Scientists Discover Fossils Of ‘Terror Beast’ Worms That Ruled The Oceans 518 Million Years Ago

Published January 18, 2024
Updated January 19, 2024

Timorebestia was an ancient relative of the modern arrow worm — and one of the deadliest predators of its time.

Timorebestia Fossils

Bob Nicholls/University of BristolAn artist’s depiction of the ancient “terror beast” worms.

Researchers in northern Greenland recently uncovered fossils of giant predator worms that ruled the oceans 518 million years ago — and they dubbed them “terror beasts.”

These massive worms, named Timorebestia — meaning “terror beasts” in Latin — were some of Earth’s earliest carnivorous aquatic animals, according to a release from the research team at the University of Bristol.

The ancient predators had bodies lined with fins, long antennae protruding from their heads, and massive jaw structures. Reaching nearly a foot in length, they were among the largest ocean creatures during the Early Cambrian period.

“We have previously known that primitive arthropods were the dominant predators during the Cambrian,” said Dr. Jakob Vinther, a senior author on the study, which was published in Science Advances. “However, Timorebestia is a distant, but close, relative of living arrow worms, or chaetognaths. These are much smaller ocean predators today that feed on tiny zooplankton.”

As Vinther explained, research into these ancient ecosystems has shown that they were “fairly complex” and had a “food chain that allowed for several tiers of predators.”

Jakob Vinther

Dr. Jakob Vinther/University of BristolDr. Jakob Vinther with a Timorebestia fossil.

Although the idea of “terror” worms might bring to mind something from Frank Herbert’s Dune or the Alaskan Bull Worm from SpongeBob SquarePants, don’t let the foot-long length of these ancient predators fool you — these worms were “giants of their day,” as Vinther noted.

“[Timorebestia] would have been close to the top of the food chain. That makes it equivalent to some of the top carnivores in modern oceans, such as sharks and seals,” said Vinther.

Though the modern descendants of Timorebestia, arrow worms, are much smaller than their terrifying ancestors, scientists found surprising similarities between the two species given that they lived 500 million years apart.

“Both arrow worms, and the more primitive Timorebestia, were swimming predators,” Vinther explained. “We can therefore surmise that in all likelihood they were the predators that dominated the oceans before arthropods took off. Perhaps they had a dynasty of about 10 [to] 15 million years before they got superseded by other, and more successful, groups.”

Likewise, Tae Yoon Park of the Korean Polar Research Institute, another senior author on the study, noted that both arrow worms and the primitive Timorebestia had a similar, distinct nervous center on their stomach known as a ventral ganglion.

“It is entirely unique to these animals,” Park stated. “We have found this preserved in Timorebestia.”

“Our discovery firms up how arrow worms evolved,” said Park.

Timorebestia Fossil

Dr. Jakob Vinther/University of BristolA Timorebestia fossil.

Park also noted how extraordinarily well-preserved the fossils were after half a billion years: “Thanks to the remarkable, exceptional preservation… we can also reveal exciting anatomical details including their digestive system, muscle anatomy, and nervous systems.”

Within the fossilized digestive system of Timorebestia, researchers found remains of an arthropod known as Isoxys. Another scientist involved with the study, Morten Lunde Nielsen, explained, “Timorebestia munched on them in great quantities.”

Researchers said that future fossil discoveries could help to further unravel the mysteries of Earth’s earliest animal ecosystems and their evolution over the course of millennia.

“We are very excited to have discovered such unique predators,” Park said. “Over a series of expeditions to the very remote Sirius Passet in the furthest reaches of North Greenland… we have collected a great diversity of exciting new organisms.”

“We have many more exciting findings to share in the coming years that will help show how the earliest animal ecosystems looked like and evolved,” Park added.


After learning about these terrifying ancient predators, read about this 558-million-year-old fossil that might just be the world’s oldest animal. Or, learn all about this ancient shark relative that looked like an eel.

Austin Harvey
A staff writer for All That's Interesting, Austin Harvey has also had work published with Discover Magazine, Giddy, and Lucid covering topics on mental health, sexual health, history, and sociology. He holds a Bachelor's degree from Point Park University.
John Kuroski
John Kuroski is the editorial director of All That's Interesting. He graduated from New York University with a degree in history, earning a place in the Phi Alpha Theta honor society for history students. An editor at All That's Interesting since 2015, his areas of interest include modern history and true crime.