Honeycomb Coral ?

[Ameenah]

I found this in a paking lot of all places, it is to big for me to collect without permission and help lol. I think its beautiful I would love to have it cut out and polished, but it looks like it would crumble. I'm thinking it's a honeycomb coral.

[Ameenah]

one more pic

[FossilDAWG]

The term "honeycomb coral" is a reference to the fact that the most efficient way to pack a lot of individual "cells" together without wasting space is to make them hexagonal. Lots of different, unrelated structures have this anatomy: compound eyes of an insect, some corals, and honeycombs. There is no such thing, taxonomically, as "honeyconb coral" it's just collector's jargon, like "devil's toenails".

That being said, the following colonial corals are listed from the Nashville area on Steve Holland's web site. I have added my take on characters that can be used to ID these. Be aware that these characters are not exhaustive, just what might be useful to discriminate these corals from the Ordovician of the Nashville (and adjacent, such as Cincinnatti) area.

Tabulate colonial corals:

# Aulopora Corallites crescent-shaped; often a crust on other surfaces.

# Cyathophylloides Corallites hexagonal; primary septa long, reaching center and twisting together.

# Foerstephyllum Corallites hexagonal; primary septa short, secondary septa about half as long; tabulae flat.

# Lichenaria Corallites hexagonal, generally small (1 to 1.5 mm); septa all of one length; usually small colonies.

# Protaraea Corallites circular, without hexagonal shape, small; septa of one size, so corallite has appearance of an asterisk; colonies always thin, encrusting on surfaces such as other fossils.

# Tetradium Corallites square; four primary septa originating from middle of each side of the corallite. Controversial about whether or not these are actually corals.

Rugosan colonial coral:

Favositella Corallites hexagonal, in some species becoming tubular, free from contact with adjacent corallites; primary septa long, at least 1/2 way to middle of corallite and sometimes almost to center; secondary septa short; tabulae flat or slightly arched.

Note that the division between tabulates and rugosans is somewhat arbitrary at this stage of coral evolution. Some authors propose that certain genera grade into one another as primary septa start short (Foerstephyllum), become longer (Favistella), and eventually meet in the center and twist together (Cyathophyloides). Other authors propose different evolutionary series, in some cases based on microstructure of the corallite walls in exceptionally well preserved specimens, though all agree that Favistella and Cyathophylloides are closely related. It seems to me, personally, that the dividing line between some genera, such as Favistella/Cyathophylloides, is somewhat arbitrary. I also think Cyathophylloides is misplaced on the web site, it should be considered a rugosan, at least if Favistella is going to be listed as a rugosan.

Returning to Ameenah's specimen, the corallites are fairly large (bigger than a couple of mm in diameter), they have flat tabulae (the partitions that divide each individual corallite horizontally), and there are both long (primary) and short (secondary) septa (the spiny looking structures sticking into the corallite from the corallite wall), but even the primary septa are relatively small. Overall it seems pretty definitive to me that this is a Foerstephyllum. Steve Holland's web site lists only one species, Foerstephyllum vacuum, from the Nashville area.

Don

[FossilDAWG]

Here's one of Ameenah's pictures with some parts labeled. Note that in Foerstephyllum the primary and secondary septa are close in length, so the long-short-long-short... arrangement may not be obvious. This is especially true of natural cross-sections where the planes and angles are all over the place, so you may not have a true cross section but rather some parts are at an angle to others, and so intersect shorter or longer paths through the coral. Often you have to look at several individual corallites to see the true arrangement.

Don

[Auspex]

Wow! Thank you Don; this is instructional content !