ORIGIN, EVOLUTION, AND BEHAVIOR OF PALEOZOIC AND MESOZOIC COLEOIDEA (Invited Presentation)

Coleoids (cephalopods with internal conch: endocochleates) play an important role in modern marine ecosystems. As far as fossil cephalopods are concerned, however, much more research focuses on cephalopods with external conchs (ectocochleates: ammonoids, nautiloidsetc.). Coleoid fossils also differ in abundance and mode of preservation from their ectocochleate relatives. Thus, knowledge of endocochleates and ectocochleates also differ, and especially coleoids are rather poorly known.

Recently, some spectacular new discoveries have been made of coleoids preserving soft tissues. These findings revealed interesting details that shed light on their evolution and behavior. For example, the reassessment of the Mississippian (Carboniferous) stem-coleoid Gordoniconus beargulchensis from Montana shows several bauplan characters of the Coleoidea. Notably, this species lacks an ink sac, thus suggesting that internalization of the conch preceded the evolution of the ink sac. Additionally, the fossils show evidence of an arm crown with ten short arms, well sclerotized jaws, a predatory behavior (stomach content with vertebrate remains), improved locomotory abilities, and a well-developed central nervous system, probably combined with a good visual system.

New fossils from Mesozoic conservation deposits of Europe provide evidence for an evolutionary trend towards a further increase in swimming speed and efficient predation on rather large prey. Also, there are indications that some vampyromorphs swam close to the water surface. Additionally, we found Jurassic material showing many organs relevant for locomotion, which we know from living representatives. It appears like there are overarching evolutionary trends among coleoid cephalopods towards increasing swimming speed, improved maneuverability, and enhanced efficiency in predation on large prey including fishes, other cephalopods, and arthropods.