A "mother lode" of newly found fossil primates in southern China strengthens evidence that primates first emerged in Asia, with climate change later shifting the evolution of monkeys, apes and even our own species to Africa.
The findings, published in the journal Science, help explain the Asia-Africa story of primate evolution and also demonstrate how sensitive humans and other primates are to climate change.
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"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," co-author K. Christopher Beard, senior curator at the University of Kansas' Biodiversity Institute, said in a press release.
"Of course," he added, "primates somehow survived in Africa and Southern Asia, because we're still around to talk about it."
Beard and his colleagues discovered six new species of fossil primates dating to 34 million years ago from southern China. All that's left of the primates now are jaw and tooth fragments, which survived so long due to their tough enamel surfaces.
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"The fossil record usually gives you a snapshot here or there of what ancient life was like. You typically don't get a movie," Beard said.
He continued: "We have so many primates from the Oligocene (approximately 34–23 million years ago) 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. They crowded into the limited space that remained available to them."
Some primates had previously migrated to North America, Europe and other parts of Asia. As Beard mentioned, those early populations eventually died out. This was due to a drastic cooling that took place around 34 million years ago. The dramatic change in climate made much of Asia inhospitable to primates, slashed their populations and rendered discoveries of such fossils especially rare, making the new fossil finds all the more important.
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Like most of today's primates, the ancient Chinese ones were tropical tree-dwellers, according to the researchers. One of the species, named Oligotarsius rarus, was "incredibly similar" to the modern tarsier found today only in the Philippine and Indonesian islands, they wrote.
"If you look back at the fossil record, we know that tarsiers once lived on mainland Asia, as far north as central China," Beard said. "The fossil teeth described in this paper are nearly identical to those of modern tarsiers. Research shows that modern tarsiers are pretty much living fossils - those things have been doing what they do ever since time immemorial, as far as we can tell."
If the global intense cooling had not occurred 34 million years ago, the main stage of primate evolution may have continued to be in Asia, rather than transitioning to Africa, where it is believed our species eventually emerged.
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While humans today have tools to combat cold weather, our species, and certainly all other primates, remains vulnerable to climate change.
"This is the flip side of what people are worried about now," Beard said, explaining that instead of going from a cooler time to a warmer time, "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."