Wednesday, November 29, 2023

Is this a fossilized lair of the terrible Bobbit worm?

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Not too much my own horn, but I know a thing or of them about weird animals. And I can tell you without a doubt that the bobbit worm is by far the most bizarre. More and more 10 feet long, the worm digs a burrow in the seabed, leaving only its bear trap with a protruding mouth. When a fish approaches, the bobbit worm comes out of its burrow at an astonishing speed, snapping its jaws around its prey. With violent tugs, the worm then drags the victim into its den, where it eats the live fish. (Oh, there is video.)

Now, scientists say they have found evidence that an ancestor of the bobbit worm may have threatened fish 20 million years ago. Writing today in the newspaper Scientific reports, researchers argue that hundreds of fossilized worm burrows, found in what is now Taiwan, are showing telltale signs of struggle. They haven’t found the worms themselves, you notice, as boneless creatures like worms (called invertebrates because they don’t have backbones) very rarely fossilize. Instead, they discovered trace fossils, geological features that suggest the behavior of ancient animals, in the sandstone that was once a seabed.

“This is, in our opinion, the first time that we have found a trace of a fossil that shows how invertebrates like worms fed on vertebrates,” said Ludvig Löwemark, sedimentologist at National Taiwan University, co-author of the new article. “Because, generally, what we find in the sediment archives are animals that move in the sediment. Invertebrates, for example, can tunnel through the seabed and pump water through their burrows, filtering out particles. “But this is the result of a much more active behavior,” he continues. “The worms were actually hiding in the sediment, jumping, grabbing their prey, and then dragging that prey into the sediment.”

The sandstone formation in Taiwan, where giant worms once hunted.

Courtesy of Ludvig Löwemark

Fossilized burrows are approximately 6.5 feet long. From their openings on the surface of the seabed, they would have sunk more or less directly into the mud. Then, halfway down, they would bend about 45 degrees, creating the shape of an L or a boomerang. Near the tunnel entrances, Löwemark and his colleagues noticed “collapse funnels,” or piles of sediment that had accumulated inside the burrow. Researchers say it’s a sign of struggle, preserved for millions of years in the fossil record: As a worm dragged a squirming fish into its lair, sediment poured out to fill the empty.

A cross section of a burrow is shaped much like a feather, the main channel being the well, and the collapse funnels branching into the sediment on either side. Researchers say this is a hallmark of the worms’ eating habits. “When the worm has digested its prey, it reappears on the surface,” Löwemark explains. “He reestablishes a tunnel system in the middle of these collapsing structures, and that’s how these feather-like structures around the tube are formed.”


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