File:Gastropod fossils fluorescing (Bridger Formation, Eocene; Uinta County, Wyoming, USA) 2 (32243849762).jpg

Gastropod fossils from the Eocene of Wyoming fluorescing under ultraviolet light. (public display, Utah Field House of Natural History, Vernal, Utah, USA)

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.

Why do some rocks, minerals, and fossils fluoresce under ultraviolet black light (UV)? When atoms are bombarded by short-wavelength UV radiation, long-wavelength UV radiation, or x-rays, electron excitation occurs, but the electrons do not remain in an energetically excited state. They quickly give off energy and resume their normal energy levels. If the electron energy release is in the visible spectrum of light, a mineral glows, or fluoresces.

Classification: Animalia, Mollusca, Gastropoda

Stratigraphy: Bridger Formation, Eocene