Bryozoa of the Cincinnatian
By Jack Kallmeyer

Constellaria florida


What Bryozoa are: Bryozoa are colonial animals that secreted a hard limy skeleton much like corals. The colony consists of thousands of individual animals each living within their own tube (aperture). The living tubes are the size that a sewing needle might make. Sometimes the outer surface is covered with distinctive bumps or ridges (monticules). Colony shapes vary from delicate open mesh fronds to branching forms, massive mounds, and heavy dense fronds. Sometimes one colony will show multiple forms.

Bryozoan fossils found in the Cincinnatian are marine animals. The animal itself is biologically advanced and has both a mouth and anus. Bryozoa are filter-feeding animals that capture microscopic food floating past them in the water. The food gathering mechanism is a feathery looking device called a lophophore.

What Bryozoa are not: Bryozoa are not corals. While colony shapes sometimes resemble the branching forms that we are familiar with for modern corals, there are some easily observable differences. The tube that a coral animal lives in within the colony is much larger than those needle sized tubes of the bryozoa. The dwelling tubes of corals are also filled with radial dividing ridges called septa - the bryozoan tube has no filling and appears as a simple hole. The biology of the coral animal is simpler in that it does not have a pass through digestive system - food is taken into the mouth and waste products later expelled from the mouth. The food gathering mechanisms of corals are tentacles.

Bryozoa are not plants. Some of the preserved stony skeletons of Cincinnatian bryozoa are branching colonies resembling twigs of a tree. Bryozoa are animals, not plants. At the time in earth history when the Cincinnatian sediments were laid down, between 451,000,000 and 443,000,000 years ago, no advanced vascular plants existed on the earth.

Identifying Cincinnatian Bryozoa: The good news about Cincinnatian bryozoa is that they are by far the most abundant fossils found in the area. The bad news is that positive identification to species level is not possible by external appearance for most of them. Paleontologists must cut, grind, and polish specimens to examine the microscopic internal structure to identify these fossils.

The photographs on this page illustrate the few bryozoan types that can reasonably be identified by collectors with some certainty.

The Specimens:

Escharopora falciformis

Escharopora falciformis: A flat blade-like frond with diamond shaped apertures. This specimen was found in the Fairview Formation of the Maysvillian Stage.


Escharopora hilli

Escharopora hilli: A flat blade-like frond with ridges running completely around the frond. This specimen was found in the Fairview Formation of the Maysvillian Stage.


Graptodictya perelegans

Graptodictya perelegans: A flat frond with large (2 to 4 mm) openings running through the frond. The apertures cover both sides of the entire specimen (compare to the Fenestrate Bryozoa below). This specimen was found in the Fairview Formation of the Maysvillian Stage.


Constellaria florida


Constellaria florida: A twig-like to frond-like colony with monticules shaped like stars. This species is found in the Fairview Formation of the Maysvillian Stage.


Constellaria polystomella

Constellaria polystomella: A twig-like to frond-like colony with monticules shaped like stars. This species is found in all Formations of the Richmondian Stage.


Ropalonaria venosa

Ropalonaria venosa: This bryozoan does not build its own stony skeleton. Instead, it etches its way into the shells of other animals. This species can be recognized as a network of slits (the apertures) linked by finer lines. This species was found in the Richmondian Stage and has etched its way into the shell of a brachiopod.


Rhombotrypa quadrata

Rhombotrypa quadrata: Close examination of the apertures of this species reveals four-sided "square" openings. This species was found in the Richmondian Stage.


Spatiopora sp

Spatiopora sp.: A number of species exist in this genus. Many of them are found growing on the shells of cephalopods. Many of these species have elongated monticules whose long axis aligns with the length of the cephalopod. This species was found in the Richmondian Stage.


Cyclostomate Bryozoa

Cyclostomate Bryozoa: Many species are known from this group and expert help is needed for identification. These animals all form web-like patterns on the surface of other animals' shells. The web-like pattern is made up of a series of teardrop shaped mounds with an aperture in each mound. This species was found in the Richmondian Stage.


Fenestrate Bryozoa

Fenestrate Bryozoa: These are all very small delicate frond-like bryozoa with an open mesh appearance. The apertures are spaced along only one side of the frond - The apertures are on the back side and not visible in this photograph.


Reconstructed Colony

Reconstructed Colony: This is a reconstructed colony of unknown species identification. It is typical of the twig shaped branching colonies found throughout the Cincinnatian.

Click HERE for pictures of Ron Fine's Excellently Reconstructed Bryozoans  

Click HERE for photos of Bryozoans found on our field trips

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