Half-billion-year-old, fern-like animals may be the first social network

Rangeomorphs, fern-like animals from the Ediacaran period, were distinguished, to say the least. In their hey day, these early lifeforms colonized entire sea floors and grew up to two meters tall. They may also have created the first social network on the planet.

New fossil findings offer unprecedented evidence that these organisms, which had no mouths, organs, or means of moving, were connected to one another by thread-like filaments, some of which stretched up to four meters long.

Just like some people can't live without Instagram, these thin filaments may have been critical to the rangeomorphs' survival, involved in everything from nutrition to communication and reproduction.

“It’s this branching architecture that sets rangeomorphs apart from everything else that we know of.”

In a study published Thursday in the journal Current Biology, researchers detail the discovery of these fossilized threads and their potential function for the first time.

“It’s this branching architecture that sets rangeomorphs apart from everything else that we know of,” Frances Dunn, research fellow at the Museum of Natural History and co-author on the new study, tells Inverse.

This is the earliest evidence yet found of life being connected in this way, and may lead scientists to entirely reassess how early organisms interacted with one another.

The fossils come from seven different species of rangeomorph found across 38 separate Canadian sites.

“We need to reassess how we consider community ecology," Dunn says. "What we identify as a single rangeomorph, how we might anticipate these things invading new ecosystems. All of these common questions that we need to rethink," she says.

“It challenges some fundamental assumptions, certainly from my perspective.”

Staying connected

Prior to the Ediacaran period, which took place between 571 and 541 million years ago, all life on Earth was microscopic. This was the key period when the first communities of complex, macroscopic organisms began to appear, and the rangeomorphs seemed to thrive.

"These organisms seem to have been able to quickly colonize the sea floor, and we often see one dominant species on these fossil beds," Alex Liu, a researcher at Cambridge University and co-author on the new study, said in a statement accompanying the research.

"How this happens ecologically has been a longstanding question — these filaments may explain how they were able to do that."

“These rangeomorph communities really are some of the very oldest complex communities of fossils that we find anywhere on earth,” Dunn says. “So they're really quite astounding.”

For years, paleontologists have puzzled over rangeomorphs' weird anatomies. The discovery of the filament networks helps clear up some of these questions about their anatomy and how they managed to survive and thrive in Earth's ancient oceans, Dunn says.

“Rangeomorphs have been something of a paleontological conundrum for a long time, in large part because their body plans are so odd,” she says.

“It's difficult to rationalize them with things that are alive today.”

For years, paleontologists have puzzled over rangeomorphs' weird anatomies. The discovery of the filament networks helps clear up some of these questions about their anatomy and how they managed to survive and thrive in Earth's ancient oceans, Dunn says.

“Rangeomorphs have been something of a paleontological conundrum for a long time, in large part because their body plans are so odd,” she says.

“It's difficult to rationalize them with things that are alive today.”

Funky filaments

The researchers found abundant filament networks between the creatures. Each filament ranged between two and 40 centimeters in length, although some stretched for meters. The filaments varied in density between different locations, ranging from individual strands to hundreds per square meter. Some curled and wound around the different organisms, even doubling back on themselves. Others had branches along their length.

"This branching architecture really is totally unique for most living things," Dunn says.

This structure, of branches within branches, within branches, are called "fractal subdivisions," Dunn says.

Staying so intertwined was likely useful, providing stability against strong ocean currents, and protection. But they could equally have been used for all sorts of things.

One theory is that the filaments allowed the organisms to share nutrients between themselves, after the rangeomorphs absorbed nutrients through the ocean water.

Another is that the tendrils may have been used to reproduce, asexually, with some form of cloning. That’s what some modern algae and many other terrestrial plants, like strawberries, do.

“What this discovery does is it puts not only the idea that rangeomorphs might be clonal back on the table, but it also hints that maybe they might be colonial,” Dunn says. But none of these options are mutually exclusive, and there’s a lot left to find out, she says.

“Following up this study, we want to better understand how these filaments are connecting to specific taxa,” Dunn says.

“More generally, we want to be able to refine the phylogenetic position of rangeomorphs in the animal tree. And if we can do that, then we can better use these characters to help reconstruct animal evolutionary history.”

“As a field we're making great strides towards being able to work out really what rangeomorphs were," she says.

Abstract: Fossils of the Ediacaran macrobiota (571–539 Ma) record phylogenetically diverse marine palaeocommunities, including early animals, which pre-date the ‘‘Cambrian Explosion’’. Benthic forms with a frondose gross morphology, assigned to the morpho groups Rangeomorpha and Frondomorpha/Q9Arboreomorpha, are among the most tempo-rally wide-ranging and environmentally tolerant members of the Ediacaran macrobiota and dominated deep-marine ecosystems 570–560 Ma. Investigations into the morphology, palaeoecology, reproductive strategies, feeding methods, and morphogenesis of frondose taxa together constrain their phylogenetic position to the metazoan (for Rangeomorpha) or eumetazoan (e.g.,Arborea) total groups,but tighter constraint is currently lacking. Here, we describe fossils of abundant filamentous organic structures preserved among frond-dominated fossil assemblages in Newfoundland (Canada). The filaments constitute a prominent component of the eco-systems, and exhibit clear physical associations with at least seven frondose taxa. Individual specimens of one unit terminal rangeomorph taxon appear to be directly connected by filaments across distances of centimeters to meters. Such physical linkages are interpreted to reflect evidence for stolonic connections: a conclusion with potential implications for the phylogenetic placement and palaeoecology offrondose organisms. Consideration of extant stoloniferous organisms suggests that Ediacaran frondosetaxa were likely clonal and resurrects the possibility that they may have been colonial.