The first organisms on Earth were single-celled organisms similar to what we know as modern Archaea. But what did the first animals look like? The first ‘proto-animals’ were known as rangeomorphs and lived during the Ediacaran period, but not much has been known about how they lived. A new study was able to reconstruct these early animals, providing new insight into these creatures. The research was led by Jennifer Hoyal Cuthill of the University of Cambridge and the paper was published in the Proceedings of the National Academy of Sciences. 

Though multicellular life appeared hundreds of thousands of years before rangeomorphs lived between 635 and 541 million years ago, most of it was incredibly small. Rangeomorphs looked a lot like ferns, with fractal branches along their bodies. They were quite variable in size, ranging anywhere from 10 centimeters to 2 meters.

There was a time when it wasn’t clear whether rangeomorphs were actually animals, or if they were plants. Through much study and debate, it was resolved that they were animals. Their soft bodies left fossilized imprints in rocks, but scientists had been previously unable to discern much about their growth or their eating and reproductive habits. However, Hoyal Cuthill’s team was able to use these imprints to develop 3D renderings and study their life habits.

“We know that rangeomorphs lived too deep in the ocean for them to get their energy through photosynthesis as plants do,” Hoyal Cuthill said in a press release. “It’s more likely that they absorbed nutrients directly from the sea water through the surface of their body. It would be difficult in the modern world for such large animals to survive only on dissolved nutrients.” 

The branched bodies of rangeomorphs increased the amount of surface area exposed to the ocean water, allowing them to take up nutrients, carbon, and oxygen. As they were the extent of animal life at the time, they did not have to compete for resources, and were able to flourish for over 100,000 years. 

However, things quickly went downhill for the rangeomorphs at the onset of the Cambrian Explosion roughly 542 million years ago. Over a period of about 30 million years (relatively slow, evolutionarily speaking), a series of changes within the environment and within the organisms brought about an explosive amount of diversification of life. With so many novel species fighting to survive, it was an extreme evolutionary arms race. 

Animals that developed more sophisticated ways to eat, including eating other animals, were deftly able to out-compete the rangeomorphs that were immobile and had no defense mechanisms. Eventually, they were driven to extinction. Still, a 94-million-year run is nothing to sneeze at.

“As the Cambrian began, these Ediacaran specialists could no longer survive, and nothing quite like them has been seen again,” Hoyal Cuthill concluded.

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