Clearest picture yet of oldest primate

05 June 2013

Scientists have got the clearest picture yet of one of the oldest primate ancestors. A remarkable fossil reveals the majority of the skeleton of an animal small enough to fit in the palm of your hand that lived 55 million years ago.

A team led by Xijun Ni of the Chinese Academy of Sciences, Beijing, China, reports details of the oldest near-complete primate skeleton this week in the journal Nature.

The fossil skeleton of Archicebus achilles was unearthed in Hubei Province, China, and dated to very early in the Eocene Epoch.

Archicebus, which roughly means 'ancient monkey', had large eyes, hunted insects, lived in the trees, and was active during the day.

Archicebus is one of the earliest known primates, the group that we, Homo sapiens, belong to, and its age suggests that the last common ancestor we shared with it occurred earlier than previously thought.

Remarkable fossil
55-million-year-old primate skeleton Archicebus achilles

55-million-year-old primate skeleton Archicebus achilles unearthed in China. The bones are articulated, or joined together, which makes them extremely valuable scientifically. © Paul Tafforeau/ESRF and Xijun Ni/Chinese Academy of Sciences

The fossil skeleton is important because much of it is preserved articulated, with the bones joined together as they were in life.

Natural History Museum fossil mammal expert Dr Jerry Hooker comments on the finding, 'Archicebus achilles is remarkable for being the oldest articulated skeleton of a primate to be found'.

'It is also the oldest skeleton of a haplorhine, a subgroup of primates, to which tarsiers, monkeys, apes and humans belong'. 

This group differentiated into Tarsiiformes, which includes the enormous-eyed small tarsiers from Southeast Asia and of which Archicebus is a primitive relative, and Anthropoids, the monkeys, apes and humans. The team says this new research shows this split occurred earlier than previously thought.

Archicebus' skeleton displays haplorhine characters, such as the structure of the ankle joint, and tarsier features such as long toes. Its typically primate heel bone has certain unique features, which is why it was given the species name 'achilles'.

Hooker adds, 'Its limb structure, particularly the mobility of the elbow and the foot, long hind legs and an opposable big toe, allows interpretation of its locomotion as grasp-leaping'.

Other primate fossils

The oldest ever fossil primate finds date from within a million years of Archicebus says Hooker. These are pieces of skeleton found disarticulated (separated at the joints) and date to 56 million years ago.

Hooker explains, 'Most mammal fossils, including those of primates, are fragmentary, usually consisting of isolated teeth or jaws, sometimes also other skeletal elements, and we have learned a lot from these.

'To have a 50% complete articulated skeleton of a primitive primate is much more instructive in terms of estimating lifestyle and relationships'.

‘In fact, in terms of the most important bones from the point of view of understanding relationships and mode of life, Archicebus' is more like 70-80% complete.’

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