Oldest Known Animals Had Complex Asexual Lives

The earliest evidence for reproduction in a complex organism had two surprisingly sophisticated modes of reproduction.

The creatures, known as rangeomorphs, lived 565 million years ago in what is now Newfoundland, Canada, according to a study about the find in the journal Nature. The research focused on a particular rangeomorph, called Fractofusus.

"Microscopic multicellular organisms had been around long before the Ediacaran (635–542 million years ago), but it was only during this period that large organisms with complex body arrangements appear in the fossil record," lead author Emily Mitchell told Discovery News.

"The complexity of Fractofusus' reproductive mode is intriguing, in part, because it would be surprising if large complex organisms hadn't existed prior to this development."

While Fractofusus has been considered to be one of the world's first animals, scientists are still not entirely sure what it was.

Mitchell, who is a postdoctoral researcher at the University of Cambridge's Department of Earth Sciences, explained, "Fractofusus looked like nothing that is alive today, and lived in very deep water (1.2 miles below the surface) far below the photic zone, so we know that they were not plants."

On the other hand, "They have no mouths, or any other animal features, nor fungi characters," she added.

For now, Fractofusus is either referred to as being an animal, or as a member of a long-gone clade with no modern counterparts. Remarkably, however, the fossil record is excellent for this ultra ancient creature and other members of its ecosystem. A Pompeii-like volcanic disaster wiped them all out at once, freezing their remains over time.

Mitchell and her team were able to investigate Fractofusus' reproduction by using high-resolution GPS, spatial statistics and modeling to examine how its fossils multiplied and changed on three rock surfaces excavated from the site, which is called Mistaken Point.

They determined that larger "grandparents" of the species were randomly distributed and were surrounded by smaller "parents" and "children." The patterns strongly resemble the biological clustering observed in modern plants, such that the "grandparents" arose from ejected waterborne propagules that drifted along in the current.

The "children" grew from runner-like extensions that were sent out by the older generation. This second form of reproduction is similar to how strawberry plants grow and spread.

Together, both ways of reproducing allowed Fractofusus to reproduce asexually and to cover the sea floor, thereby becoming a dominant presence in its environment. Corals and sponges today use a similar combo technique, coupling release of buds or fragments with production of spores. Certain plants and fungi also engage in comparable forms of reproduction.

Read more at Discovery News