Of all the molluscs, the gastropods (snails) have made the most ecological adaptations. They can be found in almost all fundamental environments: marine, freshwater, terrestrial. Most gastropods live in the ocean, and have a single, asymmetrically coiled, external shell of calcium carbonate (CaCO3 - usually aragonite). The hard calcareous shell is the most easily fossilized part of the gastropod. The soft parts of a snail (the “slug” portion) include a well developed head having eyes, tentacles, and a mouth, and a well developed, strong, muscular foot used principally for locomotion. The shell is carried upright on the snail’s back, or is partially dragged behind. When threatened by a predator, many snails can retract their soft parts into the shell’s interior for protection.
Many fossil snails in the Paleozoic rock record are often not well preserved, or are preserved as internal molds. The original aragonite of many gastropod shells is not stable on geologic time scales, and often recrystallizes or dissolves completely away. Fossil snail shells in Mesozoic and Cenozoic rocks are usually better preserved. Shown below are some well-preserved, three-dimensional fossil snail shells from the late Cenozoic of America.
Phyllonotus fossil muricid snail shell (5.8 cm tall) - abapertural view (left) & apertural view (right).
Stratigraphy & age: Fort Thompson Formation, Pleistocene
Locality: Largo, Gulf Coast of Florida, USA
Pterorhytis conradi (Dall, 1890) fossil muricid snail shell (3.5 cm tall) - abapertural view (left) & apertural view (right).
Stratigraphy & age: lower Croatan Formation (a.k.a. lower James City Formation), Lower Pleistocene
Locality: Lee Creek Mine at Aurora, eastern North Carolina, USA
Subpterynotus textilis (Gabb, 1873) fossil muricid snail shell (4.6 cm tall) - abapertural view (left) & apertural view (right). Note the predatory boring on the shell in the left photo. Note that the aperture is quite small relative to shell size.
Stratigraphy & age: lower Caloosahatchee Formation, upper Pliocene
Locality: La Belle, southern Florida, USA
Busycon carica (Gmelin, 1791) - a large fossil knobbed whelk shell (Neogastropoda, Muricoidea, Melongenidae), abapertural view (11 cm tall). From the Pleistocene of the Lee Creek Mine at Aurora, eastern North Carolina, USA.