

Billion-Year-Old Fossil is a “Missing Link” in Animal Evolution

A very ancient fossil that was found in the Scottish Highlands has provided experts with new information regarding the transformation from single-celled organisms to multicellular creatures. Named Bicellum Brasieri, it is the oldest ever organism found with two cell types and dates back approximately a billion years.

Described as an important “missing link” in the evolution of life, the fossil was discovered at Loch Torridon. The researchers described it as being more complex than just a creature with a single cell (these are called prokaryotes), but it wasn’t fully multicellular. Prokaryotes first showed up on our planet nearly 4 billion years ago.

It is an extraordinarily important piece of the puzzle in the transition from the earliest lifeforms on our planet to today’s creatures – specifically, the gap between the time of single-celled organisms and when the “Cambrian Explosion” happened about 540 million years ago where an evolutionary burst of life occurred on Earth. The time period in between those two events is called the Proterozoic Era.

(Not Bicellum Brasieri)

Professor Charles Wellman from the University of Sheffield and who is an author of the study went into further details, “The origins of complex multicellularity and the origin of animals are considered two of the most important events in the history of life on Earth,” adding that their discovery has provided important information regarding both of those events.

He went on to say, “The discovery of this new fossil suggests to us that the evolution of multicellular animals had occurred at least one billion years ago and that early events prior to the evolution of animals may have occurred in freshwater like lakes rather than the ocean.” It is thought that the organisms that lived at the bottom of lakes are responsible for today’s land plants as well as green algae.

Green algae

Professor Paul Strother from Boston College in Massachusetts and another author of the study weighed in by stating, “Biologists have speculated the origin of animals included the incorporation and repurposing of prior genes that had evolved earlier in unicellular 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 half a billion years later.” Their study was published in Current Biology where it can be read in full.

A picture of the organism can be seen here.

