Portuguese 
English 
Spanish 
3 min of reading 
0 comments 
The fossil that was considered the oldest octopus in the world for over 20 years has just been reclassified as an extinct nautilus after analysis with the most powerful X-rays on the planet revealed hidden teeth in the rock
For more than two decades, a 300-million-year-old fossil found near Chicago was considered the oldest octopus ever discovered. Now, that classification has been overturned.
A study published on April 8, 2026, in the journal Proceedings of the Royal Society B revealed that the animal was not an octopus. In fact, it is a decomposed nautiloid, an extinct relative of modern nautiluses.
The discovery was made possible thanks to micro-CT scan technology with X-rays. Researchers used what they describe as “the most powerful X-rays in the world” to see inside the rock.
-
Mangroves hide a billion-dollar water cleanup, remove 960 thousand tons of nitrogen per year, and reveal an environmental power that many people hadn’t even imagined existed.
-
Researchers found evidence that the human brain can react to the Earth’s magnetic field, according to a study published in the journal eNeuro. The participants remained in a sealed chamber and didn’t even notice when the magnetic field was altered.
-
Sweden resumes in Luleå the largest dredging of its modern era and will remove 22 million cubic meters to take the port beyond its 50,000-ton limit, make way for 160,000-ton ships, and unlock the ore route in the Baltic Sea.
-
Brazil is in the race for the artificial sun with tokamaks, public research, and a global billion-dollar competition that aims to transform plasma at 100 million degrees into clean, safe, and almost inexhaustible energy for the planet’s future.
Thomas Clements, a professor of invertebrate zoology at the University of Reading in England, led the study. He explained what was found hidden in the fossil.
Tiny teeth hidden in the rock for 300 million years overturned a 20-year classification
“Basically, we used a wide range of new analytical techniques to uncover hidden anatomical features within the rock,” Clements stated.
The technique revealed a radula — a feeding structure — with at least 11 teeth per row. Modern octopuses have only 7 or 9 teeth per row.
“It was these tiny teeth that we found that allowed us to identify that it was not an octopus”, the researcher told CNN International on April 9.
“And we were able to determine that it is not an octopus, but actually a very decomposed nautiloid, which is a relative of modern nautiluses,” Clements added.
The fossil is called Pohlsepia mazonensis. It was found in Mazon Creek, Illinois, a geological formation known for its exceptional fossil preservation.
A 210-million-year gap in the history of octopuses
The reclassification has important implications for science. The Pohlsepia was the supposed oldest octopus by a huge margin: the next fossil octopus record is only 90 million years old.
This means that there was a 210-million-year gap between the Pohlsepia and the second oldest octopus. This gap has always intrigued paleontologists.
Now, the gap makes sense. The animal was never an octopus — it was a nautiloid with tentacles and an external shell that decomposed misleadingly.
“The research demonstrates the power of new technologies to advance our scientific understanding,” Clements concluded.
Mazon Creek: the paleontological site in Illinois that still holds surprises
Mazon Creek is an iconic paleontological site in the United States. Fossils preserved in concretions hold extraordinary details of organisms from the Carboniferous period.
As reported by R7, the previous classification as an octopus was based on superficial visual evidence. The new non-invasive imaging techniques have changed the game.
The reclassification does not invalidate all previous science. However, it corrects an interpretation that has been held for over 20 years. The case shows that ancient fossils can still surprise when reexamined with modern technology.
Be the first to react!