Ancient Penis Worms Commandeered Shells for Self-Defense, Fossils Show

Hermit crabs transfer into different animals’ discarded shells as shelter, as a result of the ocean is a treacherous place, stuffed with hungry predators. Half a billion years in the past, one other creature developed the identical defensive technique, suggests new fossil proof.

But this was no crab. It was a penis worm—an animal that appears exactly the way you’d anticipate.

Penis worms are cylindrical, invertebrate animals discovered within the phylum Priapulida, they usually typically do resemble their genital namesakes, however the similarities cease on the common form. Unlike penises (fortunately), priapulids have an extensible proboscis and a robust, everting throat lined with sharp enamel. These days, they dwell humble lives burrowing into sediment, feeding on detritus or capturing small invertebrates. But penis worms have a deep evolutionary historical past, stretching again over 500 million years, shortly after an occasion the place animal life skilled an unimaginable burst of physique plan evolution and variety (the “Cambrian Explosion”).

It was from this time interval that 4 unusual fossils emerged from rock in japanese Yunnan Province, China, found by a staff of researchers at Yunnan University in Kunming. The fossils gave the impression to be penis worms within the historical Eximipriapulus genus, however their our bodies had been intently overlapping with the stays of conical shells.

“It’s not immediately obvious what’s happening, it takes a little bit of careful interpretation,” mentioned Martin Smith, a paleontologist at Durham University within the U.Okay. who collaborated with the Yunnan University staff.

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Close inspection of the fossils revealed a remarkable window into ecosystems in the deep past. The worms—only a smidge longer than a fingernail—seem to be using empty shells found in their environment as permanent shelters, the researchers report in a new paper in Current Biology.

Alternative explanations, like the worms using the shells as temporary shelters for molting or egg laying, aren’t as likely, the researchers argue. The worms so closely match their funnel-shaped accommodations in size that the shells were probably carefully selected, much like a hermit crab’s relationship with a shell.

The worm was probably ‘hermiting’ in a similar manner, hiding out from predators and looking like an anxious, uncooked sausage stuffed in a traffic cone. “Defense really is the reasonable explanation,” mentioned Smith.

No living priapulid worm is known to behave like this, and neither is any animal from this early in the fossil record. Hermiting has evolved multiple times in different animal groups, but the worms predate some of the first known examples of the strategy by around 300 million years. They’re so old that the animals whose shells they’re using—hyoliths—have been extinct for hundreds of millions of years.

The discovery provides to rising proof that penis worms was fairly a bit extra various of their habits. Scientists already knew, for example, that some priapulids had been significantly fearsome, performing as flesh-rending predators of their historical ecosystems.

The finding also paints a picture of ocean ecosystems shortly after the Cambrian Explosion that is very different from what has largely been assumed by researchers, according to Smith. Predators and the adaptations prey animals use to evade them were thought to be fairly low-key compared to the ocean ecosystems that came later.

But if the penis worms were seeking protection, something back then was probably trying to eat them.

“Maybe the Cambrian was actually quite a nasty place, a dangerous place” said Smith, noting that carnivorous arthropods and their creepy, shrimp-mustached relatives prowled Cambrian seas.

Half a billion years in the past, animal-rich ecosystems not that completely different from as we speak’s could have burst onto the scene, relatively than slowly creating over lots of of tens of millions of years.

“This is an important find,” said Ben Slater, a paleobiologist at Uppsala University in Sweden not involved with this research, adding that the discovery “demonstrates that while the species and animal groups that dominated Cambrian ecosystems were very different, they interacted in very familiar ways: in other words, different actors following the same script.”

Sarah Jacquet, a paleontologist at the University of Missouri in Columbia also not involved with the new paper, said the hermiting behavior may be enshrined in the fossil record more than scientists have yet detected, “but the chance of preserving it is extremely low.”

She famous that the findings may steer researchers in the direction of re-evaluating fossils of different historical shelled species to see if any creatures carrying the armor have been inadvertently ignored.