COMMON FOSSILS of INDIANA Fossils are the preserved remains of creatures from long ago. Most Indiana fossils are from the Paleozoic Era, 542 million to 250 million years ago.During that time, Indiana was covered periodically by shallow seas. Thus, the majority of Indiana fossils are marine fossils. Brachiopods are among the most common fossils in Indiana rocks.They resemble clams, but are a distinct type of marine animal. Bryozoans live together in colonies and form branching stemlike, lacy, or encrusting forms.OMMON FOSSILS of INDIANA Fossils are the preserved remains of creatures from long ago. Most Indiana fossils are from the Paleozoic Era, 542 million to 250 million years ago.