reduction of the shell is associated with a predatory way of feeding. Some taxa lost the coiling of their shell during evolution. According to Dollo's law, it is not possible to regain the coiling of the shell after it is lost. Despite that, there are few genera in the family Calyptraeidae that changed their developmental timing (heterochrony) and gained back (re-evolution) a coiled shell from the previous condition of an uncoiled limpet-like shell. Taphonomic implications In large enough quantities, gastropod shells can have enough of an impact on environmental conditions to affect the ability of organic remains in the local environment to fossilize. For example, in the Dinosaur Park Formation, fossil hadrosaur eggshell is rare. This is because the breakdown of tannins from local coniferous vegetation would have caused the ancient waters to become acidic. Eggshell fragments are present in only two microfossil sites, both of which are predominated by the preserved shells of invertebrate life, including gastropods. It was the slow dissolution of these shells releasing calcium carbonate into the water that raised the water's pH high enough to prevent the eggshell fragments from dissolving before they could be fossilized. Variety of forms References This article incorporates public domain text from references, and CC-BY-2.0 text from reference. Further reading About chirality van Batenburg1 F. H. D. & Gittenberger E. (1996). "Ease of fixation of a change in coiling: computer experiments on chirality in snails". Heredity 76: 278–286. . Wandelt J. & Nagy L. M. (24 August 2004) "Left-Right Asymmetry: More Than One Way to Coil a Shell". Current Biology 14(16): R654–R656. External links Gastropods by J. H. Leal – Information on some gastropods of the tropical Western Atlantic, specifically the Caribbean Sea, with relevance to the fisheries in that region Radiocarbon Dating of Gastropod Shells Nair K. K. & Muthe P. T. (18 November 1961) "Effect of Ribonuclease on Shell Regeneration in Ariophanta sp.". Nature 192: 674–675. . Antonio Ruiz Ruiz, Ángel Cárcaba Pozo, Ana I. Porras Crevillen & José R. Arrébola Burgos Caracoles Terrestres de Andalúcia. Guía y manual de identificación. 303 pp., . (from website) Gastropod anatomy Mollusc shells