Until very recently, the oldest known animal that could be seen without a microscope was a prehistoric mollusk that existed 555 million years ago. Now, scientists have discovered traces of fat in a fossil that pushes the timeline back three million more years.

An explosion of life

Around 541 million years ago, life on Earth experienced a massive increase in variety. During a time called the Cambrian Explosion, animals appeared in our fossil records. Before this time, life was limited mostly to single-cell organisms arranged in colonies. The recent discovery of a new fossil that predates the oldest known animal has given scientists pause and made them rethink the whole timeline.


The fossils in question, which have been under scrutiny for the better part of a century, have boggled paleontologists. Debates raged, arguing that these creatures were everything from failed attempts at evolution to giant amoebas. One tiny sample of tissue has finally settled that debate.

Cholesterol says it all

Hiding in the sandstone cliffs of northwestern Russia, fossils of the large Dickinsonia had been boggling the minds of scientists until a Ph.D. student at Australian National University found a specimen containing a trace of ancient cholesterol. The fossilized fat definitively proved once and for all that Dickinsonia was not a four and a half foot single-celled organism, but a very early animal.


Dickinsonia and its brethren belong to a group of life called Ediacaran biota, which predate the Cambrian Explosion by about 9 million years. What does this mean for our timeline of life?

A new definition

Finding such a large specimen prior to the massive onslaught of evolution that marked the beginning of a new epoch has stirred some pots, but the news is exciting.

ZME Science

Ediacaran biota are now the confirmed precursors to the Cambrian Explosion, a discovery which opens the door to new possibilities about the origins of the animal kingdom.