Bizarre disc-shaped fossil discovery helps rewrite timeline of Earth animals

10 Dec 2018

Image: © awestound/

An international team of researchers has found substantial evidence that shows life may have been on Earth far longer than we once thought.

Despite being one of the foundations of evolutionary biology, Charles Darwin’s Origin of Species failed to explain the sudden appearance of many different types of complex animals approximately 500m years ago. At the time of writing the famous work, Darwin could only theorise that, for unknown reasons, no records of earlier animals were ever fossilised, or they were just missed by researchers.

Now, an international team of researchers led by scientists from the School of Natural Sciences at NUI Galway has found clear evidence that these ‘pre-fossil’ animals had body tissue incapable of being fossilised. This is the case even in situations where exceptionally well-preserved soft-bodied fossils are known to have formed.

Publishing its findings, the team said that the discovery was made after investigating bizarre disc-shaped creatures called eldonids collected from the Sahara Desert in Morocco. Their anatomy and preservation was examined in NUI Galway and also in labs in the US. This included using the latest geochemical techniques to reveal precisely how different parts of these unusual soft-bodied animals had become fossilised.

The disc-shaped fossil of a eldonid.

One of the fossil eldonids analysed as part of the study. Image: Dr Breandán MacGabhann

A ‘Eureka!’ moment

Dr Breandán MacGabhann, who had first conducted the research as part of his PhD at NUI Galway, described the find in the desert as a “‘Eureka!’ moment”.

He added: “These types of fossils only record and preserve the specific parts of the animals’ bodies which were originally made out of quite complex tissues like chitin and collagen. These body materials are not really present in most primitive animals, like sponges, jellyfish and sea anemones, which of course would have been amongst the first animals to evolve.”

Dr John Murray, who supervised the research project, said the discovery helps confirm a suspicion that scientists have long held but have struggled to prove: that the earliest animal ancestors most likely evolved during a protracted and cryptic time interval, long before more advanced creatures began to become preserved as fossils.

“Our work provides the extra time which Charles Darwin needed to account for the early stages of the evolution of animals, and it solves a seemingly intractable problem which greatly troubled him when he was writing arguably one of the most important books in science,” Murray said.

Colm Gorey was a senior journalist with Silicon Republic