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Cholesterol helped to name dickinsonia one of the oldest animals

Dickinsonia fossils (Dickinsonia) found in Pomorie
Ilya Bobrovskiy / Australian National University

Paleontologists have found molecular evidence that representatives of the Ediacaran dickinsonia biota Dickinsonia) , which lived 560-555 million years ago, belonged to the animal kingdom. As reported in Science , scientists found in fossil dikinsony cholesterol, a substance that produces animals.

In the Ediacaran period, which lasted from 635 to 542 million years ago, on the planet appeared soft-bodied organisms , most of which, apparently, led a sedentary lifestyle. Some of them were bilaterally symmetrical and looked like feathers or branches of trees. Others looked like disks or bags. A few million years after the start of the next Cambrian period, the Ediacar biota disappeared. Many researchers believe that they were multicellular, and refer to different kingdoms: animals, plants, fungi; others suggest that the representatives of the Ediacaran biota represented the colony of microorganisms.

One of the most famous representatives of the Ediacaran biota was dickinsonia (genus Dickinsonia ), whose fossils were found in Australia and Eurasia. This organism was a corrugated oval body from a few millimeters to 1.4 meters in length and a few millimeters in height. To classify it scientist till now it was not possible: дикинсонию already  considered a mushroom, a plant, a worm, a lichen, a jellyfish, carried to the elementary.

In a new study, Australian, Russian and German paleontologists and biologists decided to check whether dickinsonia was related to lichens, protozoa or animals with the help of biomarkers preserved in fossils. Organisms produce sterol substances that form part of the cell membrane and participate in signaling between cells. There are different in composition of phytosterols, zoosterins and mycosterol – substances that produce plants, animals and fungi, respectively. If you determine the composition of sterols, preserved in fossils of dickinsonia, you can classify it.

The authors studied fossils of two dickinsons, which were found in the whereabouts of Lamitz in Pomerania. Organic matter scientists scraped off fossils, and as control used samples of the rock directly above and under the fossils. The composition of organic substances scientists were determined by means of chromatography-mass spectrometry.

As a result, it turned out that in the control samples the composition of the sterens corresponded to the typical composition of the sterens at the location of Lamitz. 11 percent was cholesterol produced by animals, 15 percent by ergosterol, which, for the most part, forms fungi, and 74 percent is stigmaterin produced by plants. Presumably, this composition is typical for green algae ( Chlorophyta ), which were part of the bacterial mat or inhabited in the water column surrounding dickinsonia. And the composition of the sterens in the fossils of dickinsonium was different. The majority, 93 percent, was cholesterol. This indicates that dickinsonia refers to animals.

This result confirmed the unusual ratio of stereoisomers of sterols. Stereoisomers are substances that are the same in composition but differ in the spatial arrangement of the atoms. In control samples, the ratio of stereoisomers was typical for abiotic isomerization. And in the samples that were scraped off from the fossils of dickinsonia, it corresponded to the values ​​obtained when anaerobic activity of microorganisms, for example, during the decomposition of the corpse.

Previously, researchers based on phylogenetic studies, attributed to animals another Ediacaran organism, Stromatoveris psygmoglena. This organism, in appearance resembling fern leaves or sea feathers, inhabited both the Ediacaran and Cambrian periods, up to 518 million years ago.

 

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