For three billion years the Earth was ruled by bacteria, and then, very suddenly occurred Cambrian explosion - and within a few tens of millions of years on the scene burst of multicellular life.

Now gradually becoming clear that this event was in fact preceded by long and careful preparation. Just ediacarian biota (635-540 million years) was mostly spineless, that is, had no such parts, which can easily fossilized, kind of chitin exoskeleton, as in modern insects and crustaceans.


The Image Warren Lucas.

However, samples of Precambrian "armor" still sometimes find it, and the last was found in Paraguay. Organisms, called Corumbella werneri were fixed and predatory inhabitants of the seabed. They had a tubular body, in which the carbon was replaced by minerals, first of all, calcite, which, however, has not prevented the exoskeleton to be organic, and therefore flexible.

"Pipes" are composed of microscopic segments - fused polygonal plates. The latter have holes, sometimes reaching the series, and sometimes arranged by accident. Function "then" is not yet solved. The structure of the plates similar to those that existed at a later organisms that may be associated with some modern jellyfish.

The emergence of skeletons on the basis of calcite can be explained as follows. One of the theories says that this was the result of changes in the chemistry of the ocean, when the concentration of calcium rapidly increased to the current level. Adaptation to new conditions caused the cells to get rid of excess calcium, which led to its accumulation. In the result of natural selection survived those organisms that have calcium deposits led to the formation of protective armour.

Another explanation focuses on the urgent need to have this "armor". Distribution of predators could provoke an evolutionary arms race, and creatures with hard parts had more chances are they will not.

Interestingly, the same sample of the breed also contains an instance Claudine, which has already acquired a skeleton of calcium carbonate. This confirms the second hypothesis, that is, the assumption that the Genesis of the skeleton was associated with increased pressure from predators and the necessity of conquering new niches, and not with geochemical environmental changes that took a low start, by the way, only in the Cambrian.

The study is published in the journal Geology.

Prepared according to Ars Technica.