal deposits imbued with a blackened hue on the teeth suggest that A. nikolovi inhabited forested, swampy regions. Spassov said when the Mediterranean basin dried up, it is likely that climate change turned the swamps arid.
“Giant pandas are a very specialized group of bears,” added Spassov. “Even if A. nikolovi was not as specialized in habitats and food as the modern giant panda, fossil pandas were specialized enough and their evolution was related to humid, wooded habitats.”
Even as Spassov and Jiangzuo hypothesized about the end of A. nikolovi, something else came up in their research. Jiangzuo realized that the species belonged to the Ailuropodini, a tribe of the Ursidae bear family.
They came up with two theories. The first was that the modern giant panda is a direct descendant of A. nikolovi given their similarities in bound structure and size. However, wrote Spassov, he leans toward the second theory that A. nikolovi and Ailuropoda melanoleuca are parallel evolutions of each other.
“The Chinese Ailurarctos is the probable direct ancestor, because of some details in the proportions and shapes of the tooth cusps (particularly the upper carnassial tooth), which show a more close resemblance to today's panda," he said. "Future finds would show how right we are and how much the new species from the Balkans has in common with the origin of the giant panda.”
So as the last European panda faded from existence, part of them may still live on in their close relatives — the modern giant panda.
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