New evidence found in rocks of 540 million years suggest that some of the first animals on Earth were probably ancestors of the Sea sponges Modern.
American researchers Massachusetts Technology Institute (Mit) publish a study on the tracking of fossils Chemicals in old rocks to the ancestors of the sponges modern demos.
The demos are a form of common sponges that were one of the first multicellular animals in evolving, although it is not known exactly when they arose.
The MIT geochemical team identified chemical fossils that could have been left by old sponges in rocks of more than 541 million seniority.
A chemical fossil is a rest of a biomolecule that originated in a living organism and that was buried, transformed and preserved in sediments, sometimes for hundreds of millions of years, MIT explained in a note.
The newly identified chemical fossils are special types of mats, the geologically stable form of sterols, such as cholesterol, found in cell membranes of complex organisms.
The researchers tracked these special mats until, today, the demos, which live in all oceans as soft and fluffy filters, and it is possible that their ancestors shared similar characteristics.
The researcher Roger Summons, of the MIT and one of the signatories of the article, indicates that they do not know exactly how those organism were at that time, but “they certainly lived in the ocean, they had a soft body” and assume that they had no silica skeleton.
The discovery of specific chemical fossils offers “solid evidence that the ancestors of the demos were among the first animals to evolve, and that they probably did it long before the rest of the main groups of animals of the earth,” says the note.
The new study is based on the findings that the group published in 2009, when it identified the first chemical fossils that seemed to come from ancient sponges.
As in their previous work, researchers sought chemical fossils in rocks dating from the building period (the last stage of the Neoproterozoica era) in the east of Siberia, the Saline Basin of the southern Oman and the Bikaner-Nagaur basin, in western India.
In their analysis they sought traces of mats, the geologically stable form of the sterols that are found in all eukaryotes, and found type C31 (with 31 carbon atoms) and C30.
After various tests and lines of research, they found findings that “firmly support” the idea that mats that were found in ancient rocks were produced by living organisms, and not by geological processes.
“We have three lines of evidence that complement and agree with each other and that they point out that these sponges are among the first animals that appeared on Earth,” said Summons.
Now that the team has shown that sterols C30 and C31 are reliable signals of old sponges, plan to look for chemical fossils in old rocks from other regions of the world.
Until now, they can only deduce that sediments and sponges were formed at some point during the building period, but with more samples they will have the opportunity to specify when some of the first animals were formed.