'Oldest octopus' turns out not to be an octopus at all - study

It's about revising evolutionary history.

Details

A Pohlsepia mazonensis fossil found in Illinois, USA, has been thought to be the oldest octopus since 2000.

To verify this, researchers used synchrotron scanning, a technique that allows them to study the structure within the rock.

The analysis showed:

• there was a radula inside, an organ with rows of small "teeth"
• with at least 11 elements in one row
• octopuses usually have 7 or 9, nautiloids have about 13

These features indicate that the animal was a relative of nautilus, not octopus.

In addition, the structure matched already known nautiloid fossils from the same region.

The fossil was initially mistaken for an octopus because of its appearance.

Scientists note:

• the body was partially decomposed before burial
• the soft tissues were deformed
• the structure became tentacle-like

This created a false impression that persisted for decades.

Why it matters

The results are changing ideas about cephalopod evolution.

Scientists say

• octopuses evolved later than thought
• the divergence from other cephalopods was not 300 million years ago
• finding provides rare data on soft tissues of ancient marine animals

Background

The fossil was previously thought to push back the appearance of octopuses by 150 million years ago.

That theory has now been disproved.

Source

The study is based on synchrotron scanning of the fossil from Illinois (USA). The work is published in rspb.royalsocietypublishing.org (2026).