Enormous Prehistoric Marine Worms’ Lair Discovered Along Sea Floor

Trace fossils suggest that sand strikers drilled these underground tunnels

A fossil showing a tunnel made by ancient burrowing worms
The worms that burrowed in these tunnels may have been the ancestors of modern Bobbit worms, Eunice aphtoditois, and is the earliest known fossil of an ambush predator Y-Y. Pan ET AL./Scientific Reports 2021

Camouflaged in sandy loam, ancient giant worms waited for unsuspecting prey to swim within their reach and then suddenly emerge from the ground in a snap to pull fish to their demise. Now, 20 million years later, researchers have uncovered these colossal sea predators’ hideaways, according to a study published this month in Scientific Reports. The burrow may be the earliest known fossil of an ambush predator.

The L-shaped lair found imprinted in ancient seafloor sediment from Taiwan measured about 7 feet long and one inch wide, reports Mindy Weisberger for Live Science. The worms that burrowed in these tunnels may have been the ancestors of modern Bobbit worms, Eunice aphtoditois. Bobbit worms or bristle worms have been around since the Cambrian period, reports Live Science, and they can be anywhere between a few inches to 10 feet long. The worms also have sharp teeth, hide within the ocean floor, and use their antenna to sense when prey is nearby. When the Bobbit worm feels something above them, it will lunge out of the sand to snatch and gobble up the ill-fated prey.

The trace fossils were first unearthed in the Yehliu Geopark and Badouzi promontory in Taiwan by accident. Kochi University biologist Masakazu Nara was looking at the rocky sediment for evidence of stingray feeding behavior. Instead, Nara found the secret caves of the ancient sea worms reports, Riley Black for National Geographic.

At first, scientists did not understand what constructed the underground burrows. Many other sea animals like clams, crustaceans, and sea urchins also burrow into the seafloor. From a total of 319 fossil specimens found, scientists saw the worms left a funnel-like structure at the start of the tunnel reports, Helen Thompson for Science News. The strange form hinted towards the animal living within these burrows was violent by nature, with the flared entrance likely a sign of a predator moving in and out of the den, reports Ian Sample for the Guardian.

“It’s not one feature that convinced us this burrow was made by a worm but the combination of features. The funnels indicate a violent event,” paleontologist and study co-author Ludvig Löwemark tells National Geographic.

Researchers also found iron deposits along the top of tunnels’ walls, reports Science News. The iron deposits were most likely leftover from mucus used to reinforce damaged walls after the worms snatched up their prey, says Live Science.

There are no fossilized remains of the worms themselves, however, because finding preserved soft-tissues is rare. The evidence found suggests that if the worms were the ones who made the tunnels, it could be an ancient example of invertebrates hunting vertebrates, reports Science News.

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