Researchers at the American Museum of Natural History and Yale describe the oldest ancestor of octopuses and vampire squids. The 328-million-year-old fossil pushes the age of this group of animals back by some 82 million years, and held another surprise for scientists — it sported 10 arms, not 8.
The newly-described fossil species was christened Syllipsimopodi bideni. The name is rooted in the Greek word “syllípsimos” for “prehensile” and “pódi” for “foot”, with the second part honoring the 46th President of the United States, Joseph R. Biden. Taxonomically speaking, the species was a vampyropod, having the distinction of being the oldest common ancestors of cuttlefish, octopi, and vampire squids.
“This is the first and only known vampyropod to possess 10 functional appendages,” said lead author Christopher Whalen, a postdoctoral researcher in the Museum’s Division of Paleontology and a National Science Foundation postdoctoral fellow in Yale’s Department of Earth & Planetary Sciences.
“The arm count is one of the defining characteristics separating the 10-armed squid and cuttlefish line (Decabrachia) from the eight armed octopus and vampire squid line (Vampyropoda). We have long understood that octopuses achieve the eight arm count through elimination of the two filaments of vampire squid, and that these filaments are vestigial arms,” Whalen adds. “However, all previously reported fossil vampyropods preserving the appendages only have 8 arms, so this fossil is arguably the first confirmation of the idea that all cephalopods ancestrally possessed ten arms.”
Vampyropods today are soft-bodied cephalopods (a sub-type of mollusks) whose bodies grow around an internal chitinous shell. Fossils of vampyropods are very rare because their body structure does not lend well to fossilization. The current finding is an exceptionally well-preserved specimen that was originally discovered in what today is the state of Montana. After discovery, the fossil was eventually donated to the Royal Ontario Museum in 1988. Here it lay unexamined and undescribed until the present study.
Whalen and coauthor Neil Landman, curator emeritus in the Museum’s Division of Paleontology, identified the fossil as belonging to a completely new species and dated it at about 328 million years old. This marks the specimen as the single oldest vampyropod ever found by roughly 82 million years. The specimen’s arms all have well-preserved suckers, confirming hypotheses that the common ancestor of vampyropods, octopi, and cuttlefish had 10 arms, with some of these animals evolving to lose 2 retractable arms.
These two arms appear to have been much longer than the other eight. The animal had a bolt-like shape that’s very similar to that of modern squids.
“Syllipsimopodi may have filled a niche more similar to extant squids, a midlevel aquatic predator,” said Landman. “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.”
This fossil, the team explains, challenges our current understanding of the origin of vampyropods, suggesting that a new model of the evolution of these animals needs to be developed to fit with the findings.
The paper “Fossil coleoid cephalopod from the Mississippian Bear Gulch Lagerstätte sheds light on early vampyropod evolution” has been published in the journal Nature Communications.