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World's oldest primate fossil in China sheds light on human evolution

Updated: 2013-06-06
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The world's oldest primate - dating back 55 million years and small enough to fit in the palm of a hand - has been discovered by scientists. 
 
Named Archicebus achilles and smaller than the pygmy mouse lemur, the tiniest living primate, it was unearthed near the Yangtze River in central China. 
 
Even though it weighed under an ounce, the minute animal provides a vital missing link in human evolution. 
 
Its almost complete skeleton marks a pivotal moment on the tree of life when the branch leading to modern monkeys, apes and humans split from that of the nocturnal lemur-like tarsiers of south east Asia. 
 

Named Archicebus achilles and smaller than the pygmy mouse lemur, the tiniest living primate, it was unearthed near the Yangtze River in central China. Even though it weighed under an ounce, the minute animal provides a vital missing link in human evolution
  
Researchers say the new skeleton, which is described in the journal Nature, supports the more recent view that Asia was the continent of origin for primates, not Africa as previously believed. 
  
Small eye sockets reveal it was active by day.
 
Paleontologist Dr Xijun Ni, who led the research, said: 'This region would have been a large series of lakes, surrounded by lush tropical forests during the early Eocene. 
 
'Our analysis shows this new primate was very small and would have weighed less than an ounce. 
 
'It had slender limbs and a long tail, would have been an excellent arboreal leaper, active during the daytime, and mainly fed on insects.' 
 
 
Closest living relatives: the tarsier (L) is considered endangered and only found on islands in South East Asia; the pygmy mouse lemur is the tiniest living primate and is found on the island of Madagascar
  
Tree-dwelling Archicebus would use its chimpanzee-like opposable big toe to cling onto the branches. 
 
Dr Christopher Beard, of the Carnegie Museum of Natural History in Pittsburgh, said: 'Archicebus differs radically from any other primate, living or fossil, known to science. 
 
'It had slender limbs and a long tail, would have been an excellent arboreal leaper, active during the daytime, and mainly fed on insects.' 
 
Tree dwelling Archicebus would use its chimpanzee-like opposable big toe to cling onto the branches. 
 

An artistic reconstruction of Archicebus achilles in its natural habitat of trees in central China
 
Dr Christopher Beard, of the Carnegie Museum of Natural History in Pittsburgh, said: 'Archicebus differs radically from any other primate, living or fossil, known to science.
 
'It looks like an odd hybrid with the feet of a small monkey, the arms, legs and teeth of a very primitive primate, and a primitive skull bearing surprisingly small eyes. 
 
'It will force us to rewrite how the anthropoid lineage evolved.' 
 
The skeleton was digitally reconstructed using state of the art scanning techniques, allowing to establish the fossil was radically different from any other primate, living or extinct. 
 
Anthropologist Dr Dan Gebo, of Northern Illinois University, said: 'This is the oldest primate skeleton of this quality and completeness ever discovered and one of the most primitive primate fossils ever documented. 
 
'The origin of primates sets the first milestone for all primate lineages, including that of humanity. 
 
'Although scientists have found primate teeth, jaws, occasionally skulls or a few limb bones from this time period, none of this evidence is as complete as this new skeleton from China.

'With completeness comes more information and better evidence for the adaptive and evolutionary themes concerning primate evolution. It takes guessing out of the game.' 
 
Dr Ni, of the Chinese Academy of Sciences in Beijing, first came across the fossil years ago while doing fieldwork. 
 
It had been found by a local farmer and was later donated to the university. 
 
It was encased within a rock that was split open to reveal fossils and impressions of the primate on each side of the two halves. 
 
The quarry where it was discovered was once a lake where many ancient fish and bird fossils from the same era known geologically as the Eocene have been dug up. 
 
Dr Ni said: 'Archicebus marks the first time we have a reasonably complete picture of a primate close to the divergence between tarsiers and anthropoids (primates that include monkeys, apes and humans). 
 
'It represents a big step forward in our efforts to chart the course of the earliest phases of primate and human evolution.' 
 
Their study included a three dimensional, high resolution reconstruction, aided by high tech scanning of the fossil at the European Synchrotron Radiation Facility in Grenoble, France.
 
 
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