The oldest animals on Earth have formed complex ecological communities

A new analysis highlights the first macroscopic animals on Earth: the enigmatic The biota of Ediacara.

The fossils of Ediacarans have a slightly bizarre appearance that is not shared by any modern animal group. For decades, researchers believed that these enigmatic fossils were ecologically simple. However, by borrowing a method of modern ecology – adjusting species to distributions of relative abundance -, paleontologist Simon AF Darroch of Vanderbilt University and his team learned that these organisms were more like modern animals than we thought.

The analyzes showed that the majority of fossil assemblages are characterized by their ecological complexity. The biota of Ediacara have formed complex communities tens of millions of years before the Cambrian explosion. The creatures lived partially submerged in what was once the bottom of the ocean, some of them being suspended, others filtering the food, others absorbing passively nutrition. Some were even mobile.

Complex communities are those that include species competing for many different resources or species that create niches for others (as in many modern ecosystems). The team has found that the signature of complex communities extends to the earliest fossils of Ediacaran. In other words, as soon as macroscopic life has evolved, it has begun to form various ecological communities, different from those of today.

"The main impact of our work has been to test the simple and complex models of Ediacaran ecosystems," said Darroch, an assistant professor in the Vanderbilt Department of Earth Sciences and Environment.

"Supporting a simple model would suggest that these mysterious organisms were universally primitive, sharing the same basic ecology and all competing for the same resources," he said. "The support for the complex model would rather suggest that they are probably competing for a variety of different resources, just like modern animals.Our analyzes support the complex model, illustrating that – though they may seem odd – these mysterious fossils common with the modern animals we thought. "

Their article, "High ecological complexity of Ediacarans benthic communities", is available online Ecology of nature and evolution.

The team first compiled all fossil data from the published literature on Ediacaran, and then added a set of data collected during fieldwork in southern Namibia. These Namibian fossils are among the youngest in the world and record communities that lived immediately before the start of the Cambrian explosion.

Fossils were one of the few simple communities in the analysis, suggesting that these organisms were ecologically stressed. This supports the idea that the The biota of Ediacara were gradually extinguishing with the approach of the Cambrian explosion. While this is an exciting idea, Darroch said, this is just one data point and it will take a lot more research to prove it.

The team also uses 3D modeling based on the fossil record to better characterize The biota of Ediacara, which completely disappeared 540 million years ago – early arthropods, molluscs and sponges.

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Video: https: //youtu.be/u0Os0qS5utw

Their work is funded by a Smithsonian Institution Peter Buck Postdoctoral Fellowship and a grant from the National Geographic Society (9241-13).