Halysites Chain Coral Uncovered

Golden Beach grass dune
Oval Beach Saugatuck, Michigan  (Winter 2012)

I was super excited to discover several fossils on Oval Beach in Saugatuck, Michigan, USA that are highly unusual to find in winter. The fossil below was lying under deep layers of sand, but luckily, the mild weather with minimal snowfall allowed winter winds to push sand off the under layers. Also contributing to fossil hunting were the low water levels from a long dry spell during summer 2012, which produced more beach to explore.

Halysite Coral
Halysites Chain Coral Fossil Found on Lake Michigan Beach

These fossil samples are extinct tabulate corals, reef building colony-type corals, Halysites, commonly called, Chain Corals. They are fairly easy to distinguish due to the chain-link raised marks for which they’re named.

Halysites Chain Coral Fossil Found on Lake Michigan Beach

In life, the extinct Halysites corals possessed small tubes where the jelly-like polyps resided. The coral polyps contained stinging cells for protection and also for siphoning plankton and organic matter passing by in the ocean currents. As the Chain Corals grew, they built up walls of tube-like chambers called theca which steadily multiplied while adding more links to the chain. In their heyday, they built large limestone reef structures on the seabed. They thrived especially during the Silurian period as far back as 425 million-years-ago!

Halysites Chain Coral Classification

Kingdom: Animal

Phylum: Cnidaria (means stinging animal)

Class: Anthozoa (means flower animal)

Order:  Tabulata (possess inner horizontal dividing walls from growth patterns)

Family: Halisitidae (means chain coral)

Genus: Halysites  Species: unknown

Halysites Chain Coral Rendering Showing Polyps Extended

Explore more Lake Michigan fossils in another photo-essay I provided, otherwise, keep scrolling!

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What is a favosites?

Favosite Coral
(Charlevoix Stones) Favosites Honeycomb Coral Fossil

A favosites is a type of extinct coral. Favosites coral fossils most identifying feature is the honeycomb-like openings (coralites) revealing where the animal (polyps) lived. The polyp tentacles could tuck inside for safety, typically at night, or stretch out from their calcium-carbonate substrates in order to filter tiny food particles floating by in ocean currents.

Favosite Coral Preserved in Gray Shale
Favosites Honeycomb Coral Fossil Preserved in Gray Shale

The large fossil sample shown first is preserved in sedimentary claystone. It was found in a field in the city limits of Saugatuck, Michigan, part of the Ellsworth-Antrim Geological Formation (Mississippian-Devonian), Allegan County, Southwestern Michigan, USA. This particular type of honeycomb coral fossil is more commonly found in Charlevoix, Michigan, situated in the Traverse Group Geological Formations in the far northeastern region of the state. Consequently, they’re often called, Charlevoix Stones.

The tabulae (horizontal internal layers) place the favosites corals in the order of tabulata with internal chambers that built outward and upwards as the organism grew.

Diagram of Favosites Internal Structure

The walls between corallites were pierced by pores known as mural pores which allowed transfer of nutrients between polyps as illustrated below.

coralmorph2
Favosite Coral Reveals Horizontal "Tabulate" Growth Layers
(Charlevoix Stone) Favosites Honeycomb Coral Fossil Reveals Inner Growth Layers (Found on Oval Beach, Lake Michigan)

Like all coral, favosites corals thrived in warm, shallow, sunlit seas. They were a colony type coral forming colorful quilt-work reefs and fed by filtering microscopic plankton with their stinging tentacles. They were most prevalent during the Silurian and Devonian time slots, but date as far back as the Ordovician and forward to the Permian between 251-488 mya. That’s over 200 million years of living on earth . . . amazing!  

Favosites Honeycomb Coral Fossil

Favosites Classification

Common Name: Honeycomb Coral        Scientific Name: Favosites 

Kingdom: Animal

Phylum: Cnidaria (means to sting)

Class: Anthozoa (means flower animal)

Order:  Tabulata (possess inner horizontal dividing walls)

Family: Favositidae (honeycomb pattern on exoskeleton)

Genus: Favosites Species: Alpenensis (Charlevoix Stone)

Cora Honeycomb-studio textre
Rendering Drawing of Extinct Favosites Honeycomb Coral Showing Polyps Drawn-out

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