A team of University of Kansas researchers has discovered a "mother lode" of primate fossils in southern China that reveal the effects of ancient climate change on six new species. The fossils originate from just after the Eocene-Oligocene transition approximately 34 million years ago when a drastic global cooling rendered Asia inhospitable to primates, significantly reducing their populations.
"At the Eocene-Oligocene boundary, because of the rearrangement of Earth's major tectonic plates, you had a rapid drop in temperature and humidity," said K. Christopher Beard of the University of Kansas and co-author of the study. "Primates like it warm and wet, so they faced hard times around the world - to the extent that they went extinct in North America and Europe."
"Of course, primates somehow survived in Africa and Southern Asia, because we're still around to talk about it," he added.
Although previous evidence points to the earliest anthropoids - monkeys, apes and humans - originating in Asia, the fact that they eventually ended up in Africa has always baffled scientists. Now, the current study reveals the reason: severe climate change wiped out Asian anthropoids, leaving the only place left for evolution as Africa.
The study is the result of a decade's worth of fieldwork at a site in southern China, a region that was likely sought out by primates due to its warmer temperatures. The jaw and tooth fragments that were used to describe the six new species likely survived due to their tough enamel surfaces.
"The fossil record usually gives you a snapshot here or there of what ancient life was like," Beard said. "You typically don't get a movie."
"We have so many primates from the Oligocene at this particular site because it was located far enough to the south that it remained warm enough during that cold, dry time that primates could still survive there," he continued. "They crowded into the limited space that remained available to them."
If the intense global cooling that took place during the Eocene-Oligocene transition had not taken place, primates would likely have continued to evolve in Asia instead of making their way to Africa, eventually leading to the evolution of humans.
The results of the University of Kansas study highlight the vulnerability of primates to climate change even millions of years ago.
"This is the flip side of what people are worried about now," Beard said. "The Eocene-Oligocene transition was the opposite of global warming - the whole world was already warm, then it cooled off. It's kind of a mirror image. The point is that primates then, just like primates today, are more sensitive to a changing climate than other mammals."
The findings were published in the May 6 issue of the journal Science.
