Giant Worms May Have Burst From Seafloor Burrows to Prey on Prehistoric Fish

Scientists recently uncovered the ancient dens of 2-meter-long worms.
Image of cliffs by the seashore, where fossilized burrows from an ancient worm were found.

At this site in northeast Taiwan, researchers found fossils of burrows that were made by large worms about 20 million years ago.

Media credits

National Taiwan University

Charles Q. Choi, Contributor

(Inside Science) -- Giant worms that exploded upward from the seafloor to ambush unsuspecting prey may have once laired in the waters near Eurasia about 20 million years ago, a new study finds.

Scientists analyzed what appeared to be 319 L-shaped burrows preserved within sandstone formations in the remains of an ancient seafloor in northeast Taiwan. They suspected these were trace fossils -- fossils that are not part of an organism's body, but instead something it leaves behind, like footprints.

These fossils are up to roughly 2 meters long and 2 to 3 centimeters wide. The shape of these burrows suggest they were once the lairs of giant predatory marine worms similar, according to researchers, to the modern Bobbitt worm (Eunice aphroditois), a name taken from the infamous John and Lorena Bobbitt case. These predators, which can grow up to 3 meters long, hide in long narrow burrows within the seafloor in order to grab prey in their powerful jaws.

The scientists named the species behind these trace fossils Pennichnus formosae. "Penna" is Latin for feather, after plumelike structures found around the upper part of these burrows, which the researchers suggest were likely caused by collapsing sediment as these worms dragged prey into their dens. "Ichnus" is Latin for trace. "Formosa" is Latin for beautiful, and also the old Portuguese name for Taiwan, explained study co-author Ludvig Löwemark, a sedimentologist at National Taiwan University in Taipei.

The scientists also found high concentrations of iron toward the tops of the burrows. They suggested these are signs the worms rebuilt their burrows using mucus to strengthen their walls, since bacteria that feed on such mucus are known to produce iron-rich environments.

Trace fossils can help shed light on creatures with soft bodies that rarely fossilize well. These newfound fossils are among the first to hint that invertebrates fed on vertebrates, Löwemark noted. "Usually vertebrates such as fish feed on invertebrates such as worms," he said. "Here, the table has been turned!"

Löwemark and his colleagues detailed their findings online Jan. 21 in the journal Scientific Reports.

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Author Bio & Story Archive

Charles Q. Choi is a science reporter who has written for Scientific American, The New York Times, Wired, Science, Nature, and National Geographic News, among others.