The 'footprints' of the animal oldest

The researchers have traced signs of molecular animal life in sedimentary rocks of Siberia, India and Oman

Fossils molecular suggest that sponges existed in the deep oceans, 100 million years before the Cambrian period

The first representatives of the animal kingdom inhabited the oceans for over 600 million years ago. Although the impressions their bodies left in the rock provide tangible evidence of their existence, little is yet known of this group of creatures that preceded it beings with complex skeletons solid. Some had oval shape, such as dickinsonia, others had the form of a sheet as the charnias and others were direct predecessors of creatures that exist today, such as the sea sponges. The researchers from the University of Riverside in California just submit the earliest test of animal life, belonging to a sponge that lived between 660 and 635 million years ago. The discovery, published Monday in the journal Nature Ecology & Evolution.

The analysis of sedimentary rocks from southern Oman) has revealed the remains of molecules that produces only one type of sponge (demospongiae), which still exists today. The results confirm that these forms of life existed long before the explosion of multicellular life that occurred in the period of Cambrian, about 530 years, which resulted in the rapid appearance and diversification of complex organisms.

to Find evidence of complex life prior to this explosion is very complicated when you do not have the organic remains visible and the found until now were basically the prints fossilized in sedimentary rocks. But instead of pursuing this type of conventional fossil, the team of the university of california, has tracked signs of molecular animal life -so-called biomarkers - in rocks and oils of Siberia and India, in addition to Oman. So they found a type of steroid produced only by sea sponges, one of the agencies that were among the first forms of animal life.

"The first sponges were probably very small, lacked structure and did not leave a fossil record body easily recognizable", explains Alex Zumberge, a researcher from the University of Riverside and the first author of the article. "So the fossils molecular are key to track to these first animals." In spite of the enormous lapse of time and of all the geological changes that have occurred since then, many of the simple molecules that were once part of the cells of these ancient creatures still linger. "What we do is to look for biomarkers-distinctive and stable to indicate the existence of sponges and other primitive animals".

The large and complex molecules such as DNA or proteins do not survive long after the death of an organism, but the smaller, more stable and yes you can do it. In this case, the biomarker the researchers identified a compound from a steroid called 26-methyl estigmasta (26-month), which has a unique structure synthesized only by certain species of sponges modern, known as demosponjas. "This biomarker is the proof that the demosponjas, and therefore the multicellular animals, thrive in the seas old at least 635 million years," said Zumberge.

Although steroids are often associated with drugs to enhance sports performance, in reality the term refers to a much broader class of chemicals found in the cells of all complex creatures, including animals, protists, and fungi. There are different varieties that can be used to identify the organism that produces it.

In 2009, the same team presented a first paper proving the existence of biomarcadoresde animals of the period neoproterozoico, only that with another steroid, any different, so-called 24-isopropilcolestano (24-ipc). However, in that case, the test was not definitive because the same biomarker is also found in some types of algae. The discovery of the 26-m, which is unique in the demosponjas, means a test more robust on your presence and dating.

"With a record combination of the two markers found in ancient rocks, as they can not be attributed to a branch isolated or a group of demosponjas extinct," said Gordon Love, responsible of the research team. "The ability to produce these steroids probably arose in the deepest of the phylogenetic tree of the demosponjas, although today affecting a wide range of modern varieties".