(CNN)The oldest ancestor of modern octopuses lived 328 million years ago and had 10 arms, according to a new study. Researchers have named the previously unknown species Syllipsimopodi bideni after US President Joe Biden.
Fossil of 328 million-year-old octopus relative still has suckers on its arms
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The creature's discovery pushes back the time frame when vampyropods, the group to which cephalopods like octopuses belong, appeared in the ocean by almost 82 million years.
The study published Tuesday in the journal Nature Communications.
Vampyropods are known for having eight legs, an internal shell made of chitin and a soft body -- the last of which doesn't show up often in the fossil record because it tends to deteriorate more quickly than hard structures like bone.
A well-preserved fossil was discovered in Montana's Bear Gulch Limestone formation and donated to Canada's Royal Ontario Museum in 1988. The specimen represents the earliest-known ancient relative of these creatures, a new analysis of the fossil revealed.
"This is the first and only known vampyropod to possess 10 functional appendages," said study author Christopher Whalen, a postdoctoral researcher in the American Museum of Natural History's Division of Paleontology, in a statement.
"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."
Syllipsimopodi is the best known fossil for understanding how vampyropods originated, as well as helping researchers to trace their evolution, said Whalen, who is also a National Science Foundation postdoctoral fellow in Yale University's Department of Earth & Planetary Sciences.
It has long been thought by researchers that the vampyropods began with 10 arms and eventually lost two of them over time -- and now, scientists have direct evidence.
The detailed fossil clearly shows a creature about 4.7 inches (12 centimeters) long with 10 arms, with the suckers still attached -- an incredibly rare find since these arms were essentially just muscle. Two of those arms seem to be longer than the other eight, and its body was shaped like a torpedo, similar to modern squid. The researchers also found remnants of its ink sac.
Soft-bodied cephalopods are divided into vampyropods and decabrachians.
Vampyropods include octopuses and vampire squids, both of which are different from actual squid. Vampire squid basically look like octopuses with a built-in parachute because they have a membrane that stretches between and connects their arms. They also have two structures to help them feed called filaments in addition to their eight arms.
Meanwhile, decabrachians include modern squids and cuttlefish, which have 10 arms, including 2 tentacles. There are a number of differences that separate cephalopods like squid and octopuses, but the number of arms is one of the most recognizable.
So why is this fossil considered to be a vampyropod, even though it has 10 arms?
The team's phylogenetic analysis, which indicates evolutionary relationships, placed the species within the vampyropod side of the evolutionary tree, Whalen said.
The new species also had several key anatomical traits that mark it as a vampyropod, including the loss of a chambered cephalopod shell used to regulate buoyancy, called a phragmocone, which is seen in existing creatures like nautilus.
"The age makes the fossil very significant -- it indicates that vampyropods (and by extension decabrachians) are much older than was previously thought (at least 82 million years older)," Whalen said. "It indicates that there is a long interval of time during which fossil vampyropods must have existed but have not yet been found."
Syllipsimopodi likely used its longest pair of arms to capture prey and the rest of its shorter arms to hold small creatures and pry them from their shells. It also had fins, which probably helped it maintain stability and swim.
"Syllipsimopodi may have filled a niche more similar to extant squids, a midlevel aquatic predator," said study coauthor Neil Landman, a curator emeritus in the American Museum of Natural History's Division of Paleontology, in a statement.
The team was surprised to discover that Syllipsimopodi had a gladius, or the tongue-shaped and semitransparent part of a cephalopod's internal shell.
"The gladius functions to provide structural support, as a rigid structure that the muscles can pull against, and as an anchor for the fins (the overall function is similar to our bones)," Whalen wrote in an email.
"A gladius is considered a rather advanced feature in the grand scheme of cephalopod evolution. Today, only squids and their relatives, and vampire squid, have a gladius. Octopods have reduced it to a fin support or stylets, which are small, hard, bar-shaped structures."
The creature's genus name, Syllipsimopodi, is a nod to the Greek word "syllípsimos," meaning "prehensile," and "pódi" for foot because it's the oldest cephalpod discovered so far to have suckers on its arms. And the species name, bideni, is in honor of Biden, who had just been inaugurated when the study was first submitted for publication.
"I was encouraged by the plans President Biden put forward to counter anthropogenic climate change, and his general sentiment that politicians should listen to scientists," Whalen said.