History of the development of the Mehrzeller begins much earlier

600 million year old fossils show functions of higher multicellular life forms

The 600 million year old fossils show multicellular organisms with surprisingly advanced properties. © Virginia Tech
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How and when did single-celled organisms become multicellular organisms? New fossil discoveries show that 600 million years ago, more highly developed multicellular organisms already existed, as an international team of researchers reported in the magazine "Nature". According to previous assumptions, there were only simple life forms such as bacteria in the oceans of that time. The discovery sheds new light on the developmental history of higher life.

In the earth-historical era of the Cambrian, biodiversity on earth made a giant leap: numerous fossil finds occupy the so-called Cambrian explosion about 540 million years ago. During this time, the ancestors of the largest main groups of today's multicellular animals appeared, including crabs, spiders and the ancestors of the vertebrates, the chordates. However, what happened to this sudden increase, and especially what happened before it, is largely puzzling: how did the single-celled monads, especially cyanobacteria, combine to form multicellular organisms?

60 million years earlier

Geobiologists led by Shuhai Xiao of Virginia Tech University have made a discovery that refutes previous answers to this question: they describe the earliest known ancestor of multicellular animals. Fossil findings from the Doushantuo rock formation in southern China show globular organisms that have distinct characteristics of higher multicellulars - and they date back to around 60 million years before the start of the Cambrian explosion.

The researchers found evidence of tightly connected cells, differentiation in germ cells and body cells as well as programmed cell death. These are clearly evolved characteristics when living things of that time had been awarded so far. In bacteria, these skills do not occur.

No bacteria or algae

The described fossils are extremely well conserved in three dimensions in the rock, so that Xiao and colleagues were able to identify them as embryos of so-called Edicara organisms, which populated the seas some 600 million years ago. Their descent was previously unclear: "Similar fossils like these have been interpreted as bacteria, unicellular eukaryotes, algae or early stages of ancestors of modern animals, " explains Xiao. Now, the Doushantuo fossils can be assigned to the higher multicellular cells in contrast to the unicellular organisms and bacteria previously thought. display

"This opens the possibility for us to shed light on the temporal course and evolutionary steps of multicellular organisms, and how they finally took over the earth in a clearly visible way, " says Xiao. Some previous hypotheses will certainly have to be rejected or revised. In further work, Xiao and colleagues want to explore the developmental stages of the fossils in order to obtain further evidence of their relationship.

(Nature, 2014; doi: 10.1038 / nature13766)

(Virginia Tech, 25.09.2014 - AKR)