Jet propulsion of Nautilus: a surviving example of early Paleozoic cephalopod locomotor design

Abstract

Like its coleoid relatives, Nautilus swims by jet propulsion. However, in the structure and functioning of its motor, Nautilus differs markedly from its contemporaries. Compared with that of squids, Nautilus locomotion is based on small propellant volume, low mantle cavity pressure, low propellant velocity, and small propulsive muscle mass. Propulsive performance of Nautilus is consequently unspectacular, with as little as one-eighth the thrust and one-tenth the burst speed observed in squids of equivalent size. Nautilus survives as a result of its slow-moving, vertically mobile, foraging life-style limited to habitats where competition with fast-moving, agile swimmers is minimal. Fossil cephalopods faced similar design constraints, which may have contributed to their decline, but nonbiologic factors such as sea level fluctuations may also have been important in directing the course of cephalopod evolution.