It's possible that one of the pivotal events in human evolution occurred around 37 million years ago, when a tiny bug-eating primate the size of a chipmunk journeyed from Asia to Africa by crossing a broad sea that connected the modern-day Atlantic and Indian oceans.
A team of international scientists think they've found evidence of this mighty migration in 14 fossilized teeth uncovered in the Southeast Asian country of Myanmar. The teeth belong to a long-extinct species the scientists have dubbed Afrasia djijidae and who bear a striking resemblance to another ancient primate uncovered in North Africa, Afrotarsius libycus.
You really have to put them under a microscope to figure out any differences, says K. Christopher Beard, a paleontologist with the Carnegie Museum of Natural History and coauthor of a paper on the new find that appeared Monday in the journal Proceedings of the National Academy of Sciences.
Beard says Afrasia djijidae probably resembled a pygmy marmoset, the tiny South American primate also known as a dwarf monkey. Based on the structure of its teeth and the fact that such a tiny primate would need a high-protein diet, the researchers think Afrasia dined on insects and fruit.
While Afrasia appears to be related to fossils found at other Asian sites that are as much as 7 or 8 million years older, scientists haven't been able to find any older relatives of Afrotarsius in Africa -- suggesting that Afrotarsius was a newcomer to the continent, which at that point in history was a large isolated island, like Australia is today.
Because Afrasia and Afrotarsius are from around the same time period and look so similar, that's a clue that the migration happened at that time -- if the migration had happened earlier, the two lineages would likely have diverged more visibly, according to Beard.
Once Afrasia made it to Africa, it found itself without the same kind of competition for resources from other primates that it faced in its homeland. That window of opportunity would allow Afrasia and its descendants to flourish, setting the stage for the evolution of more advanced primates in Africa -- including, perhaps, humans.
Our idea is that the actual colonization of Africa itself probably led to real starburst of evolution, Beard says. These early proto-monkeys won the evolutionary lottery.
One obvious question looms large: How did a rodent-sized primate cross hundreds of miles of ocean? Beard says researchers can only speculate, but it's possible that Afrasia hitched a ride on a floating miniature island.
Sometimes when you have giant hurricanes, the torrential rains can be so heavy that riverbanks will cave off into rivers. If it's a big enough piece of earth so that you've got trees growing out of it and monkeys living in those trees, once it gets washed out to sea, you've got seafaring monkeys, Beard says.
Scientists have seen these floating 'islands' out at sea after big storms and even documented castaway animals hanging on for dear life, according to Beard.