Traces of life suggest earlier existence of complex animals, scientists say

Traces of life more than half a billion years old suggest that complex animals evolved millions of years earlier than had been thought.

Scientists discovered burrows made by tiny worm-like creatures the width of a human hair which lived in western Brazil about 550 million years ago.

They are thought to have been among the first organisms capable of muscular movement, but they existed some 10 million years before such complex life forms were previously thought to have appeared on Earth.

Trace fossils depicted using an advanced technique called X-ray microtomography that uses X-rays to create virtual 3D models (The University of Manchester)

Dr Russell Garwood, one of the researchers from the University of Manchester’s School of Earth and Environmental Sciences, said: “This is an especially exciting find due to the age of the rocks.

“These fossils are found in rock layers which actually pre-date the oldest fossils of complex animals – at least that is what all current fossil records would suggest.”

The burrows, which measure less than 50 to 600 micrometres in diameter, were discovered in sediment in the Corumba region of Brazil near the border with Bolivia.

They are classified as “trace fossils” – tracks or burrows left by living organisms rather than remains of bones or body parts.

Trace fossil
Scientists have discovered burrows made by tiny worm-like creatures which lived around 550 million years ago (The University of Manchester)

The animals that made them were similar to the modern roundworm said the scientists, whose findings appear in the journal Nature Ecology & Evolution.

They wriggled their bodies as they moved through the sea-floor mud, leaving the trace fossils behind.

Lead author Luke Parry, from the University of Bristol, said: “Our new fossils show that complex animals with muscle control were around approximately 550 million years ago, and they may have been overlooked previously because they are so tiny.

“The fossils that we describe were made by quite complex animals that we call bilaterians.

Trace fossil
The trace fossils were made by roundworm-like animals that wriggled their bodies through the sea-floor mud (The University of Manchester)

“These are all animals that are more closely related to humans, rather than to simple creatures like jellyfish.

“Most fossils of bilaterian animals are younger, first appearing in the Cambrian period.

“Our discovery highlights an unexplored window for tracking animal evolution in deep time.”

The scientists identified the fossils using an advanced technique called X-ray microtomography that uses X-rays to create virtual 3D models.


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