In 1935, anthropologist Gustav von Koenigswald came across several strange teeth in drug stores in Hong Kong and southern China. The specimens, sold as “dragon teeth,” to be ground up for use in Chinese medicine, were special: They were apelike, but huge—much bigger than the molars of any other fossil or living primates. Their size (and that of four fossilized jaw bones) suggested that Gigantopithecus blacki was the largest primate ever discovered, towering nearly 3 meters in height. But without any skulls or skeletons, researchers didn’t know whether the animal, which lived from roughly 2 million to 200,000 years ago, was a relative of today’s orangutans, today’s African apes, or something else entirely.
Now, by piecing together clues from proteins in the enamel of a 1.9-million-year-old tooth found in Chuifeng Cave in southern China, researchers have evidence that at last allows them to place G. blacki on the primate family tree. The work solves a long-standing evolutionary puzzle and demonstrates that genetic information can survive in proteins much longer—and under more difficult conditions—than many people had thought.
Frido Welker, an evolutionary geneticist at the University of Copenhagen, and his colleagues set out to examine G. blacki teeth for intact pieces of proteins called peptides, which may be preserved for up to a few million years—far longer than more fragile DNA. Welker and his colleagues dissolved tiny amounts of enamel from a G. blacki molar and used mass spectrometry to identify more than 500 peptides that matched six proteins. By comparing the amino acids to those in the same six proteins in living apes, including orangutans, gorillas, and other apes and monkeys, they calculated that the giant ape was most closely related to orangutans. The two lineages probably split off between 10 million and 12 million years ago, they report today in Nature.
That’s not completely unexpected, says paleoanthropologist Russell Ciochon of the University of Iowa in Iowa City, who wasn’t involved in the study. But having direct molecular evidence—especially of the timing of the split—is exciting. The work also shows for the first time that fossil teeth can retain usable genetic information for millions of years in hot and humid regions where organic matter breaks down faster. Although the tooth itself is just shy of 2 million years old, the warm temperatures of the cave (an average of 20°C) pushes its so-called “thermal age” to 12 million years—about five times the thermal age of any other skeletal proteins sequenced to date. “Now, we know that we can retrieve [genetic information] from something that is almost 2 million years old from a subtropical environment,” says University of Copenhagen paleogeneticist Enrico Cappellini, who helped lead the project with Welker.
The key, he says, was to focus on the enamel proteins. Both before and after death, the minerals in tooth enamel keep water out and help the tooth resist decomposition. The success with G. blacki suggests enamel from other fossil teeth might help sort out the relationships between other early apes, Ciochon says, including how G. blacki was related to great apes that lived in India and Pakistan. And because 12 million years is close to the thermal age of many intriguing fossils in the human lineage, Cappellini says, “This brings us closer to thinking it could be feasible to investigate hominins from Africa. It’s at least possible.”