Old Mattresses
Only a few footprints bear witness to the bizarre organisms that ruled the primordial seas more than 540 million years ago. Whether this enigmatic Ediacaran fauna is one of the forerunners of today's animal world or whether it is more of a lost experiment of nature remains a matter of heated debate. New, surprisingly well-preserved fossils point to beings that are more reminiscent of living air mattresses.
One of the great mysteries of the history of life is the so-called Cambrian explosion: At the beginning of the Cambrian period, around 540 million years ago, a large number of animal life forms appeared out of nowhere. All of today's tribes of the animal kingdom - with the exception of the vertebrates - were suddenly there.
Of course, the species of the Cambrian cannot have arisen out of nothing. As early as 1908, German geologists had discovered fossils of multicellular organisms in Namibia that had lived in the Precambrian, i.e. before the Cambrian. However, their importance was only recognized in the 1940s, when the Australian geologist Reg Sprigg found the remains of sometimes quite bizarre life forms in the Ediacara Hills in South Australia. In the meantime, this Ediacara fauna has been found on almost every continent, showing that numerous species must have felt at home in the seas of the Precambrian.
But are these primeval creatures really among the immediate ancestors of today's animal species? An extremely difficult question, since the few remains of the Ediacara fauna mostly consist of imprints that are difficult to interpret and that cannot be assigned to any modern animal phylum with certainty. Some researchers see them as precursors of jellyfish and worms, others even interpret them as plants or fungi.
The morphology of the new fossils resembles no life form existing today
(Shuhai Xiao) As early as the 1980s, the Tübingen paleontologist Adolf Seilacher expressed serious doubts about the alleged close relationship to today's animal phyla. He interpreted the fossil remains as alien creatures consisting of chambered cavities filled with cytoplasm, resembling quilted air mattresses. According to Seilacher's conviction, it was a separate, completely isolated kingdom of organisms, which he called "Vendobionta".
After twenty years, Seilacher could finally be right. Because the fossils that the researchers around Shuhai Xiao from the Virginia Polytechnic Institute are now presenting are a real stroke of luck: In contrast to other Precambrian fossils, which have been badly affected by time, the remains, which are dated 551 million years, are from the southern China's Dengying Formation surprisingly well preserved. The primeval beings did not have any hard skeletal parts, which would have made life much easier for today's paleontologists. However, after their death, they left cavities in the limestone that filled with calcite crystals, allowing for a three-dimensional reconstruction.
The result was flat, chambered structures that form around a central axis like palm fronds. Seilinger's "living air mattresses" seem to be confirmed. Contrary to Seilinger, however, Xiao and his colleagues believe that the outer chambers of Vendobionta were open and therefore could not have been filled with cytoplasm.
How the old mattresses earned their living remains a mystery. They probably lay on the sediment of Precambrian shallow seas in order to feed on what nature has to offer here. "In any case, the morphology of the new fossils does not resemble any macroscopic life form that exists today," Xiao points out."And at this time, it is still uncertain to what extent the southern China Ediacaran fossils are related to other Ediacaran organisms and to contemporary species."
