The exact moment when a 550 million year old cell began to
divide has been captured in an exquisite 3-D image.
The picture is one of a series taken by researchers examining
ancient fossil embryos from Guizhou Province, China.
The specimens, described in the journal Science, are the oldest
known examples of fossil embryos, and shed light on the early
evolution of complex life.
Scientists used an advanced X-ray technique to peer inside the
balls of cells to reveal the structures inside.
"We have been able to tease apart every structure, geological or
biological," said Professor Phil Donoghue of the University of
Bristol in the UK and one of the team who worked on the 162 pristine
The tiny fossils are part of the Doushantuo Formation in South
China, a limestone bed deposited between 635 and 551 million years
ago that contains layers composed almost entirely of fossil embryos.
The team behind the research believe the fossils are the
developing offspring of extremely primitive sponge-like creatures.
To resolve the delicate internal structures, the scientists used
a technique known as microfocus x-ray computed tomography (microCT).
The method allowed the team to construct 3-D images of the tiny
Computer software was then used to analyse individual cells.
"We digitally extracted each cell from the embryos and then
looked inside the cells," said Shuhai Xiao of Virginia Tech
University in the US.
Inside, the team found kidney-shaped structures which they
believe could be nuclei or other subcellular components.
"It is amazing that such delicate biological structures can be
preserved in such an ancient deposit," said Professor Xiao.
In some four-celled embryos, each cell had two of the
kidney-shaped structures, suggesting they were caught in the process
of splitting prior to cell division.
Explosion of life
Although the bed is packed full of the tiny fossils, the team
has been unable to find any adult specimens.
Previous research has suggested that the embryos were the
product of complex animals, the ancestors of modern organisms.