How the first complex life reproduced

How one of the first complex lifeforms on Earth reproduced has been unearthed byUK scientists.

For much of Earth's history, life has been dominated by single-celled microbes, which first emerged nearly 4 billion years ago.

Despite this long history, it wasn't until much more recently - within the last 500 million years ago - that complex multi-cellular life began to flourish. Which begs the obvious question, how did these first species reproduce?

Now, Cambridge scientist Emily Mitchell and her colleagues have discovered that one of these primitive species, a flattened, immobile ocean-floor dwelling creature resembling a cross between a slug and a fern.

Growing up to half a metre in length, Fractofusus, as it is known, had no mouth, took in its nutrients through its skin and, the new study shows, had at least two ways of reproducing.

One was to put out runners or "stolons" like strawberry plants, at the end of which would grow a new organism apparently cloned from its parent.

The other reproductive method is to release what the team dub a "propagule" - some kind of spore, or viable fragment of the parent - that is capable of drifting off on the current and taking up residence on a new patch of seafloor.

The researchers made the discovery by analysing a large patch of fossilised seafloor in Newfoundland, Canada, where large assemblages of the creatures, which date to about 565 million years ago, are preserved.

Using a technique called differential GPS, the Cambridge team mapped with high precision the locations of the fossil creatures. Specifically, they were looking how the position of each animal was related to those around it, and the relative sizes of the different organisms in the community.

The distributions of the creatures were clearly not random. Using this data, the researchers, who have presented the findings this week in the journalNature, have been able to show that the largest specimens are distributed in a more haphazard fashion but the smaller associated offshoots cluster around the parent body, with some of these "children" having children of their own.

This strategy would have allowed Fractofusus to colonise propitious local habitats very rapidly, but also spread its wings in search of pastures new.

At the moment, the team cannot tell whether the creatures were reproducing sexually or not.

Nevertheless, according to Mithcell, "The identification in Fractofusus of a multigenerational asexual clonal phase, interspersed with the release of waterborne propagules, is the first statistically robust account of reproductive life history reported in an Ediacaran macrofossil."