Ancient ocean mystery deepens as long-misidentified fossil is finally revealed by researchers

More than 2 decades aft scientists identified a fossil arsenic the world's oldest octopus — officials present accidental it wasn't 1 astatine all.

A caller survey published successful the diary Proceedings of the Royal Society B recovered that the fossil Pohlsepia mazonensis — a 300-million-year-old oversea carnal recovered successful the Mazon Creek fossil beds of northeastern Illinois — was person to a nautilus than an octopus.

Researchers present judge the carnal was a comparative of the nautilus, which is simply a shell-covered cephalopod with tentacles.

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Cephalopods are a people of marine animals that includes octopuses, squids and cuttlefish, and are known for their tentacles and precocious tense systems — and for lacking rigid skeletons.

The fossil was identified arsenic the world's oldest octopus successful 2000 — but is present considered the oldest soft-tissue nautilus successful the world.

Researchers accidental the fossil's features, including its teeth, align much intimately with a nautilus comparative than an octopus. A representation of a nautilus is seen above. (iStock)

University of Reading zoologist Thomas Clements, the pb researcher of the caller study, told The Associated Press the fossil is simply a "very hard [one] to interpret."

He added, "To look astatine it, it benignant of conscionable looks similar a achromatic mush."

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"If you look astatine it, and you are a cephalopod researcher, and you’re funny successful everything octopus, it does superficially look a batch similar a deep-water octopus."

The determining factor, Clements said, was its teeth — which researchers examined utilizing a synchrotron to adjacent wrong the fossil.

The fossil was discovered successful the Mazon Creek fossil beds of northeastern Illinois. Seen above, the tract is known for preserving past marine life. (Audrey Richardson/Chicago Tribune/Tribune News Service via Getty Images)

They recovered that each enactment had 11 teeth — much than the 7 oregon 9 typically recovered successful octopuses.

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"This has excessively galore teeth, truthful it can’t beryllium an octopus," Clements said.

"And that’s however we realized that the world’s oldest octopus is really a fossil nautilus, not an octopus."

Researchers recovered the fossil had 11 teeth per row, much than typically seen successful octopuses — prompting a reclassification. (iStock)

The fossil had the aforesaid teeth arsenic a nautiloid called Paleocadmus pohli, an past carnal recovered successful the aforesaid area.

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Researchers accidental the mix-up apt occurred due to the fact that the carnal decomposed and mislaid its ammunition earlier it was fossilized.

"People person been questioning whether it was an octopus ever since the archetypal insubstantial was archetypal published successful 2000."

The adjacent oldest-known octopus fossil is astir 90 cardinal years aged — astir 210 cardinal years younger than the fossil Pohlsepia mazonensis.

"It’s a immense gap," Clements said, noting it had agelong raised questions.

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"And truthful that large spread got researchers benignant of questioning, ‘Is this happening really an octopus?'"

The fossil is presently held successful the Field Museum successful Chicago. 

Paul Mayer, who manages the museum's fossil invertebrate collections, said helium was "a small surprised" by the caller classification, but acknowledged that scientists person questioned the uncovering for years.

The Field Museum successful Chicago houses the fossil that has present been reclassified aft years of technological debate. (AP Photo/Kamil Krzaczynski, File)

"People person been questioning whether it was an octopus ever since the archetypal insubstantial was archetypal published successful 2000," Mayer told the AP.

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He added that the quality "is large for our collections, and hopefully caller discoveries volition beryllium made and caller stories volition beryllium revealed."

The Associated Press contributed reporting.