THE FOSSIL RECORD OF FORCE AND POWER: GASTROPOD SHELLS AS OFFENSIVE WEAPONS

Rapid subjugation of prey is often advantageous to a predator, because it reduces exposure of the predator to enemies and enables the predator to gain access to food more quickly. During the subjugation phase of a predatory attack, speed is achieved either through the application of venom (not inferable from shell traits) or by the use of force to break, enter, or disable prey. Application of force is reflected in preservable shell traits, including a labral tooth (a projection at the edge of the outer lip), a medially convex outer lip (associated with chipping or wedging bivalve prey), a large aperture (associated with a large, powerful, and flexible foot», and, more speculatively, a strongly crenulated outer lip. Predatory gastropods without these specializations, or with their opposites (e.g. a small aperture), either drill their prey through the shell wall or feed on soft-bodied prey lacking skeletal impediments. Studies of fossils indicate that most of the force-related specializations were present by late Cretaceous (Campanian) time, but in general, Neogene gastropods show higher incidences and greater degrees of specialization of force-related shell features than their Paleogene or Cretaceous counterparts. Moreover, Neogene predatory gastropods with these traits are markedly larger than earlier predatory gastropods. I suggest that these patterns indicate an increase in predatory power (expressed as force per unit time during the subjugation phase) among those gastropods that use force in subduing victims. This trend is part of a larger trend driven by competition among top consumers.