Here's What Sex Was Like 565 Million Years Ago

Rangeomorphs dominated the Ediacaran oceans some 565 million years ago. Here’s how they did it.

Aug 3 2015, 3:05pm

Concept drawing of Fractofus. Image: CG Kenchington

Earth's first starter kit of complex lifeforms emerged some 565 million years ago, with a unique group of fractal plant-like animals known as rangeomorphs. These Ediacaran period organisms are considered to be among the first animals—or complex species of any phylum—ever to evolve on our planet.

Now, researchers based out of Cambridge University have discovered that rangeomorphs dominated the ancient oceans using both sexual and asexual reproduction. The new research, published today in Nature, sheds some much needed light on the murky origins of life in our planet's seas.

Fractofusus fossil. Image: AG Liu

"Rangeomorphs don't look like anything else in the fossil record, which is why they're such a mystery," said paleoecologist Emily Mitchell, the paper's lead author, in a statement. "But we've developed a whole new way of looking at them, which has helped us understand them a lot better—most interestingly, how they reproduced."

Mitchell and her colleagues focused on the rangeomorph genus Fractofusus, which is preserved in exquisite detail in southeastern Newfoundland. The team used a novel technique known as the spatial point process to map out the dimensions of the Fractofusus clusters, then they modeled that data.

The results revealed that Fractofusus evolved two means of spreading its rangeomorph glory across the Ediacaran oceans. One strategy was to release waterborne spores to found distant colonies either by sexual or asexual reproduction. Once this "grandparent" generation was established in the new region, the rangeomorphs expanded the colony asexually with new "children" stolons or runners.

Essentially, Fractofusus was sending spores out to seed life in new regions, while also reproducing asexually to take over its local habitat. This reproductive pattern is known as a "nested double Thomas cluster model"—a spatial arrangement similar to that of many modern plant species, such as strawberries.

"The combination of stolon-like reproduction and propagules that we found Fractofusus has is surprisingly common across kingdoms," Mitchell told me over email.

"[L]ots of plants can reproduce in this way, and some species of cnidarians and tunicates can also form clonal colonies via stolon, as well as sexually reproducing," she continued. "Fungi also produce stolon-like filaments called hyphae—these are very different to plants or animals, because two different hyphae network meet they form fruiting bodies (such as mushrooms) which then produce sexual seeds."

"What is unique about Fractofusus is that it is the oldest large organism in the fossil record that has been shown to reproduce in two distinct ways, so could well be the first organism to evolve this common strategy," Mitchell said.

It's no wonder, then, that Fractofusus was so successful during the Ediacaran, given its sophisticated system of founding and bolstering new colonies via two different reproductive modes. Mitchell and her colleagues hope to continue illuminating these longstanding mysteries about the Ediacaran world in the future, using similar spatial analysis techniques to this study.

Spatial point process in action. Image: EG Mitchell

"We are going to extend this analysis to other Ediacaran species to resolve their reproductive modes too," she told me. "We also plan to use spatial analyses to understand how different species interacted with each other and their environment as well as the impact of body size on their interactions."

Slowly but surely, scientists are reconstructing a biosphere that emerged on Earth well over half-a-billion years ago. The species of the Ediacaran age may seem completely alien to us now, but they are the foundational lifeforms of our modern global ecosystem. Studying their lives and times contextualizes all that came after.