Cnidarian Fossils

From Ohio History Central

Cnidarians are the simplest animals having many specialized cells, a mouth, and a true digestive cavity. Other than corals, most cnidarians have no hard body parts, and therefore generally do not fossilize.


Habitat:Acquatic, mostly marine; attached to the bottom or floating.
Modern Forms:Hydra, jellyfish, sea anemones, and corals. About 10,000 living species.
Geologic Span:Precambrian to present.
In Ohio:Found in rocks from Ordovician to Permian age.


Corals form one group within the Cnidarians. They have hard skeletal structures and are relatively common as fossils.

Some coral animals live together in colonies. The individuals are permanently fastened together. Other corals live alone as individuals. These are known as "solitary" corals.

Living corals today are responsible for building the great coral reefs in tropical oceans.


These honeycomb coral animals lived together in colonies. They are found in Silurian and Devonian rocks (about 438 – 360 million years ago). Several kinds of Favosites occur in Ohio.

Polished Specimen of Favosites

When cut and polished, some fossils make attractive objects.


These fossil corals occur in rocks of Devonian age. When living, the tubular corals formed small, shrub-like colonies.


These big colonial corals usually have large hexagonal shaped tubes. They occur in rocks of Devonian age.

Polished Specimen of Hexagonaria

A person has cut and polished this specimen.


These colonial corals are made of long, upright tubes that are connected. In Ohio they occur in Ordovician and Silurian rocks.


These horn-like corals were common in Ohio . They occur in rocks of Ordovician through Devonian age.


  • Rhodes, Frank H.T. Fossils: A Guide to Prehistoric Life; Golden Press, New York; 1962.
  • Skinner, Brian J. & Stephen C. Porter The Blue Planet: An Introduction to Earth System Science; Wiley, New York; 1995.

See Also