The USGS offers a more detailed list of invertebrate fossils (with scientific names only) here.Other major index fossils are small or microscopic, part of the floating plankton in the world ocean. They can be found even in small bits of rock, such as wellbore cuttings.The rocks of the ocean floor are geologically young, as they are constantly subducted and recycled into the Earth's mantle.
Because they were mobile animals, they tended to inhabit large, even global areas.
They were also hard-shelled invertebrates, so they fossilized easily.
These fossils are large enough to study without a microscope.
Other index fossils of this type include ammonites, crinoids, rugose corals, brachiopods, bryozoans and mollusks.
Jessica's other ancestry includes English, German, Swiss-German, Scottish, and distant Welsh, Swedish, and ...