Earliest animal ecosystems may have played a role in the evolution of complex life

Earth’s first animals may seem simple compared to present-day species, but they had a considerable impact on the explosion of life on our planet more than half a billion years ago.

The remains of the first marine animal forests from the Ediacaran Period, about 565 million years ago, are revealing how early communities of animal life may have impacted the flow of water. This had knock-on effects on the distribution of nutrients in the deep ocean tens of millions of years before the first fish made an appearance.

To study how these communities affected water flow, researchers created three-dimensional digital models of marine species found on fossil surfaces in Newfoundland, Canada, thereby producing the first virtual communities of Ediacaran animals. These communities were then used in computer simulations of flow, a method called computational fluid dynamics, a technique which is more commonly used in other disciplines such as engineering.

This approach involved placing the digital community inside a virtual flume tank and running simulations of different currents based on the characteristics of the marine environments where these organisms lived.

In the study, published in Current Biology, scientists found that these communities were capable of strongly disturbing the flow of water, both horizontally and vertically in the water column.

Dr Imran Rahman, a Principal Researcher at the Museum and lead author of the study, says, “We know from modern communities that vertical mixing of water is a key process, serving to redistribute heat, nutrients and larvae, and the same may well have been true for the Ediacaran.”

“To address this, we developed a new approach for studying how fossil communities interacted with fluid flow, and this represents a powerful tool for investigating how a wide range of past and present marine ecosystems might interact with their environments.”

What were these marine animal forests like?

The fossils used in this study were found at Mistaken Point in Newfoundland, Canada, a UNESCO World Heritage Site famous for the remains of the earliest marine animal forests. These fossils are preserved exceptionally in life position after they were buried in volcanic ash, making the site a kind of ‘Ediacaran Pompeii’.

Today, marine animal forests include familiar ecosystems such as coral reefs, which support high levels of biodiversity by supplying nutrients, structure and shelter to other organisms.

The fossils from Mistaken Point are made up of multiple branching ‘fronds’ making them appear at first glance more like plants, but recent research suggests they are actually animals. The largest of these stands up to a few tens of centimetres tall. They are thought to have formed dense canopies like an underwater forest. 

These early animals lived in a relatively deep water environment, below the depth to which light can penetrate. They lived on the seafloor, which was likely covered in microbial mats, similar to those found in extreme environments today.

“It would have been a very static environment,” says Imran. “We don’t think things were moving around very much, if at all. All of the fossils we are looking at are thought to have lived in one place throughout their life.”.

Whilst there were no larger animals swimming around as seen in modern oceans, Imran says that doesn’t mean similar processes weren’t occurring.

“Our work suggests that a lot of the ecological functions that we see in present-day marine ecosystems were around at this time,” he explains. 

“These are some of the very first animals that existed, and they are basically influencing the distribution of resources in the same way as occurs today in key marine ecosystems like coral reefs. To me that is amazing because it shows the impact animals were having from their first appearance over 560 million years ago.”

How did these early animal communities impact life on Earth?

The mixing of water is a vital process in the seas today, providing a way for nutrients to be carried and distributed throughout ocean environments. By disrupting water flow, early Ediacaran communities would have impacted the distribution of important resources, including food and oxygen.

This may have had an impact on the animal communities themselves, as slowing the flow of water around them may have enabled them to feed or respire better. But it could also have affected the environment more widely, for example by redistributing nutrients to different parts of the sea floor and thereby making them more habitable for other organisms.

It could also have had an impact by contributing to the oxygenation of the oceans. The resulting increase in the availability of oxygen to animals might have helped them to carry out more complicated modes of life and could have been associated with key innovations such as the evolution of predation.

“The locally enhanced vertical mixing created by some of these Ediacaran communities would have had a major impact on the distribution of important resources in the water column, which could have influenced the evolution of life during this important period,” says Imran.

“The Ediacaran was a critical interval in Earth’s history prior to the Cambrian ‘explosion’ of animals, and perhaps even more fundamental. It saw the first appearance and radiation of large and complex lifeforms, including some of the first animals.”

It also saw the appearance of some entirely new lifestyles and behaviours, as animals became more complex and started interacting with each other. 

“This period was associated with lots of important ecological changes, including the first appearance of animal burrowing, skeletons and predation,” Imrans explains. “These important ecological innovations probably brought about fundamental changes to the Earth’s system and ultimately helped establish the modern animal-dominated biosphere that we see today.”