Gastropoda and Bivalvia

Gastropoda and Bivalvia

Gastropoda and Bivalvia

Fossil gastropods are known from Cambrian deposits. Since the shell is often very similar in unrelated families, fossil gastropods more than 350 million years old are not usually placed in the classification outlined below but instead are treated separately. Most neogastropod prosobranchs appeared near the end of the Mesozoic (65.5 million years ago), and many groups of land snails are known from Eocene formations (roughly 56 million to 34 million years old).