Scientists have uncovered fossils of a new group of predatory animals from the Early Cambrian Sirius Passet locality in northern Greenland. Dating back over 518 million years, these large worms were potentially some of the first animal carnivores to inhabit the water column, revealing a dynasty of hunters previously unknown to science.

The new fossil creatures have been named Timorebestia, meaning “terror beasts” in Latin. Adorned with fins along the sides of their bodies, distinctive head regions with long antennas, enormous jaw structures inside their mouths, and lengths over 30 cm, they were among the largest swimming animals of the early Cambrium period.

Until now, we knew that primitive arthropods like the bizarre-looking anomalocaridids dominated as predators during the Cambrian, explains Jakob Vinther of the Universities of Bristol’s School of Earth Sciences and School of Biological Sciences, and lead author of the study.

However, Timorebestia is a distant but close relative of modern arrow worms or chaetognaths – much smaller oceanic predators that feed on tiny zooplankton.

Our research demonstrates that these ancient ocean ecosystems were quite complex, with a food chain that allowed for multiple levels of predators, Vinther said. As giants of their time, Timorebestia would have been near the top of the food chain, equivalent in importance to modern apex predators like sharks and seals.

Inside the fossilized digestive tracts of Timorebestia, researchers found remains of a common swimming arthropod called Isoxys. We can see these arthropods were a food source for many other animals, said co-author Morten Lunde Nielsen. They were very abundant in Sirius Passet and had long spiny defenses pointing both forwards and backwards, but clearly Timorebestia consumed them in large numbers.

Arrow worms are among the oldest known animal fossils from the Cambrian period, dating back at least 538 million years. Dr. Vinther explained, Both arrow worms and the more primitive Timorebestia were swimming predators, so we can assume they likely dominated oceans before the rise of arthropods, perhaps enjoying a 10-15 million year dynasty.

Co-author Luke Parry of the University of Oxford added, Timorebestia is a really significant find for understanding where these jaw-bearing predators came from. While living arrow worms use barbed bristles to capture prey, Timorebestia had internal jaws – a trait now seen in microscopic micrognathozoan worms that shared a common ancestor with arrow worms over 500 million years ago. Fossils like Timorebestia provide links between once very different-looking but closely-related organisms.

Lead author Tae Yoon Park of the Korean Polar Research Institute concluded, Through a series of expeditions to the remote Sirius Passet locality in the high Arctic of Greenland, we’ve uncovered a great diversity of new and fascinating organisms. Thanks to Sirius Passet’s extraordinary fossil preservation, we can also reveal interesting anatomical details like its digestive system, muscle structure and nervous system. We have many more interesting finds to share that will help show what these early animal ecosystems were like and how they evolved.


University of Bristol | Tae-Yoon S. Park et al. ,A giant stem-group chaetognath. Sci. Adv.10,eadi6678(2024). DOI:10.1126/sciadv.adi6678

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