Ancient sea worm leaves fossil burrows – now. Powered by Northrop Grumman

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A recent fossil discovery off the northeastern coast of Taiwan suggests that today’s seaworm has an ancient ancestor lurking in its prehistoric family tree.

In one Nature On paper, researchers examining samples from Miocene strata of the Taiwanese seabed described the discovery of smooth-walled, L-shaped fossil burrows with distinctive feathers around the top. Comparison to today’s strikers suggests his ancestor was also ambush hunting, hiding before exploding up his burrow to snatch unsuspecting fish swimming above his head. Once captured, the prey was dragged deep into the burrow to its fate.

Fossil evidence of an ancient marine worm

Sea worms have soft bodies and they often don’t leave much fossil evidence behind. Instead of skeletal remains, sometimes only their teeth remain. In a 2017 article also published in Nature, scientists reported finding the jaws of giant polychaete worms similar to fossils from Taiwan in Ontario, Canada. Extrapolating from the dimensions of the jaws found, the research team estimated the body size of the worms to be around one meter (just over three feet) long.

In Nature’s most recent publication, there were no worms themselves to examine. Instead, scientists relied on evidence from 319 fossil burrows left by ancient marine worms to draw their conclusions. The team described these fossil traces as being about two meters (over six feet) long and two to three centimeters (about an inch) in diameter. The burrows were L-shaped, with the upper part descending vertically from the ocean floor and then rotating to extend horizontally.

The team noted a distinct feather pattern around the upper shaft, but otherwise the traces had smooth walls. Further examination of the feathering scan of the heart by X-ray fluorescence (XRF) showed a sudden increase in iron deposits around these areas.

Their comparison with modern predatory polychaete worms has helped researchers gain insight into the ancient life of the proposed new ichnogenus, Pennichnus formosae.

Predatory polychaetes hunted by ambush

Based on their fossil evidence, the researchers believe that, like their modern counterparts, P. formosae hunted by ambush. Today’s sand worms, Eunice aphroditois hunt using powerful trap-jawed mouthparts that can split a fish in half. Soft-bodied worms burrow in the sediment of the ocean floor for protection and camouflage. They hide at the entrance to their burrows with their mouthparts barely visible.

Antennas emerge from the burrow both to detect incoming prey and to act as a decoy. Once a fish swims from a distance, the sand hitter launches explosively from its burrow, just far enough to clamp its powerful jaws around its prey. The worm then drags its dinner into its burrow. The quivering of the prey causes the walls of the burrow to collapse again, burying it to its fate. According to Smithsonian, an injection of toxins subdues the prey as the final blow.

Lifestyle secrets of ancient worms

The distinct feathers were a major clue to the identity of the ancient inhabitants of the burrows, as the researchers reported. The lines showed repeated collapses of the sediment walls around the entrance while the iron build-up suggested the damage had been repaired over time.

The explosive ambush tactics of E. aphroditois, followed by their retreat with prey in difficulty, cause the sediment to collapse at the entrance of the burrow. The marine worms then repair the damage, secreting mucus to strengthen the area. Like national Geographical explains that the mucus being rich in organic matter, it attracts the bacteria which colonize the area. As part of their metabolism, certain bacteria often create conditions that lead to local iron deposits.

A long story

In addition to discovering a proposed new species, the results also show that gigantic predatory polychaetes have been exploiting their ecosystem niche for some time. Today’s jawworms, E. aphroditois, can grow up to three meters (almost 10 feet) in length – and also Wired notes, they can also appear in aquariums.

The fossil records of Taiwanese burrows and Canadian mouthparts show that giant worms living on the seabed are not a recent phenomenon. These creatures have been around for millennia, and further exploration of the footprints they have left can help us piece together the biological history of our planet.

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