Paléozoïque

Crommium angustatum Grateloup, 1827 fossil snail shell (apical view) from the Oligocene of France. (42 mm across at its widest) 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. Classification: Animalia, Mollusca, Gastropoda, Naticoidea, Ampullinidae Age: Rupelian Stage (Stampian Stage), Lower Oligocene Locality: Gaas, Landes Department, Aquitaine, southwestern France

Crommium angustatum Grateloup, 1827 fossil snail shell (apical view) from the Oligocene of France. (42 mm across at its widest) 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. Classification: Animalia, Mollusca, Gastropoda, Naticoidea, Ampullinidae Age: Rupelian Stage (Stampian Stage), Lower Oligocene Locality: Gaas, Landes Department, Aquitaine, southwestern France

Crommium angustatum Grateloup, 1827 fossil snail shell (abapertural view) from the Oligocene of France. (57 mm tall) 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. Classification: Animalia, Mollusca, Gastropoda, Naticoidea, Ampullinidae Age: Rupelian Stage (Stampian Stage), Lower Oligocene Locality: Gaas, Landes Department, Aquitaine, southwestern France

Quarry called “Ratssteinbruch” at Plauenscher Grund (gorge-like valley of the river Weißeritz nearby/in the city of Dresden, Saxony, Germany), Upper Carboniferous Monzonite (historically identified as Syenite) of the Meißen Massif (Paleozoic basement) unconformably overlain by Upper Cenomanian beds of the Dölzschen Formation, yellowish basal conglomerate and overlying bluish silty clay-marlstone (“plenus-Pläner”) of the Saxo-Bohemian Cretaceous Basin (Mesozoic platform).[1]