Computer simulations have allowed scientists to work out how a puzzling 555-million-year-old organism with no known modern relatives fed, revealing that some of the first large, complex organisms on Earth formed ecosystems that were much more complex than previously thought.The international team of researchers from Canada, the UK and the USA, including Dr Imran Rahman from the University of Bristol, studied fossils of an extinct organism called Tribrachidium, which lived in the oceans some 555 million years ago.  Using a computer modelling approach called computational fluid dynamics, they were able to show that Tribrachidium fed by collecting particles suspended in water.  This is called suspension feeding and it had not previously been documented in organisms from this period of time.