Hexagonaria
genus of cnidarians (fossil)
Hexagonaria is a genus of colonial rugose coral. Fossils are found in rock formations dating to the Devonian period, about 350 million years ago. Specimens of Hexagonaria can be found in most of the rock formations of the Traverse Group in Michigan. Fossils of this genus form Petoskey stones, the state stone of Michigan. They can be seen and found in most Midwestern U.S. states.
Hexagonaria is a common constituent of the coral reefs exposed in Devonian Fossil Gorge below the Coralville Lake spillway and in many exposures of the Coralville Formation in the vicinity of Coralville, Iowa.
Species Identification
Based on Erwin C. Stumm's Corals of the Traverse Group of Michigan Part 13, Hexagonaria, published in 1970. Notably, other species of Hexagonaria occur in rocks outside the Michigan Basin; those other species are not covered by the chart below and may overlap with the species below in size and numbers of septa. Other features diagnose the differences between species; the metrics below merely represent handy features for diagnosis in the Michigan Basin, not comprehensive diagnoses.
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References
"Hexagonaria".
Begin with the source’s own compact description: “Hexagonaria” is genus of cnidarians (fossil). The dossier treats that line as a proposition to test through Hexagonaria, genus and cnidarians, not as a finished interpretation.
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The phrase “genus of cnidarians (fossil)” supplies a clear boundary for inquiry. It also exposes the unanswered questions: who defined that boundary, when it became stable and which sources sit outside it.
The date and method of observation matter as much as the stated conclusion, especially where classification or consensus has changed. The source revision retrieved here is dated Mar 25, 2026. The linked authority identifier is Q16983143. None of the 0 selected statements returned an explicit reference. The first chronological checks are 1970.
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This entry incorporates text from “Hexagonaria” on English Wikipedia. Contributors are listed in the page history. Text is available under the Creative Commons Attribution-ShareAlike 4.0 License. Selected authority identifiers and statements are retrieved from Wikidata under CC0; their references and qualifiers remain part of the verification path.