Predatory worms known as "terror beasts" roamed the seas 500 million years ago

Scientists have unearthed fossils of a new group of ancient predatory worms in North Greenland’s Early Cambrian Sirius Passet fossil locality. The fossils, which are more than half a billion years old, represent a previously unknown dynasty of ocean predators.

The newly identified creatures, named Timorebestia, meaning “terror beasts” in Latin, challenge existing perceptions of early ocean ecosystems. 

Giant predatory worms

Unlike anything previously known, these giant predatory worms measured over 30 centimeters in length and had fins along their bodies.

They also boasted a distinct head with lengthy antennae, and substantial jaw structures. These features mark them as some of the largest swimming animals of the Early Cambrian period.

Dr. Jakob Vinther, a senior author of the study from the University of Bristol, highlighted the significance of this discovery. 

“We have previously known that early arthropods were the dominant predators during the Cambrian, such as the bizarre-looking anomalocaridids,” said Dr. Vinther.

“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.”

“Our research shows that these ancient ocean ecosystems were fairly complex with a food chain that allowed for several tiers of predators.”

“Timorebestia were giants of their day and would have been close to the top of the food chain. That makes it equivalent in importance to some of the top carnivores in modern oceans, such as sharks and seals back in the Cambrian period.”

Top marine predators 

Inside the fossilized digestive system of Timorebestia, researchers found remains of Isoxys, a common swimming arthropod. 

We can see these arthropods were a food source for many other animals, said study co-author Morten Lunde Nielsen.

“They are very common at Sirius Passet and had long protective spines, pointing both forwards and backwards. However, they clearly didn’t completely succeed in avoiding that fate, because Timorebestia munched on them in great quantities.”

The significance of Timorebestia extends beyond their predatory nature. Arrow worms, relatives of Timorebestia, are among the oldest animal fossils from the Cambrian period. 

While arthropods appear in the fossil record approximately 521 to 529 million years ago, arrow worms date back at least 538 million years. 

“Both arrow worms, and the more early Timorebestia, were swimming predators. 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 10-15 million years before they got superseded by other, and more successful, groups,” explained Dr. Vinther.

According to study co-author Luke Parry from Oxford University, Timorebestia is a really significant find for understanding where these jawed predators came from. 

Jaws inside its head

“Today, arrow worms have menacing bristles on the outside of their heads for catching prey, whereas Timorebestia has jaws inside its head,” said Parry.

“This is what we see in microscopic jaw worms today – organisms that arrow worms shared an ancestor with over half a billion years ago. Timorebestia and other fossils like it provide links between closely related organisms that today look very different.”

“Our discovery firms up how arrow worms evolved,” said study co-senior author Dr. Tae Yoon Park from the Korean Polar Research Institute, who was the expedition leader.

“Living arrow worms have a distinct nervous centre on their belly, called a ventral ganglion. It is entirely unique to these animals.”

“We have found this preserved in Timorebestia and another fossil called Amiskwia. People have debated whether or not Amiskwia was closely related to arrow worms, as part of their evolutionary stem lineage. The preservation of these unique ventral ganglia gives us a great deal more confidence in this hypothesis.”

Exciting findings about predatory worms

“We are very excited to have discovered such unique predators in Sirius Passet. Over a series of expeditions to the very remote Sirius Passet in the furthest reaches of North Greenland more than 82,5˚ north, we have collected a great diversity of exciting new organisms,” said Dr. Park.

“Thanks to the remarkable, exceptional preservation in Sirius Passet we can also reveal exciting anatomical details including their digestive system, muscle anatomy, and nervous systems.”

“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,” Dr. Park concluded.

Image Credit: Artwork by Bob Nicholls/@BobNichollsArt

The study is published in the journal Science Advances. 

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