Prehistoric carnivorous marine worms buried under the Pacific Ocean

• Bobbit worms explode from tunnels at the bottom of the ocean to ambush their prey.
• According to a new study, these worms had 2-meter-long carnivorous ancestors that buried themselves in the Pacific Ocean.
• The researchers found tunnels 20 million years old made by these prehistoric worms in Taiwan.
• Visit the Business Insider home page for more stories.

Scientists in Taiwan noticed strange L-shaped burrows in a cluster of rocks eight years ago. As the rocks used to be at the bottom of the Pacific Ocean, they thought the tunnels had been made by shrimp, or perhaps octopuses. But the shape and structure of the dens did not match those made by these creatures, and the mystery endured.

Now, it’s settled: the architects behind the tunnels were worms almost two meters long that lived about 20 million years ago, according to a study published this week. The fossil evidence helped the study’s authors to discover how these predators hunted and built their underwater holes.

According to his research, the ancient marine worms would be waiting under the sand for unsuspecting prey; then, when the fish passed, the worms would jump out of their burrows, trap the swimmers in their open mouths and drag the victims to the bottom of the sea. The collapsed sand around the mouth of the tunnel indicated that the prey was struggling fiercely in the claws of the worms.

The researchers also concluded that the ancient worms are the ancestors of the modern-day bobbit worm, that captures prey in the same way.

Wikimedia Commons

“We knew that predatory worms have existed for hundreds of millions of years, but this is the first time that we can really see evidence of behavior similar to that of modern bobbit worms,” ​​said Ludvig Löwemark, a geoscientist at the National Taiwan University in Taipei and a of the study’s co-authors, said Insider.

Ancient rocks reveal how these huge worms lived

Courtesy of Ludvig Löwemark

The Löwemark group found burrows in layers of sandstone rock in northeastern Taiwan. The rock formed between 5.3 and 23 million years ago, during an era called the Miocene.

They collected hundreds of samples of burrows from the Yehliu Geopark in Taiwan and the Badouzi coast, and then used them to identify the characteristics of fossil remains from prehistoric worm tunnels. A fossil trace is a geological formation left by an animal that does not include the remains of the animal itself.

Courtesy of Ludvig Löwemark

Löwemark and his colleagues think that the specific worms that built the dens they found abandoned them or died. The chance of finding a fossilized worm is very small anyway, said Löwemark, because its soft tissues would decompose quickly after death.

But the remains of fossils can still show how the ancient worm hunted. Scientists named the fossil Pennichnus formosae and determined that the worms built L-shaped burrows about 2.5 centimeters wide and about 2 meters long.

The scientists also found evidence that the sand around the burrows had been disturbed, suggesting that the predator that lived inside moved quickly to ambush the prey, and also that the prey struggled in response.

This is the first time that scientists have found fossil evidence of an ambush predator living under the ocean floor.

“Until now, traces of similar fossils have not been reported anywhere else on Earth,” said Löwemark. Although he added that “this is probably explained by the fact that scientists did not know what to look for until now.”

Courtesy of Ludvig Löwemark

Given that modern bobbit worms hunt in the same way as these prehistoric creatures, the study’s authors raised the hypothesis that they are related.

Other evidence of this idea came in the form of iron found in the rock, towards the upper section of the old dens. When bobbit worms build their dens, they coat them with mucus, and bacteria feed on this mucus, leaving traces of iron. Therefore, the presence of iron in the fossil remains suggests that, like bobbit worms, these ancient creatures sometimes had to reconstruct sections of their burrows with mucus.

An ambush predator

Shahin Dashtgard

Löwemark believes that the worms that built the old dens probably looked a lot like bobbit worms. Bobbit worms, however, can grow up to 3 meters – much more than the 6.5 meter long burrows.

Bobbit worms live in the Atlantic, Indian and Pacific oceans. Only a small portion of their bodies protrudes out of the sand. They dip their antennae into the water, swinging them like tiny worms to attract nearby fish. When the prey approaches, the bobbit worms then explode out of their tunnels, grab the fish with sharp teeth and sink again. The jaw of a bobbit worm, or pharynx, can split a fish in half.

Rickard Zerpe / Wikimedia Commons

According to Löwemark, the prehistoric ancestors of bobbit worms probably had a similar diet. But it is unclear what happens after the bobbit worms take their prey and pull it under the sand (so the digestive process of ancient worms is also a mystery).

Luis Carrera-Parra and Sergio Salazar-Vallejo, ecologists from El Colegio de la Frontera Sur, Mexico, told Wired that they think roundworms bite animals with a narcotic or killer toxin, so the prey “can be ingested” safely – especially if they are larger than the worm – and then digested by the intestine. “

Bobbit worms do not pose a threat to humans, however.