Evolutionary history of naticid shell-drilling predation

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1. Based on anatomical research of a living fossil snail, Globularia fluctuata (Sowerby), this snail has a primitive nervous system and shares many features common to freshwater ampullariid snails. Also, G. fluctuata is grazer rather than predator. This discovery suggests that 1) naticids first appeared in mid-Cretaceous, 2) many Cretaceous and most of Jurassic "naticids" are not naticid, and 3) the Jurassic and Cretaceous did not feed on molluscs by shell drilling. Therefore, it appears that the fossil record of naticids and their predation traces are in harmony with each other. Our discovery supports a hypothesis that naticid predation appeared in mid-Cretaceous.2. We have shown that there are some boreholes similar to the incomplete drillholes by naticids. One example is the limpet home scars in the Cretaceous ammonites from Japan and Sakhaliin. Limpet home scars are produced by territorial and/or homing species by, means of Chemical dissolution, assisted by radular action. However, limpet home scars differ from the incomplete naticid drillholes in shape and size. Rediscovery of a Placenticeras meeki from South Dakota with many home scars and patellogastropod Limpets strongly suggests that the so-called mosasaur bite-marks are also home scars of patellogastropod limpets.3. We have shown that shell-elongation of marine snails is an example of anti-predatory adaptation agains naticids. Although this study is in progress, it is evident that elongate shell has more naticid drillholes than round ones.