Well, here’s a weird one for you! This comes to us from Dale Gnidovec at the Orton Geological Museum at OSU. When he told me about this specimen, I thought “No, that can’t be real” but here it is! It’s not from Ohio, but is just too freaky not to use in this series! More than likely you have never seen one of these, but what does it look most like to you that is from Ohio!? The object is fairly small, only about an inch across. Thanks to Kellie Locke-Rogers for the photos.

Answer:

It is indeed a square horn coral, Goniophyllum pyramidale. In life this animal had four triangular flaps, known as opercular valves, which would have covered the opening. This specimen is from the Silurian Period, approximately 430 million years old, and was collected in Gotland, Sweden.

In Ohio we’re used to seeing the common horn corals, which were found throughout most of the Paleozoic Era. The photo is a of solitary rugose coral (“horn coral”), Zaphrentis, from Indiana but is also found in Ohio. You’ll notice that the ridges inside the coral, known as septa, are similar between the European square coral and our commom horn coral; a clue that the unusually shaped specimen is probably a coral!

Thanks to Dale Gnidovec, Curator of the Orton Geological Museum, for the idea and for providing the information about the specimen.