“We’re documenting the oldest case of parasitism in the fossil record,” says Timothy Topper at Northwest University in Xi’an, China. The discovery suggests that the first parasites arose during an unprecedented evolutionary flowering.
About hundreds of fossilised animals evidently covered in creatures that looks like worm are the oldest tangible proof of parasitism, reaching back 512 million years ago when complex animals were still new.
Zhifei Zhang, who is also from Northwest University, has spent years burrowing a quarry in Yunnan province in southern China. The rocks preserved an ecosystem from the Cambrian period. In This era was the first complex animal life, like the first arthropods, which include insects, and echinoderms, which include starfish.
Zhang’s team of reseachers discovered hundreds of fossilised brachiopods. This are basically animals with two shells resembling those of clams and they are called Neobolus wulongqingensis. The soft animal within the shell has a tentacle that generates a water current to suck in food particles. A lot of the brachiopods had objects shaped like tube attached to them: sometimes one or two, but in other cases more than a dozen. These are the fossilised remains of hard tubes that once covered animals. These animals aren’t preserved, but they were most likely worm-like.
it goes without saying these animals lived with the brachiopods, but was it a cooperative relationship where they both gain from each other, or was it a parasitic one? If the worm-like creatures were parasites, brachiopods that hosted them should have been less healthy than those without them.
“We took a whole bunch of measurements of the sizes of the shells of the brachiopods, and those that didn’t have tubes were larger overall.” says team member Luke Strotz.
This suggests that the wormlike creatures were parasites. “This looks like it is a host-parasitic relationship,” says Xiaoya Ma at Yunnan University in Kunming, China, who has once before found evidence of Cambrian parasitism. She says the immense number of animals studied makes the finding “very sound”.
“We also found that the orientation of the tubes all seemed to be consistent, the alignment of the tube preferentially aligns with the feeding intake of the brachiopods.” says Strotz.
This indicates that the worm-like creatures were “kleptoparasites” that stole the brachiopods’ food as it was sucked in by their tentacles. Strotz also claims that they were obligate parasites, meaning that they couldn’t survive without their hosts, but Xiaoya Ma on the other hand, says there isn’t enough evidence. “We don’t know what this tube-dwelling organism is,” says Xiaoya Ma.
It is not clear whether the creatures are some of the first animal parasites, or if there were older examples that haven’t been fossilised. Be that as it may, Topper and Strotz say that a Cambrian origin for parasites would make sense. As well as the appearance of many new animal groups, the era saw animals evolve new behavior pattern, from hunting to burrowing. This may have been as a result of a rise in oxygen levels, which increased animals’ metabolic rates and let them try out new ways of finding food, says Strotz.