The ancient squid fossil turned out to be something else

For decades, scientists believe that a group of extinct marine animals called wild fruits are primitive squids.

But a new study of the fossil of Sirius Passat in North Greenland is bringing the story to the surface. These 500 million-year-old creatures are not distant cephalopod cousins, but are considered early relatives of arrow worms—simple, dart-shaped predators that still roam the oceans today. These ancient forms are more complex and dangerous than their modern counterparts.

Not a squid, not a cephalopod, but an older thing

The first is the wildlife described from the Burgess Shale in Canada and Chengjiang Biota in China, which some paleontologists have believed over the years represent the earliest known cephalopods. Their streamlined bodies, the eyes and side fins of large cameras have surface similarities to modern squids and cuttlefish. But, as Dr. Jakob Vinther of the University of Bristol said, “The assumption will subvert our original knowledge of cephalopods.”

New analysis was published on July 23 Science Advances25 beautifully preserved wild lettuce fossils were discovered from Sirius Passet’s nine years of on-site work. Thanks to the website’s rare preservation of soft tissue, including the nervous system, researchers were able to observe this set of features that had never been seen before.

The nervous clues change everything

Breakthrough, researchers noticed paired, arc-shaped structures in the middle of wild animals—peritoneal ganglion—a large number of neurons found only in arrow worms or chaetognaths.

“We found that our wild lettuce preserved part of its nervous system as a paired mineralized structure, a giveaway from these animals sitting in the tree of life,” Vinther said.

“These fossils retain a unique feature against arrow worms, called abdominal ganglia,” added Dr. Tae-Yoon Park of the Korean Polar Research Institute. In modern arrow worms, this abdomen brain is responsible for coordinating rapid swimming and predatory strikes.

What makes this discovery so surprising?

Today’s arrow worms are small and almost blind plankton hunters. But it turns out that their ancient ancestors were mature predators. New name Nektognathus evasmithae With sophisticated camera-shaped eyes, long-lasting sensory antennas, powerful muscles and a tooth-shaped inner jaw bone, it may allow it to swallow entire prey.

• Fossils show intestinal content including swimming arthropods ISOXYSindicating a meat-eating diet
• The jaw structure implies suction eating, not chewing
• Fin rays and muscle patterns reveal strong, agile swimmers
• The morphology of the nervous system is consistent with the stem population chaetagnaths

The species’ name honors Professor Eva Smith, a Danish human rights advocate who describes it as a “clever and sneaky warrior” just like the animals themselves.

Rewrite the early history of the predators

The study not only corrected the identity of the major Cambrian fossil groups, but also corrected the ecological role of early arrow worms. Before the rise of arthropods, their ancestors were no longer low-level plankton feeders, but instead occupied the top predatory niche.

“The ancestors of arrow worms were indeed complex predators, just like the squid that evolved about 400 million years later,” Vinther noted.

This reminds people that evolution not only establishes complexity, but also may lose it. Today’s arrow worms are shadows of their ancestors, just as birds evolved from Tyrannosaurus Rex but now dominate the sky in different ways.

From strange miracles to family history

Just as many Cambrian organisms were once considered to be mis-evolved, wild roots are no longer “strange miracles” but are familiar members of the genealogical lineage. “Stem groups like this help us not only understand how modern animals develop, but also understand what is wasted along the way,” Vinther said.

exist nektognathusmissing things include vision, body size, and even fatal grip.

Journal Information

Posted in Science Advances July 23, 2025
doi:10.1126/sciadv.adu6990

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