EXCEPTIONALLY PRESERVED CARBONIFEROUS CEPHALOPOD OUTLINES VAMPYROPOD EVOLUTION THROUGH A NEW TIP-DATED BAYESIAN PHYLOGENY

The overwhelming majority of extant cephalopods are coleoids, represented today by Vampyropoda (octopods and Vampyroteuthis) and Decabrachia (squids and cuttlefishes). Despite their modern prominence, fossil coleoids (except for belemnoids) are rare, likely because they have reduced or eliminated their internal phragmocone. Molecular evidence suggests these groups diverged in the late Paleozoic, yet up to now no definitive decabrachians or vampyropods were known from before the Middle Triassic. Here we describe a new Carboniferous (Mississippian) genus and species of vampyropod from the Bear Gulch Lagerstätte. The fossil is preserved with sucker-bearing arms and a simple gladius; it lacks arm hooks, phragmocone, primordial rostrum, and rostrum. A new tip-dated Bayesian phylogeny places this fossil as the earliest diverging vampyropod. Based on this phylogeny, we propose a new outline of vampyropod trait evolution. Vampyropods do not appear to have been derived from a phragmoteuthid-like ancestor, but instead are characterized by the complete loss of mineralized shell tissues soon after diverging from decabrachians and belemnoids.