Fossil coleoid cephalopod from the Mississippian Bear Gulch Lagerstatte sheds light on early vampyropod evolution

We describe an exceptionally well-preserved vampyropod, Syllipsimopodi bideni gen. et sp. nov., from the Carboniferous (Mississippian) Bear Gulch Lagerstatte of Montana, USA. The specimen possesses a gladius and ten robust arms bearing biserial rows of suckers; it is the only known vampyropod to retain the ancestral ten-arm condition. Syllipsimopodi is the oldest definitive vampyropod and crown coleoid, pushing back the fossil record of this group by similar to 81.9 million years, corroborating molecular clock estimates. Using a Bayesian tip-dated phylogeny of fossil neocoleoid cephalopods, we demonstrate that Syllipsimopodi is the earliest-diverging known vampyropod. This strongly challenges the common hypothesis that vampyropods descended from a Triassic phragmoteuthid belemnoid. As early as the Mississippian, vampyropods were evidently characterized by the loss of the chambered phragmocone and primordial rostrum-traits retained in belemnoids and many extant decabrachians. A pair of arms may have been elongated, which when combined with the long gladius and terminal fins, indicates that the morphology of the earliest vampyropods superficially resembled extant squids.

Automated summary

We have described a well-preserved ancient vampire squid, Syllipsimopodi bideni, from the Carboniferous period in Montana, USA. This specimen, with a gladius and ten arms with double rows of suckers, is the only known vampire squid with the ancestral ten-arm condition. Syllipsimopodi is the oldest confirmed vampire squid and crown coleoid, pushing back the fossil record of this group by approximately 81.9 million years, supporting molecular clock estimates. Our study using Bayesian analysis of fossil cephalopods shows that Syllipsimopodi is the earliest-diverging vampire squid known, challenging the common hypothesis that vampire squids descended from Triassic phragmoteuthid belemnoids. As early as the Mississippian period, vampire squids already exhibited the loss of the chambered phragmocone and primordial rostrum, traits retained in belemnoids and many extant decabrachians. The elongation of a pair of arms, along with the long gladius and terminal fins, indicates that the morphology of the earliest vampire squids superficially resembled that of modern squids.