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Tuesday, June 26, 2012

Asian origin of primates



There’s no question that the later stages of human evolution, from about 40 million years ago (mya), took place in Africa. However, primitive primates from before that time have been found in Asia, not in Africa, leading anthropologists to conclude that Asia is the original cradle of all hominins. At some point, early primates migrated from Asia to Africa (quite a trek if you consider that at that time there was a large sea separating the two continents). Researchers from Thailand, Myanmar, France and the U.S., led by Jean-Jacques Jaeger of the Universit√© de Poitiers, discovered a new fossil primate (Afrasia djijidae) that sheds light on when that might have occurred.

The oldest well-documented African anthropoid fossils (Afrotarsius libycus) are found in North Africa and date from 38 to 39 mya. There is no record of primates in Africa from before that time. Meanwhile, A. djijidae was found in Myanmar and dates from about 37 mya. The two creatures are remarkably similar, although the Asian A. djijidae has slightly more primitive teeth. This strongly suggests that primates first arrived on the shores of Africa just under 40 mya. From there, they evolved into a variety of hominins that eventually included Homo sapiens.

Only four A. djijidae upper molars have been discovered thus far, and it took six field seasons of sifting through tons of sediment just to find those. This might not seem like much to go on, but you’d be surprised how much a paleontologist can learn from teeth. The authors give a two-page description detailing every facet and angle of the molars.

Below, you can see fossil molars from the two primates superimposed on a map of the region at that time. Note the Tethys Sea dividing Africa from Eurasia.


Striking morphological resemblance between the right upper molars of the Asian Afrasia djijidae and the contemporaneous African Afrotarsius libycus supports an Asia-to-Africa anthropoid dispersal during the middle Eocene. The regions where the two taxa were discovered are positioned on a paleogeographic map of the Old World during the late Eocene (35 mya).

By the way, the name ‘djijidae’ was chosen in memory of a young girl from the village near where the teeth were found. I think that’s rather nice.