Scientists have discovered the oldest known ancestor of octopuses - a fossil about 330 million years old, found in the US state of Montana, the Associated Press reported.

Researchers have concluded that the ancient creature lived millions of years earlier than previously thought, meaning that octopuses originated before the dinosaur era.

The find, which measures 12 centimeters, has ten tentacles - modern octopuses have eight - each with two rows of suction organs.

The ancient creature probably inhabited a shallow, tropical ocean bay.

"Soft tissue fossils are very rare, except in a few places," said Mike Vecchione, a zoologist at the Smithsonian's National Museum of Natural History.

He did not participate in the study.

"It's a very exciting discovery."

The find was excavated at the Bear Gulch limestone formation in Montana and donated to the Royal Ontario Museum in Canada in 1988.

For decades, fossils have been neglected in a drawer as scientists analyze fossil sharks and other finds from the same site.

However, paleontologists have noticed ten small tentacles wrapped in limestone.

The well-preserved fossil also provides "some evidence of an ink bag" probably used against predators, just like modern octopuses, said Christopher Whelan, a paleontologist at the American Museum of Natural History and co-author of the study, published in the Nature Communications Journal.

The creature, the so-called

vampire, probably the ancestor of both modern octopuses and squid vampires - sea creatures with confusing names who are much closer to an octopus than to a squid.

Previously, the "oldest known" vampire date back about 240 million years, according to the study's authors.

Scientists have named the fossils Syllipsimopodi bideni after US President Joe Biden.

They did so in admiration of the scientific and research priorities of the head of state, adds BTA.