Fern-like organisms without mouth and organs were among the first multicellular animals on our planet. Now paleontologists have discovered a surprising new property of these beings, who lived 570 to 540 million years ago. Fossil finds from Newfoundland show that these Rangeomorpha may have lived socially: The individual specimens were networked with each other using thin threads. These extensions could have been used for reproduction, but also for the exchange of nutrients, as the researchers suspect. Networking could possibly explain why these fern-like organisms were so dominant and successful at the time.
Life on early Earth remained unicellular and microscopic for more than two billion years. But 570 to 540 million years ago, in the era of the Ediacarium, this suddenly changed. In the primordial oceans, multicellular organisms up to two meters in size spread out – some resembled half-inflated mattresses, others wore scalloped back shells or grew on long stems similar to strange underwater ferns. Despite this plant-like appearance at first glance, these beings showed clear characteristics of animals. However, they still lacked crucial organs, including mouths, stomachs or limbs. Paleontologists therefore assume that the various representatives of this Ediacara fauna feed on osmosis or filtration. From fossil finds there are even first indications of feeding communities and other forms of cooperation. Such conclusions about possible ways of life of these organisms are made more difficult by the fact that they do not resemble any of the large groups of the animal kingdom known today and that they disappeared relatively abruptly at the end of the Ediacarium.
Thousands of filaments between Rangeomorpha fossils
The fern-like Rangeomorpha belonged to the most successful creatures of the Ediacarium. These occurred in various habitats of the primeval deep sea and dominated the ecosystems there. “These organisms were apparently able to colonize the ocean floor very quickly and we often see a species as the dominant species in the fossil beds,” explains Alexander Liu from the University of Cambridge. The appearance of the Rangeomorpha varied from spindle-shaped, rather simple growth forms over lobed or feather-like forms to bush-like creatures with many leaf-like outgrowths. Most of the representatives were anchored to the sea floor, some rose together with their stem-like base one to two meters in height. The Rangeomorpha presumably fed on osmosis – they absorbed nutrients from the surrounding sea water.
The greatest diversity of this group of organisms has so far been found in rock formations on the Canadian island of Newfoundland. The most recent discovery is from there. Liu and his colleague Frances Dunn from the University of Bristol have discovered not only different rangeomorpha and similar leaf-like fossils in almost 40 different finds from the Ediacarium, but they also came across a completely new phenomenon: Many of these creatures seemed to be connected by thin threads to be. “These filaments are typically 100 to 1000 microns thick and two to 40 centimeters long,” the researchers report. “In one specimen, the filament is even 4.10 meters long and ends on the base plate of another conspecific. A second pair of this type lies along a common filament of more than 2.23 meters in length. ”The threads show no traces of cells, grooves or other substructures and at that time appeared to have run on or just below the ocean floor.
Reproduction and nutrient exchange
Overall, Liu and Dunn identified more than a thousand such threads that stretched between the Rangeomorpha. But what was it about? “The filaments are too large to fit known groups of bacteria,” said Liu and Dunn. Their width is also at least an order of magnitude greater than that of modern mushroom hyphae. “As far as we know, there are no fossils or recent filiform organisms that have all of the features we have described,” the researchers state. You therefore assume that these filaments originate from the Rangeomorpha. “The most surprising thing for me was that these beings are connected,” says Liu. “We have always considered them to be individuals, but now we have found that several members of the same species can be linked by these filaments – like a social network in real life.” This could mean that the Rangeomorpha formed a kind of colony.
“The amount of filaments in the Newfoundland finds suggests that these threads were an important and perhaps even integral ecological component of the fern-like Ediacara fauna,” the scientists state. However, this raises the question of what the Rangeomorpha used these filaments for. One possibility would be that they were foothills that served for reproduction – similar to how strawberry plants form offshoots. “If these structures were used only for reproduction, one would expect large specimens to be connected to smaller ones,” say the researchers. But this is by no means always the case, instead individuals of the same size are often connected by threads. Liu and Dunn therefore suspect that the organisms may exchange nutrients via these offshoots. According to the researchers, they could have at least partially compensated for the likely nutrient-poor conditions in this deep-sea habitat. This in turn could explain why the Rangeomorpha in particular have been so successful over large parts of the Ediacarium.
Source: Alexander Liu (University of Cambridge) and Frances Dunn (University of Bristol), Current Biology, doi: 10.1016 / j.cub.2020.01.052