Fossils and Geologic Time Topics

Invertebrate Animals (Part 2)


Bryozoans are aquatic animals called “moss animals.”  Bryozoans have existed since the Ordovician.  This specimen is called Archimedes, and is Mississippian in age.

505 to 438 million years ago
505 to 438 million years ago

Archimedes, a bryozoan (Photograph by Parvinder Sethi)


Brachiopods are the single most abundant fossil group in Paleozoic rocks.  Although these creatures resemble clams, they belong to a completely different phylum. 

570 to 245 million years ago

BrachiopodsBrachiopods (Photographs by Parvinder Sethi)

Brachiopods preserved as molds and casts (Photographs by Parvinder Sethi)


Mollusks are extremely abundant in both modern and ancient environments.  They have existed since the Cambrian.  Three major groups of mollusks are shown below: cephalopods (top left), pelecypods (clams) (top right), and gastropods (snails) (bottom).

570 to 505 million years ago

Cephaolopod and Mollusk
Left: Cephalopod; right:pelecypods (Photographs by Parvinder Sethi)

Gastropod (Photograph by Parvinder Sethi)