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Fossil burrows suggest large worms colonized Eurasian seafloor 20M years ago

Fossil burrows suggest large worms colonized Eurasian seafloor 20M years ago
An illustration shows an ancient predatory worm burrowing in the ocean bottom and snatching an unsuspecting fish with its jaws. Photo by Yu-Yen Pan, et al./Scientific Reports

Jan. 21 (UPI) -- One-of-a-kind fossilized burrows unearthed in Taiwan suggest giant predatory worms colonized the Eurasian seafloor during the Miocene, some 20 million years ago.

Scientists described the novel trace fossils in a new study, published Thursday in the journal Scientific Reports.

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Trace fossils are the holes, pockets and impressions left behind by plants and animals.

These textured cavities and patterned tracks, preserved in ancient rock, don't feature bones or tissue. Instead, they reveal where sea slugs inched across the muddy bottom of an ancient inlet or where the roots of primitive reeds anchored to a prehistoric riverbank.

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Predatory polychaetes, or bristle worms, date to the early Paleozoic, more than 500 million years ago, but because their bodies are mostly soft tissue, their fossil record is spotty.

"Virtually nothing is known about their burrows and behavior beneath the seafloor," researchers wrote in the new paper.

After finding dozens of L-shaped burrows in Miocene deposits located in Tawain, each textured by unique feather-like patterns around the upper shaft, scientists compared the trace fossils to the burrows formed by a modern benthic bristle worm called the Bobbit worm.

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The name of the predatory worm was inspired by the infamous John and Lorena Bobbitt case.

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Also known as the sand striker, the worm, officially Eunice aphroditois, hides quietly in its burrow until unsuspecting prey venture too close. In a flash, the worm erupts from the hole and snatches the prey with its powerful jaws.

According to the new study, the burrows of the Bobbit worm are quite similar to those found in the Miocene rocks recovered from northeast Taiwan, suggesting bristle worms were practicing ambush predation at least 20 million years ago.

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"After 20 [million] years, it's not possible to say whether this was made by an ancestor of the Bobbit worm or another predatory worm that worked in more or less the same way," Ludvig Lowemark, a sedimentologist at National Taiwan University, told The Guardian. "There's huge variation in Bobbit worm behaviour, but this seems very similar to the shallow water worms that reach out, grab fish and pull them down."

In addition to feathery patterning, researchers also found higher concentrations of iron along the upper portion of the burrows.

Scientists suspect the iron was produced by bacteria that fed on mucus deposited by the ancient worms. Invertebrates sometimes secrete mucus to reinforce burrowing structures.

Though the fossils were found in rock deposits in Taiwan, the burrows were originally forged in sediments near the convergence of the Philippine Sea Plate and Eurasian Plate. The tectonic collision began pushing up the land that would form Taiwan around 5 million years ago.

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