A Misunderstanding Not of 5 Million, but 500 Million Years - The True Identity of Ancient Creatures Revealed! Not "Squid," but a Startling New Fact

"The fossil once thought to be an ancient 'squid' turned out to be an entirely different creature."

The mysterious creature Nectocaridid, excavated from the Sirius Passet in the Precambrian layers of northern Greenland, has been revealed by recent research to be a distant ancestor of arrow worms (Chaetognatha), named Nektognathus evasmihtae . Previously considered the "oldest cephalopod (relatives of squid and octopus)" and featured in textbooks, this "prototype of squid" swam as a different lineage of predator in the seas over 500 million years ago, not just 5 million years ago—a paradigm shift is occurring.

■ Collapse of the "Ancestor of Squid" Myth

In 2009, Nectocaridid discovered from the Burgess Shale in Canada, with fin-like fins, compound eyes, and tentacles resembling squid, was reported as a "great discovery tracing the origin of cephalopods back 500 million years." However, the team from the University of Bristol, Korean Polar Research Institute, and Copenhagen University reanalyzed 25 new specimens using X-ray and elemental mapping, confirming the preservation of a **large ventral ganglion specific to arrow worms** on the ventral side. Additionally, the morphology of the mouthparts and jaw apparatus matched the characteristics of the arrow worm lineage, completely refuting the cephalopod hypothesis.

■ "Super" Arrow Worm with Camera Eyes

Modern arrow worms are transparent, a few centimeters long, plankton predators, but Nektognathus was 10–15 cm long, equipped with complex camera eyes and swimming fins, and evidence of being a top predator was found, such as the shell of the arthropod Isoxys discovered in its digestive tract. This is an evolutionary reversal where "the ancestor of simple worms was actually a high-performance hunter."

■ SNS Buzzed with "#paleostream"

• "Drawing it and feeling it's 'not a squid' is interesting!" (@Shamu_blackfish)

• "Latest four species flocking: Palaeocampa, Nektognathus, and two others!" (@Katborg82)

• "I doodled the new star of the Cambrian 🎨" (@Aberrantologist)
  On X (formerly Twitter), the "#paleostream" community, which draws fossils live every week, reacted immediately. From amateurs to paleontologists, illustrations and memes were posted, and voices celebrating the conclusion of the 15-year debate of "squid faction vs. worm faction" followed one after another. X (formerly Twitter) X (formerly Twitter) X (formerly Twitter)

■ Researcher Comments

• Dr. Jakob Vinther "I had a sense of discomfort with the 'cephalopod hypothesis' 15 years ago. Finally, the puzzle is complete."

• Dr. Tae-Yoon Park "Even if the shapes are similar, the lineages are different. A good example of convergent evolution." Both stated that "the fact that the ancestor of arrow worms was a complex predator reshapes the image of apex predators in the Cambrian ecosystem."
  

■ Impact on Evolutionary History

1. Timeline of Cephalopod Origins Recalibrated

   • The appearance of the oldest cephalopods returns to about 400 million years ago.

2. Teaching Material for Convergent Evolution

   • Like mammals resembling fish (whales), a swimming lifestyle made them similar in form.

3. Update of Food Web Models

   • Possibility of diversification in the mid-level predator layer of the Cambrian sea.

■ Next Questions

• Why did arrow worms "devolve" their complex eyes?

• What fossils fill the time gap (about 400 million years) from Nektognathus to modern arrow worms?

• What is the genetic basis for the converged fin structure?

■ Conclusion

The impact of Nektognathus goes beyond merely rewriting classifications. It overturns the image of arrow worms as "transparent, small worms" and reveals the fierce hunter that existed in the Cambrian sea. Paleontology changes our view of the "present" every time the "past" changes. The day when the next fossil shakes our common sense is near.

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