Chinese fossils shed light on the evolutionary origin of animals from single-cell ancestors

December 22, 2011

All life evolved from a single-celled universal common ancestor, and at various times in Earth history, single-celled organisms threw their lot in with each other to become larger and multicellular, resulting, for instance, in the riotous diversity of animals. However, fossil evidence of these major evolutionary transitions is extremely rare.

The fossils, reported this week in Science, preserve stages in the life cycle of an amoeba-like organism dividing in asexual cycles, first to produce two cells, then four, eight, 16, 32 and so on, ultimately resulting in hundreds of thousands of spore-like cells that were then released to start the cycle over again. The pattern of cell division is so similar to the early stages of animal (including human) embryology that until now they were thought to represent the embryos of the earliest animals.

The researchers studied the microscopic fossils using high energy X-rays at the Swiss Light Source in Switzerland, revealing the organisation of the cells within their protective cyst walls. The organisms should not have been fossilized - they were just gooey clusters of cells - but they were buried in sediments rich in phosphate that impregnated the cell walls and turned them to stone.

Lead author Therese Huldtgren said: "The fossils are so amazing that even their nuclei have been preserved."

Co-author Dr John Cunningham said: "We used a particle accelerator called a synchrotron as our X-ray source. It allowed us to make a perfect computer model of the fossil that we could cut up in any way that we wanted, but without damaging the fossil in any way. We would never have been able to study the fossils otherwise!"

This X-ray microscopy revealed that the fossils had features that multicellular embryos do not, and this led the researchers to the conclusion that the fossils were neither animals nor embryos but rather the reproductive spore bodies of single-celled ancestors of animals.

Professor Philip Donoghue said: "We were very surprised by our results - we've been convinced for so long that these fossils represented the embryos of the earliest animals - much of what has been written about the fossils for the last ten years is flat wrong. Our colleagues are not going to like the result."

Professor Stefan Bengtson said: "These fossils force us to rethink our ideas of how animals learned to make large bodies out of cells."
This release is available in Swedish.The research was funded by the Natural Environment Research Council, the Swedish Research Council, the Paul Scherrer Institut, Ministry of Science and Technology of China, National Natural Science Foundation of China, and EU FP7.

Notes to editors


Huldtgren, T., Cunningham, J. A., Yin, C., Stampanoni, M., Marone, F., Donoghue, P. C. J. and Bengtson, S. 2011. 'Fossilized nuclei and germination structures identify Ediacaran "animal embryos" as encysting protists' in Science 334.

Therese Huldtgren is a doctoral student at the Department of Palaeozoology, Swedish Museum of Natural History, and Stockholm University, Stockholm, Sweden.

Dr John Cunningham is a Research Associate at the School of Earth Sciences, University of Bristol, UK.

Professor Chongyu Yin is a Researcher at the Institute of Geology, Chinese Academy of Geological Sciences, Beijing, China.

Professor Marco Stampanoni is Head of X-ray Tomography at the Paul Scherrer Institute, Villigen, Switzerland and Assistant Professor for X-ray Microscopy at the Department for Information Technology and Electrical Engineering of ETH Zürich, and Institute of Biomedical Engineering of the University of Zürich and ETH Zürich.

Dr Federica Marone is a beamline scientist at the Paul Scherrer Institute, Villigen, Switzerland.

Professor Philip Donoghue is Professor of Palaeobiology in the School of Earth Sciences, University of Bristol, UK

Professor Stefan Bengtson is Professor of Palaeozoology, Swedish Museum of Natural History, Stockholm, Sweden

Issued by the Public Relations Office, Communications Division, University of Bristol, tel: 0117-928-8896, email:

University of Bristol

Related Fossil Articles from Brightsurf:

Fossil shark turns in to mystery pterosaur
Lead author of the project, University of Portsmouth PhD student Roy Smith, discovered the mystery creature amongst fossil collections housed in the Sedgwick Museum of Cambridge and the Booth Museum at Brighton that were assembled when phosphate mining was at its peak in the English Fens between 1851 and 1900.

New fossil seal species rewrites history
An international team of biologists, led by Monash University, has discovered a new species of extinct monk seal from the Southern Hemisphere -- describing it as the biggest breakthrough in seal evolution in 70 years.

How to fix the movement for fossil fuel divestment
Bankers and environmentalists alike are increasingly calling for capital markets to play a bigger role in the war on carbon.

New fossil ape is discovered in India
A 13-million-year-old fossil unearthed in northern India comes from a newly discovered ape, the earliest known ancestor of the modern-day gibbon.

Fossil growth reveals insights into the climate
Panthasaurus maleriensis is an ancestor of today's amphibians and has been considered the most puzzling representative of the Metoposauridae.

Australian fossil reveals new plant species
Fresh examination of an Australian fossil -- believed to be among the earliest plants on Earth -- has revealed evidence of a new plant species that existed in Australia more than 359 Million years ago.

Tracking fossil fuel emissions with carbon-14
Researchers from NOAA and the University of Colorado have devised a breakthrough method for estimating national emissions of carbon dioxide from fossil fuels using ambient air samples and a well-known isotope of carbon that scientists have relied on for decades to date archaeological sites.

Rare lizard fossil preserved in amber
The tiny forefoot of a lizard of the genus Anolis was trapped in amber about 15 to 20 million years ago.

Reconstructing the diet of fossil vertebrates
Paleodietary studies of the fossil record are impeded by a lack of reliable and unequivocal tracers.

Fossil is the oldest-known scorpion
Scientists studying fossils collected 35 years ago have identified them as the oldest-known scorpion species, a prehistoric animal from about 437 million years ago.

Read More: Fossil News and Fossil Current Events is a participant in the Amazon Services LLC Associates Program, an affiliate advertising program designed to provide a means for sites to earn advertising fees by advertising and linking to