Even though some people think they’re disgusting, this Moment of Science is about parasites.
About forty percent of all living species on Earth are parasites. They’re too important to ignore. Besides, in 2020 paleontologists made an important discovery about them. They found the oldest fossil evidence of a parasite ever, in five-hundred-forty million-year-old rocks in Yunnan Province, China. The rocks date to the Cambrian period, when complex life was first appearing on Earth.
Parasites are a common and important part of the modern ecology, and that means they probably were in prehistoric times, too. But parasites are usually small and have soft bodies, so they don’t normally fossilize. But the researchers got lucky. They were studying fossil brachiopods. These are a kind of mollusk—like modern clams and shellfish—that have a hinged shell. This hard shell can be preserved as a fossil. The researchers discovered that some of the shells had tubular structures attached. They think the tubes once housed parasites that used the brachiopods as their hosts.
How could they tell? The researchers studied more than a thousand shells of a particular species of brachiopod, and only a few hundred had the tubes, indicating they weren’t part of the brachiopod’s anatomy. The tubes were always arranged radially so that one end faced the lip of the brachiopod’s clam-shell. The paleontologists think that this was the mouth end of the parasite, and that it intercepted the brachiopod’s food as it was drawn into the lips of the shell.