A new perspective on animal evolution

Traces of trench on the sea floor of giant single-celled creatures in deep water can bring new insights into the evolutionary origin of animals, Mikhail biologist "Misha" Matz, of the University of Texas in Austin, said.

Matz and colleagues recently discovered grape-sized unicellular organisms and their complex traces on the seafront near the Bahamas. This is the first time that unicellular organisms have been discovered to leave traces like animals.

This finding is significant, because similar fossil trenches are found dating back to prehistoric times, about 1.8 billion years ago , thought to be of multicellular animals.

Matz, a professor of biology, said: 'If giant unicellular organisms appear 600 million years ago and their traces are fossilized, a paleontologist today will surely assume that trace. belongs to a symmetric multicellular animal. Now we have to reconsider the fossil record '.

The team's findings are published in the online journal Current Biology.

Most animals, from humans to the back, have a symmetrical shape on both sides, meaning that they can be divided into two halves in the same way.

Bilateral animals, or 'Bilateria', appeared in the fossil record of the Cambrian century 542 million years ago, quickly developing into the main groups or fauna that still exist today. This rapid diversification, known as the Cambrian explosion, makes Charles Darwin difficult to understand and remains one of the biggest questions about animal evolution to this day.

Very few fossils existed could be the original ancestors of symmetrical animals on both sides, and there is still much controversy surrounding these fossils. Fossil traces are the most widely accepted evidence of the existence of these primitive animals.

Matz explained: 'We often assume that a symmetrical body is needed to move in one direction along the seabed and thus leave a trace. Now, we see that unicellular organisms can leave traces with similar complexity and shape. '

The giant unicellular creature, Gromia sphaerica, approaches the coral that grows on a sea urchin. ( Photo: Dr. Mikhail Matz, University of Texas, Austin)

With this finding, Matz and colleagues argue that fossil tracks cannot be used as the only evidence to prove that multicellular animals evolved from primitive times, preparing for the boom period in Cambrian century.

Matz said: 'I personally think that the original period was completely the reign of single-celled organisms. Our observations open a new way to analyze fossil records from the primitive time. '

He said the emergence of all animal body shapes in the Cambrian explosion is not just an artifact of fossil record. It is possible that other mechanisms exist to explain the explosive origin of multicellular living forms.

DNA analysis confirms that the giant single-celled organism found by the Matz and colleagues in the Bahamas is Gromia sphaerica, which was previously known to have originated in the Arabian Sea.

They did not observe this giant single-celled creature in action, and Matz said they moved very slowly. The specimen on the seabed is very stable and there is no perfect condition for preserving these traces.

Matz says unicellular organisms move by pushing leg-like tendons, called pseudopodia, from outside the cell in many directions. Pseudopodia then clings on the flare in one direction and the creature rolls in that direction and lays the trace.

He plans to return to the site in the future to observe their movements and study other traces on the seabed.

The bubble-like body shape of this giant single-celled organism is one of the oldest macroscopic structures on the planet, dating from 1.8 billion years ago.

Matz said: 'These guys are the last living fossils of the macro world'.