An article published in the journal “Nature Ecology & Evolution” describes the discovery of evidence of the existence of sponges about 630 million years ago, in the Neoproterozoic era. A team of researchers at the University of California, Riverside (UCR) found a biomarker in a fossil dating back to that era called 26-methylstigmastane or just 26-mes that is produced only by sponges. In general, this is the oldest evidence of animal life and therefore multicellular.
The search for fossil biomarkers represents one of the frontiers of paleontology. Organisms that lived in the Ediacaran period or even before leave very little fossil traces and that’s a serious problem in reconstructing the evolution of multicellular organisms and their diversification in the large groups that still exist today. For example, there are some researches that claim that the sponges were the first animals to emerge but there are still no certainties.
In recent years, modern technologies capable of performing highly sophisticated chemical analyzes of sediments that are over 600 million years ago can provide very useful results. That’s because some complex molecules decay but the products of that process can be very stable, so much that they’re still detectable after such long times.
In a research published in the journal “Nature” in February 2009, Professor Gordon Love of UCR had already used a biomarker, a molecule called 24-isopropyl chlorestane or 24-ipc for simplicity, a modified version of cholesterol. Research progressed and again in February 2016 an article published in the journal “Proceedings of the National Academy of Sciences” described one based on 24-ipc.
That biomarker isn’t produced by sponges and therefore the results of research based on it are controversial. For this reason, the team that conducted the research published in 2016 tried to reconstruct the evolution of a gene that produces sterols such as 24-ipc, concluding that the one found in fossil sediments from 640 million years ago was produced by sponges.
To look for more evidence, Professor Gordon Love conducted a new research on fossil sediments discovered in Oman with an age of around 630 million years. This time his team looked for another biomarker called 26-methylstigmastane or just 26-mes, which is produced only by sponges of the demospongiae class, together with 24-ipc. Both biomarkers were detected in the fossil sediments examined and this gave the researchers a greater certainty in their conclusions that they were indeed sponges.
Modern sponges generally produce only one of the two substances, for example Rhabdastrella globostellata produces 26-mes, therefore discovering traces of both in the same sediments represents a further reason of interest and makes it less likely that it’s some isolated or extinct branch of sponges. According to Professor Gordon Love this means that the ability to produce those such unconventional steroids probably emerged very early in their phylogenetic tree, even in the Cryogenian period – 720-635 million years ago – and is now present in a wide range of sponge species.
The publication of this research comes a few weeks after an article published in the journal “Science” that describes an analysis of fossils belonging to the genus Dickinsonia, perhaps the most iconic of the so-called Ediacara biota, based on biomarkers. This type of analysis requires very sophisticated equipment but the results are really interesting.
