Octopus ancestor with 10 arms named after President Joe Biden

Following a train station, an ice cream flavour and a planet, Joe Biden can now add a fossil octopus to the list of things named after him.

Dating to over 328 million years ago, Syllipsimopodi bideni pushes back the fossil record of the vampyropods, the group of cephalopods containing octopus and vampire squid, by over 82 million years. It suggests that the first cephalopods all had 10 arms, two of which have been lost in the intervening period during the evolution of modern octopuses.

Dr Christopher Whalen, the lead author of the description of the fossil species, says, 'This is the first and only known vampyropod to possess 10 functional appendages.

'The arm count is one of the defining characteristics separating the Decabrachia, which include 10-armed squid and cuttlefish, from the Vampyropoda, which are made up of eight-armed octopus and vampire squid. 

'We have long understood that octopuses achieved their eight-arm count through elimination of the two filaments of vampire squid, and that these filaments are vestigial arms.  

'However, all previously reported fossil vampyropods preserving the appendages only have eight arms, so this fossil is arguably the first confirmation of the idea that all cephalopods ancestrally possessed ten arms.'

Zoë Hughes, the Museum's Curator of fossil invertebrates and who was not involved with the description, says, 'Vampyropods as a group have eight arms generally, so a species with 10 is quite interesting.

'Furthermore, the quality of the taxonomy of the coleoids depends on the fossils that are found, as we generally base it on rare fossils.

'The completeness of this specimen gives us some evolutionary ideas as we don't know a lot about a lot of these groups. This will help to fill in some of the knowledge gaps that we've previously had to make inferences about.'

The fossil species' description is published in Nature Communications.  

The evolution of the vampyropods

The vampyropods are a main group of cephalopods, a class which include extinct animals like ammonites and belemnites as well as living animals such as nautiluses and cuttlefish. While their hard tissues preserves easily, it's not the same case with their softer parts.

'The cephalopods as a whole fossilise well, but it depends on which group is being looked at,' says Zoë. 'There are three subclasses, which are the Ammonoidea, the Nautiloidea and the Coleoidea.

'All cephalopods had a chambered shell known as the phragmacone at some point in their evolution, which is external in the Ammonoidea and Nautiloidea.

'In the coleoids, however, they had an internal one which has been lost for the most part through their evolution. As a result, these animals are mostly soft tissue so they aren't preserved as well.

'Most of the fossil coleoids in the Museum's collections are belemnites, which have a mineralised, bullet-shaped internal structure called a guard that preserves more easily.  It is these remains which we find most often, and we rarely see the phragmacone or soft tissues.

'Quite specific circumstances are needed for the soft tissue to become preserved, which is why these fossils are quite rare.'

So while genetic evidence suggested that the coleoids could date back over 300 million years, the earliest fossil only dates to around 240 million years ago. 

These genetic estimates have now been validated with S. bideni, which was found in rocks in Montana dated to between 330 and 323 million years ago. It was donated to the Royal Ontario Museum in the 1980s and recently recognised as its own species and genus by researchers working there.

The fossil is streamlined, with a 12-centimetre-long body similar to those of modern squids. However, while squid have eight arms and two tentacles, all of S. bideni's limbs are arms, as they have suckers along their entire length.

These arms would likely have been used to capture and manipulate prey, while using the fins on its body to stabilise itself while swimming.

Co-author Dr Neil Landman says, 'S. bideni may have filled a niche more similar to extant squids as a midlevel aquatic predator.  

'It is not inconceivable that it might have used its sucker-laden arms to pry small ammonoids out of their shells or ventured more inshore to prey on brachiopods, bivalves, or other shelled marine animals.'

Beyond offering a glimpse of how early vampyropods could have looked, the new species also offers a chance to work out how the cephalopods developed over time.  

Presidential honours

By examining S. bideni, the scientists suggest that the early members of the group lost the chambered section of their shell over time, with an internal structure known as a pen the last remaining fragment of the shell.

This would have allowed them to manipulate their buoyancy more easily, using water and compounds such as ammonia to make themselves less dense than the surrounding saltwater, rather than relying on gas pressure in the shell.

Subsequently, a pair of the arms were also lost as the body became more recognisably like modern octopuses. The scientists argue that their proposed method of evolution for the group is more plausible than existing explanations, requiring fewer genetic changes to achieve. 

The arms of Syllipsimopodi bideni are also responsible for its genus name, with the name translating as 'prehensile feet'. This is because cephalopod arms are somewhat confusingly derived from tissue that forms the foot in other molluscs.

Its species name, meanwhile, honours the current US President, Joe Biden. The vampyropod is the first species to be named after the 46th president, but many of his predecessors have also shared the honour of having an organism named after them. 

This includes insects named after George Washington, Abraham Lincoln and Ronald Reagan, fish named after Jimmy Carter and Bill Clinton as well as a flatworm named after Barack Obama. Neopalpa donaldtrumpi, meanwhile, is a moth named due to its head's resemblance to that of the 45th president.