These tube-shaped creatures may be the earliest known parasites
Tube-dwelling creatures that spent their lives cemented to the shells of clamlike brachiopods over 500 million years ago may be the earliest known parasites. “Parasitism is an integral part of life on Earth, but it’s been hard to determine when it emerged,” says Tommy Leung, a parasitologist at the University of New England in Armidale, Australia. But, he says, it likely arose early, in part because today “practically every living thing has some kind of parasitic thing living on or in them, even down to parasites themselves.” Sometimes, scientists get lucky and find parasites preserved with their hosts in amber (SN: 12/10/19). But usually parasites don’t fossilize well because their bodies are often small and soft, Leung says. And even if two organisms happen to be entombed in the same fossil, it can be difficult to discern whether their relationship was parasitic, mutualistic or somewhere in between. Fossils of tongue worms from 425 million years ago represent a clear early example of parasitism, but previously...