The Oldest Primate Skeleton

An artistic rendering of Archicebus achilles' skeleton. Grey regions represent the fossilized bones found the specimen. Illustration: Mat Severson, Northern Illinois University

Researchers at Beijing's Chinese Academy of Sciences say the world's oldest known primate is a tiny, 55-million-year-old tree climber dubbed Archicebus achilles. 

A farmer discovered the creature's fossil last year in a quarry near Jingzhou City in central China. The site, now famous for its Eocene-era bird and fish fossils, had been an ancient lake. According to Dr. Xijun Ni, the region had once been covered in lush tropical forests and lakes.

Dr. Dan Gebo of Northern Illinois University says Archicebus is one of the earliest primates ever discovered, and its fossil is the most complete set from the Eocene Era ever recovered.

Archicebus was tiny, weighing under an ounce, with slender limbs and a long tail. Its anatomy was suited to leaping among the trees, feeding primarily upon insects during daylit hours. It seems to have been a hybrid, with the feet of a small monkey, the arms, legs and teeth of a much more primitive primate, and surprisingly tiny eyes.

The creature's name is derived from the Greek words Archi meaning "first" and cebus meaning "long-tailed monkey", while Achilles refers to the legendary Greek warrior with a special heel. This is because its most unusual features are in its feet, which combine strong big toes for grasping, long, nailed toes of ancient tree dwellers and monkey-like heel and metatarsals (innermost toe bones), advanced features not normally found among early Eocene primates. This unique blend of anatomical characteristics places it near the evolutionary split of tarsiers - tiny, nocturnal tree-dwellers - and anthropoids, the lineage which includes modern monkeys, apes, and humans.

Dr. Gebo believes that Archicebus and similar recent discoveries place the origin of primates in Asia, rather than Africa.

Source: Oldest primate skeleton discovered, press release, June 5th, 2013, Northern Illinois University