How Many Horn Corals Are There?

[dudeman]

Hello,

Here is one of my Horn Corals, it is by far the largest one and most complete in my collection. Which brings me to my question...are there different Horn Corals? If so, which one is this? The H.C. was collected here in the Midwest.

[FossilDAWG]

I expect that there are over a thousand genera, and several thousand species of "horn coral" that have been described. To confidently ID a specimen, you need to prepare a series of cross-sections, starting at the tip (the earliest growth stage) and progressing towards the calyx (top) so you can see how the internal structures matured over the life of the animal. For example, in the Ordovician genus Streptelasma there are open spaces between the septa in the juvenile stage, but in the closely related genus Helicelasma the spaces are filled in so the tip is solid. You will also need at least one or two longitudinal sections, to show structures (tabulae, dissepiments, etc). Although the exterior sometimes shows important features, for the most part the external appearance can't give enough information for a firm ID. For example, in the Percha Shale of New Mexico (Late Devonian), there are about a dozen horn coral species in several genera, and externally they all look exactly the same.

Now, most collectors don't have the facilities to make a bunch of thin sections. What you can do is figure out the specific rock formation that your specimens come from, then look for research publications where someone has done the work and gives a list of identified species at least, and even better some descriptions and photos. At least then you may be able to narrow down your identification a lot, or perhaps even get a fairly firm ID if your specimen does correspond to a species with distinctive characters. Again as an example, you can find over a dozen kinds of horn corals at Hungry Hollow in Ontario, and if you know what to look for you can ID all (or almost all) of them without cutting sections. However, if I was given a specimen from there, let's say the common species Heliophyllum halli, but I was not told where the fossil came from or the age, then I would have to compare it to every described species from the entire world to get an ID, and for that I'd need thin sections.

In your case, you have not told us the age of your specimen, the formation it came from, or even a location (there's a lot of rock covering a lot of time in the "Midwest"). Not knowing the age or location, and not having the necessary sections, I have to say no-one will be able to give a realistic ID for your specimens. If you enlighten us as to the age, geological formation, and locality (not GPS coordinates or anything that specific, but a nearby town or known landmark would help), it's possible that someone will be familiar with the fauna and be able to offer suggestions.

Don

[dudeman]

Thank you Don, I was unable to provide that info due to the fact that this is another of my "auction finds". I can tell you the estate auction was in Rockford, IL, but I did not get any other info.