Scientists have used computer simulations to work out how a strange 555-million-year-old creature, with no known modern relatives, ate.

The result, surprising for that time period, reveals that some of the first large organisms formed ecosystems that were much more complex than previously thought, researchers claim.

They studied fossils of an extinct marine organism called Tribrachidium. Using a computer modeling approach called computational fluid dynamics, they concluded that it fed by collecting particles suspended in water.

This is called suspension feeding and it hadn’t previously been documented in organisms from this period.

Tribrachidium lived during a period called the Ediacaran, which ranged from 635 million to 541 million years ago. This period featured a variety of large, complex organisms, most of which are hard to link to any modern species. Another recently studied creature from that era is the ball-like Megaclonophycus.

Scientists previously thought that these organisms formed simple ecosystems characterized by only a few basic feeding methods, said Simon Darroch, a researcher at Vanderbilt University in Nashville, Tenn., and a member of the research team.

The new study, published Nov. 27 in the journal Science Advances, suggests they were capable of more types of feeding.

“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. 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,” said Darroch.

Co-author Marc Laflamme of the University of Toronto Mississauga added: “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. 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.”

Computational fluid dynamics is a method for simulating fluid flows that is commonly used in engineering, for example in aircraft design, but this is among the first applications of the technique in paleontology.

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