A billion-year-old fossil has been discovered in the Scottish Highlands, providing a new link in the evolution of animals.
A team of scientists, led by the University of Sheffield (UK) and Boston College (USA), has found a microfossil containing two different cell types and could be the first multicellular animal ever recorded.
The fossil reveals new insight into the transition from single-celled organisms to complex multicellular animals. Modern holozoans are the most primitive living animals, but the discovered fossil shows an organism that falls somewhere between unicellular and multicellular animals.
The fossil has been formally described and named Bicellum Brasieri in a new research paper published in Current Biology.
Professor Charles Wellman, one of the principal investigators, from the Department of Animal and Plant Sciences, University of Sheffield, said:The origins of complex multicellularity and the origin of animals are considered two of the most important events in history of life on Earth, our discovery sheds new light on both .
We have found a primitive spherical organism formed by an arrangement of two different cell types, the first step towards a complex multicellular structure, something that has never been described before in the fossil record .
The discovery of this new fossil suggests that the evolution of multicellular animals occurred at least a billion years ago and that the earliest events prior to the evolution of animals may have occurred in freshwater such as lakes, in place of in the ocean .
Professor Paul Strother, principal investigator at Boston College, said:Biologists have speculated that the origin of animals included the incorporation and reuse of earlier genes that had evolved earlier in single-celled organisms .
What we see in Bicellum is an example of such a genetic system, involving cell-cell adhesion and cell differentiation that may have been incorporated into the animal genome 500 million years later .
The fossil was found in Torridon Firth in the northwestern Scottish Highlands. Scientists were able to study the fossil thanks to its exceptional preservation, which allowed them to analyze it at the cellular and subcellular level.
The team now hopes to examine the Torridon sites for more interesting fossils that may shed more light on the evolution of multicellular organisms.