A mouse-sized fossil from China has provided remarkable new insights into the origin of primates.
At 55 million years old, it represents the earliest known member of this broad group of animals that includes humans.
Scientists have called the diminutive creature Archicebus, which roughly translates as “ancient monkey”.
They tell ‘Nature‘ magazine that its skeleton helps explain the branching that occurred at the very base of the primate evolutionary tree.
The team puts Archicebus on the line leading to tarsiers, a collection of small arboreal animals now found exclusively in south-east Asia.
But its great age and primitive features mean it sits right at the base of this lineage, and so Archicebus therefore has much to say also about the emergence of the tarsiers’ sister grouping – the anthropoids, the primates that include monkeys, apes and us.
And it would suggest the first of these anthropoids were, likewise, petite creatures scurrying through the tropical canopies that grew to cover the Earth shortly after the dinosaurs’ extinction.
Artist’s impression: Archicebus lived on a very warm “forest planet”
“We are all very curious about the ancestors of primates, including those of human beings,” said Dr Xijun Ni from the Chinese Academy of Sciences, Beijing, China.
“From this almost complete skeleton, we can conclude that our ancestors were a kind of very small animal. It was very active and agile; and it lived in the trees and fed on insects,” he told BBC News.
The Archicebus fossil is preserved across two slate slabs. Most of the animal’s key bones are recorded, including exquisite impressions of its rear limbs and feet.