328-million-year-old fossil reveals octopus ancestors had ten arms

Octopuses have eight arms, but a new study published in Nature Communications suggests that the cephalopod’s earliest ancestors had two additional appendages.

Based on a 328-million-year-old fossil with ten sucker-laden arms, the study identifies a completely new species, vampyropod—the group that includes octopuses and vampire squid. It is the oldest known vampyropod that has increased the group’s fossil record by approximately 82 million years. 

Vampyropods have soft bodies, so they do not typically make good fossils. However, the latest research is based on an unusually well-preserved vampire-squid-like fossil from the Royal Ontario Museum’s holdings (ROM).

It is also the first and only vampyropod known to have ten functioning appendages, two of which appear elongated than the rest.

The number of arms distinguishes the 10-armed squid and cuttlefish line (Decabrachia) from the eight-armed octopus and vampire squid line (Vampyropoda). It’s been long understood that octopuses achieved the eight-arm count by eliminating the two filaments of the vampire squid and that these filaments are vestigial arms. However, all previously recorded fossil vampyropods with preserved appendages had just eight arms. Hence this specimen is perhaps the first proof of the theory that all cephalopods had ten arms in the past.

The fossil is named Syllipsimopodi bideni to honour the 46th President of the United States, Joseph R. Biden. The genus name is derived from the Greek word “syllípsimos,” meaning “prehensile” (capable of grasping), and “pódi,” meaning “foot.” It is the oldest known cephalopod to develop suckers, which allow the arms (modification of the molluscan foot) to grasp prey and other objects better.

Image Source: An artistic reconstruction of the newly described 328-million-year-old vampyropod. [© Katie Whalen]