Most Common Mollusk Fossils

Sea Shells

• The first mollusk fossils appear in Cambrian rocks. There are several hundred species of mollusk shells found in rocks from the Cambrian era. Creatures such as snails live inside shells. When they die or are eaten, the shell remains. The shells look like cylindrical shells or like conch shells. The fossil record is full of these remains in areas where there were prehistoric seas, like the American Southwest and the state of Kentucky.

Squids and Octopi

• The largest animals without backbones are squids and octopi. Some scientists think the largest of these creatures have not even been seen. The giant squid and the colossal squid are the largest known of these species. Unlike the living sea creatures of squids and octopi, the common fossils of these creatures have developed shells, which were fossilized. Their scientific name is Cephalopoda. They date back to the mid-Cambrian era, not back as far as snails, slugs and other early Cambrian fossils.

Worms

• There is continued scientific debate about very early mollusks and worms. There are small organisms with evolutionary ties to mollusks that can be found readily in the fossil record. In the rocks they appear as small, thin lines, like pieces of thread. Some were mollusks, as the sections of their bodies can be identified, but there is doubt about others. Nonetheless, they are very common fossils.

Clams

• One of the most common evidence of mollusks found in the fossil record are what are commonly known as seashells. The fossils of these fan-like shells can be easily found in the fossil record of ancient oceans. The shells were once clams and resemble contemporary clam shells. The structure of the clam shell has not evolved much since the Cambrian era. Clam shell fossils date back to the early Cambrian period. Although there is not official counting of their numbers, clam shell fossils are considered common.