Bizarre, three-armed ocean creature shows ancient lifeforms were more complicated than we thought

Ancient sea creatures might’ve been a little more complicated than previously thought, according to new research on the feeding habits of a bizarre three-armed ocean dweller that lived millions of years ago.

Tribrachidium heraldicum hunkered down in shallow sea waters around 555 million years ago, late in the geological period known as the Ediacaran. It apparently looked something like a disk with three fuzzy curving arms, giving it threefold symmetery—as in, each of the three segments were mirror images of the others.

Starfish have fivefold symmetry, and humans have twofold symmetry—if a tall mirror were to be placed between your feet, so that it only reflected half of your body, the reflection would make it appear that you were a whole person. But nothing alive today that we know of has threefold symmetry.

Tribrachidium doesn’t look like any modern species, and so it has been really hard to work out what it was like when it was alive,” explained co-author Dr. Marc Laflamme, an Assistant Professor at the University of Toronto Mississauga, in a statement.

“The application of cutting-edge techniques, such as CT scanning and computational fluid dynamics, allowed us to determine, for the first time, how this long-extinct organism fed.”

Aircraft technology models Tribrachidium body

According to the paper in Science Advances, an international team of researchers from the USA, UK, and Canada used computational fluid dynamics—a technique commonly used when designing aircraft—to build a computer model of the Tribrachidium body and simulate liquid flowing around it.

In the simulation, the currents slowed as they hit the virtual Tribrachidium, and then eddied behind it—which helped bring the water into the nooks of its arms on both the front and back sides. As the water collected in these nooks, food particles settled thanks to gravity, and Tribrachidium was able to eat.

“The computer simulations we ran allowed us to test competing theories for feeding in Tribrachidium,” said Dr. Imran Rahman from the University of Bristol. “This approach has great potential for improving our understanding of many extinct organisms.”

Ancient lifeforms more complex than we thought

In fact, this method has now revealed that ancient lifeforms were much more complex than previously thought.

“For many years, scientists have assumed that Earth’s oldest complex organisms, which lived over half a billion years ago, fed in only one or two different ways,” said Dr. Simon Darroch, an Assistant Professor at Vanderbilt University. These other ways include photoautotrophy (simply put, using sunlight for food).

“Our study has shown this to be untrue, Tribrachidium and perhaps other species were capable of suspension feeding. This demonstrates that, contrary to our expectations, some of the first ecosystems were actually quite complex.”

Suspension feeding “mobilizes organic material that was being carried around in the water column,” said Rahman. Or in other words, organisms feed on food materials suspended in water. “It can increase passage of sunlight through water and potentially increase oxygenation, as well”—helping to clear the water for photoautotrophy.

“This is really exciting, because we didn’t really have any good evidence of suspension feeding in organisms of this time period previously,” Rahman added.


Feature Image: M. Laflamme