For the roughly 300 known species of octopus that inhabit the world’s oceans, having eight arms is a defining characteristic. But that’s not how it started.
Scientists said Tuesday that a fossil unearthed in central Montana of a species called Syllipsimopodi bideni represents the oldest known relative of today’s octopuses and has ten arms, two of which are twice as long as the other eight.
The fossil, so well preserved that it reveals two parallel rows of suckers on each arm, dates to about 328 million years.
O Syllipsimopodi, about 12 centimeters long, had a torpedo-shaped body and the appearance of a squid, although it was not closely related to the squid, which appeared much later. It is also the oldest known creature with suction cups, which allow its arms to better grip prey and other objects.
“The fossil greatly changes our understanding of how octopuses evolved, and indicates that the first members of the group superficially resembled squid,” said paleontologist Christopher Whalen, a postdoctoral fellow at the American Museum of Natural History in New York and Yale University. and lead author of the study, published in the journal Nature Communications.
The soft bodies of octopuses typically do not lend themselves to fossilization, complicating the study of the animal’s evolution.
Octopuses, which range from the 1-inch star-sucking pygmy octopus to the 30-foot giant Pacific octopus, are known for their otherworldly appearance, with bulbous heads, large eyes, and beak-shaped jaws.
They are adept at camouflage — they change colors and even textures to mimic their surroundings — and can maneuver their bodies into small cracks and crevices. They are also able to use tools and solve problems.
“Octopuses are the smartest invertebrates, and they’re among the smartest animals overall. It’s fascinating to see where these unique animals evolved from,” Whalen said.
O Syllipsimopodi It lies 82 million years before the origin of a group called vampires, which includes modern-day octopuses and the world’s only vampire squid species, a misnomer because it’s not a squid but a cousin of the octopus.
The very word “octopus” in English, “octopus”, means eight feet. O Syllipsimopodi represents the only member of the octopus lineage with ten arms, meaning that two were lost in later evolution.
There are numerous similar examples in the history of life on Earth, such as the reduction in the number of toes seen in carnivorous dinosaurs or horses.
Today’s vampire squid have eight arms and two thin filaments that scientists have long considered vestiges of ancient arms. Octopuses do not have these vestigial filaments.
“O Syllipsimopodi is the first fossil to demonstrate that, yes, vampiropods had ten arms ancestors, as had been predicted,” Whalen said.
Two of the arms of Syllipsimopodi were about 3.8 cm long, and the other eight were half that size, in a squid-like configuration.
“Capturing prey is facilitated by the two longer tentacles, with the eight shorter arms helping to manipulate the prey and bring it to the beak,” said study co-author Neil Landman, an invertebrate paleontologist at the American Museum of Natural History. .
O Syllipsimopodi lived in the warm waters of a tropical bay—Montana at the time was situated close to the equator. It may have been a mid-level predator, eating smaller invertebrates.
Octopuses are cephalopods, a group of marine invertebrates dating back about 530 million years and distinguished by having arms or tentacles. Cephalopods today include squid, cuttlefish, and nautilus.
O Syllipsimopodi lived in the Carboniferous period, a time of important evolutionary changes in other forms of marine life that included the appearance of more modern-looking fish.
Syllipsimopodi means “prehensile foot”—their arms are an evolutionary modification of the clam foot—and bideni honors US President Joe Biden, who had just been sworn in when the study was submitted for publication.
Translated by Luiz Roberto M. Gonçalves
