Other
Black Hills Institute of Geological Research, Inc.: Ammonoids
Ammonoids, more commonly referred to as Ammonites, are the extinct ancestors of today's octopus, squid and nautilus. This page provides excellent information about these creatures, as well as diagrams and pictures.
Other
University of Wisconsin: Invertebrate Fossils of Wisconsin
A great collection of invertebrate fossil pictures, accompanied by a description of the fossil and where it was found.
Indiana University
Indiana Univ. Bloomington:geo Notes: Conodonts: Microfossils of Distinction [Pdf]
Presents some facts about conodonts, extinct eel-like animals whose fossils have been found in Indiana's marine sedimentary rocks. Their important role in geologic research is also discussed.