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‘Octo’ means eight – but this ancient octopus had 10 arms

Reuters, March 15, 2022 6:30PM Kids News

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A 328-million-year-old octopus fossil suggests that this red octopus’ ancient ancestor actually had 10 arms instead of the eight that the entire species is named for. Picture: Schmidt Ocean Institute media_cameraA 328-million-year-old octopus fossil suggests that this red octopus’ ancient ancestor actually had 10 arms instead of the eight that the entire species is named for. Picture: Schmidt Ocean Institute


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For the roughly 300 known octopus species living in the world’s oceans, having eight arms is a defining* feature. But that is not how their story began.

American scientists announced on March 8 that a fossil* found in Montana represents the oldest-known relative of today’s octopuses and has 10 arms, with two twice as long as the other eight. The fossil, so well preserved that it reveals two parallel rows of suckers up and down each arm, dates to about 328 million years ago – nearly 80 million years before the age of dinosaurs.

The species, named Syllipsimopodi bideni, about 12 cm long, had a torpedo-shaped body and squid-like appearance – although it was not closely related to squids, which appeared much later. It is also the oldest known creature with suckers, which enabled the arms to better grasp prey and other objects.

media_cameraAn artistic reconstruction of the newly described 328-million-year-old vampyropod. Picture: American Museum of Natural History/Katie Whalen

“The fossil greatly changes our understanding of how octopuses evolved* and indicates that the earliest members of the group superficially* resembled living squids,” said American Museum of Natural History and Yale University postdoctoral* fellow, palaeontologist* Dr Christopher Whalen.

Soft octopus bodies generally do not fossilise well, making octopus evolution harder to study.

Smithsonian National Museum of Natural History zoologist* Dr Mike Vecchione, who was not involved in the study, told AP it was “very rare” to find soft tissue fossils.

“This is a very exciting finding,” he said. “It pushes back the ancestry* much farther than previously known.”

Octopuses – ranging from the 2.5cm star-sucker pygmy* octopus to the 9m giant Pacific octopus – are known for their otherworldly* appearance, with bulbous* heads, large eyes and beaklike jaws. They are adept at camouflage* – changing colours and even textures to mimic their surroundings – and can manoeuvre their bodies into tiny cracks and crevices. They are also capable of tool use and problem-solving.

media_cameraThe fossil was the first to show that vampyropods did ancestrally possess 10 arms and superficially resembled today’s squids. Picture: American Museum of Natural History/Katie Whalen

“Octopuses are the most intelligent invertebrates*, and among the most intelligent animals overall. It is fascinating to see what these unique animals started from,” Dr Whalen said.

Lead author of the study published in the journal Nature Communications, he said the fossil also “shows some evidence of an ink sac,” probably used to squirt out a dark liquid cloak to help to evade* predators, just like modern octopuses.

Syllipsimopodi pushes back by 82 million years the origins of a group called vampyropods* that includes today’s octopuses and the world’s lone species of vampire squid, which is not a squid at all but an octopus cousin.

The word “octopus” even translates as “eight feet” in Ancient Greek – Syllipsimopodi is the only known member of the octopus lineage* with 10 arms, meaning two were lost in later evolution.

ethereal octopus from the depth (Octopus vulgaris) media_cameraGifted in the art of camouflage, problem-solvers and handy with tools, octopuses are regarded as the most intelligent invertebrates and among the most intelligent animals overall. Picture: iStock

The fossil was the first to show that vampyropods did ancestrally possess 10 arms as previously predicted, Dr Whalen said.

Two of Syllipsimopodi’s arms were about 2.5-4cm long and the other eight half that length, a squid-like configuration.

“Capture of prey is facilitated by the two longer tentacles with the eight shorter arms helping to manipulate the prey and transport it to the beak,” said American Museum of Natural History invertebrate palaeontologist and study co-author Dr Neil Landman.

Syllipsimopodi prowled the warm waters of a tropical bay and may have eaten smaller invertebrates.

Octopuses are cephalopods, a marine invertebrate group dating back to roughly 530 million years ago and distinguished by having arms or tentacles. Cephalopods today also include squids, cuttlefishes and nautiluses.

Syllipsimopodi lived during the Carboniferous Period*, a time of important evolutionary changes in other marine life that included the appearance of more modern-looking fishes.

Including “bideni” in the fossil’s name recognises current US President Joe Biden, who had just been inaugurated* when the study was submitted for publication.

According to AP reports, the fossil spent decades after it was found sitting in a drawer at the Royal Ontario Museum in Canada until eagle-eyed palaeontologists noticed the 10 tiny limbs encased in limestone.

An exceptionally well-preserved vampyropod fossil from the collections of the Royal Ontario Museum (ROM) that the new study is based on. The fossil was originally discovered in what is now Montana and donated to ROM in 1988. Source: American Museum of Natural History/S Thurston media_cameraThe exceptionally well-preserved vampyropod fossil was discovered in Montana and donated to the Royal Ontario Museum in Canada in 1988. Picture: American Museum of Natural History/S Thurston

Additional reporting by AP


  • defining: fundamental, essential, inseparable, decisive
  • fossil: preserved remains, impressions or traces of an animal or plant from a past age
  • evolved: gradually changed or developed over time
  • superficially: taking in the outward or surface appearance only, not the whole picture
  • postdoctoral: research or post undertaken by a Doctor of Philosophy (PhD)
  • palaeontologist: specialist who studies fossils to learn the ancient history of life on Earth
  • zoologist: specialist in the scientific study of animals, from cells to evolution
  • ancestry: lineage, line of descent, origin of a family or species
  • pygmy: any example of a species that is very small
  • otherworldly: unusual, dreamy, mystical, mysterious
  • bulbous: bulging, round, big
  • camouflage: hide or disguise the presence of something or someone
  • invertebrates: any species of animal without a backbone
  • evade: avoid, dodge, escape
  • vampyropods: soft-bodied cephalopods that typically have eight arms
  • lineage: ancestry, direct descent from an ancestor
  • Carboniferous Period: named for large underground coal deposit that date to it
  • inaugurated: sworn in, initiated, instituted, formally admitted to office


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  1. How many known species of octopus live in the ocean?
  2. How old is the Montana fossil thought to be?
  3. What does “octopus” mean in Ancient Greek?
  4. How does Dr Landman suggest Syllipsimopodi captured prey?
  5. What does this fossil’s name have to do with US President Joe Biden?


1. Octopus dance
After reading all these facts and figures about octopuses, work with a friend to create an octopus dance. Use each other’s arms as tentacles and make a few more out of resources you can find in the classroom.

While you are performing your octopus dance, say some key facts about the creature to share your knowledge learned from the article.

Perform your dance to the class.

Time: allow 25 minutes to complete this activity
Curriculum Links: Science; Dance; Critical and Creative Thinking

2. Extension
Create a dateline from the date octopuses were first discovered to how they evolved over time to the species they are today.

Time: allow 20 minutes to complete this activity
Curriculum Links: Science

An adjective is a describing word. They are often found describing a noun. To start with, look at the words before the nouns.

Search for all the adjectives you can find in the article

Did you find any repeat adjectives or are they all different?

Pick three of your favourite adjectives from the text and put them in your own sentences to show other ways to use them.

Have you used any in your writing?

Extra Reading in animals